STONE WORK



STONE WORK

5.1. Stone

5.1.1. Requirements of a good structural stone - Structural stones should primarily be (a) strong against crushing, (b) durable, (resistance to weather), (c) good in appearance (colour), (d) susceptible of being quarried in large sizes, and (e) fire resisting.

The strength of a stone depends upon its density and weight.

5.1.2.1. Classification of rocks – Rocks are classified according to:-

(1)Geological formation and (2) Chemical composition.

1. Geological formation - The three classifications are:-

a) Igneous rocks - These are the result of consolidation of molten material or at below the surface of earth, e.g., Granite, Basalt and Trap.

b) Aqueous or sedimentary rocks - These are precipitated by the deposition of sand, gravel, clay, etc., generally by precipitation in water, subsequently cemented together by silica, lime, potash, etc., sided by the pressure of superincumbent layers of material and water, e.g., sandstones, limestone’s, etc.

c) Metamorphic rocks - These are rocks originally formed in either of the two processes mentioned above, but subsequently changed or metamorphosed in colour, structure and texture, having been subjected to either intense heat or pressure exerted by the movements in and below earth’s crust or both, e.g., Slates, schist, marble, etc.

5.1.2.2. Chemical composition – This classification is made on the basis of the chief constituent material in the rock.

(a) Siliceous rocks - Where silica in the form of sand, quartz, or flint, predominates, e.g., granite, trap, sand stone.

(b) Calcareous rocks - Where calcium carbonate lime is the main constituent,e.g. limestone, marble, etc.

(c) Argillaceous rocks-In this argile (clay) forms the base, e.g., Slate, Laterite, etc.

5.1.3. Quality of good stone and comparative strength - A stone of igneous origin is stronger than one of sedimentary formation.  Stones with silicates as binding material will weather better than those with calcareous binding material.  Generally, crystalline stones are hard and compact and are superior to non-crystalline stones.  Finer the crystalline structure, stronger and more durable is the stone.  An examination of old structure, where it has been used will indicate durability.  If tool marks are visible, the edges or corners are still sharp and true and the surface hard showing no signs of deterioration, the stone may be regarded as satisfactory.  A fresh fracture of good stone, suitable for structural work should be bright, clean and sharp, free from loose grains, and should not have an earthy smell.

For dressing, stone should be comparatively soft, yet durable, compact grained and homogeneous in texture, rather than crystalline, free from veins and planes of cleavage.

The specific gravity of a good stone should not be less than 2.7.

5.1.4. Stones used in building construction - The principal stones used in building construction are granites, gneiss, trap or basalt, quartzites, laterites, schists, lime stones, sand stones, pot stones and slates.

a) Granites – A. typical granite contains large proportion of feldspar than quartz, mixed with little mica, either the Muscovite or the Biotite variety.

(1) Syenite is a variety of granite, composed of orthoclase feldspar and hornblende.

(2) Diorite is another variety of granite containing plagioclase (feldspar with inclined   planes or cleavage) and hornblende or some other Ferro magnesium silicate often associated with free quartz.  It usually occurs as introduced in masses in the form of dykes.

(3) Mica is a source of weakness in granite.  If the feldspar is of the orthoclase variety, the granite is not very strong.

 (a). The best form of granite is that which contains a large production of quartz plagioclase feldspar and very little mica.  If it is fine grained, it can be easily worked and polished and used for ornamental works also.

(b) Gneiss - A metamorphic rock.  Gneisses are grouped according to the nature of the dark mineral present in the sample or according to the type of igneous rock to which they are most related.  Normal granite is a massive rock without foliation.  Normal granite is a massive rock without foliation; when it talks foliated structure subsequent to its crystallisation it is termed gneiss.

(c) Trap or Basalt - Both are igneous rocks.  Trap contains feldspar and hornblende while Basalt, which contains feldspar, augite and iron.  Both are fine grained.  They are very compact, hard and durable stones.  They are rather hard to work and obtainable in small sizes and not obtainable in large blocks.

 (d) Quartzites - Derived from the metamorphosis of sandstones or conglomerates.  It is very hard to work and breaks up into irregular sizes and large blocks are not available.

(e) Laterites - are clay stones with a vesicular texture, the vesicular being impregnated with iron in cellular structure.  It is a soft rock suitable for light buildings.  It contains moisture (quarry sap) when freshly quarried and is thus very easy to dress at that time.  After exposure for a month or two, it becomes harder.  It is very easy to work but care is required in selection of stones.

(f) Schists - Metamorphic rock belonging to group of foliated rocks.  Finer in texture than gneiss. Derived either from igneous or sedimentary rocks.  Varieties are named according to the abundance of ferro-magnesium mineral.  Chief among the members of this family that are found in this State are hornblende schists, chlorite schists, calcite schists, and mica schists.  The rocks are generally dark in colour.

(g) Lime stones - are those in which calcium carbonate forms the base. Sand Stones – are those in which silica constitutes the base.

(h) Slates - are fine grained compact argillaceous rocks with planes of cleavage, independent of the original beds, often crossing them at a great angle.

(j) Pot stones - Impure form of Talc, composition being chiefly silicate of magnesia and is not useful for structural work.  It is very easy to work.  The best variety is red variety.  Mottled and streamed colours pervading it should not be very unevenly distributed.  It should not be used in places where it is subjected to any great pressure and liable to be soaked with water.

5.1.5. Ornamental building stones - The following varieties can take fine polish and are mainly used as ornamental building stones

(a)Grey rocks - Which include the medium to fine grained and coarse grained granite gneisses and granites. These are useful for decorative purposes and are available from Sarakki quarries and Malsandra quarries near Bangalore.

(b)  Porphyritic granite - coarse grained granite having grayish colour with slightly pinkish tinge.  The polished surface of the rock gives a mottled appearance with large plates of dull white plagioclase and pale pink orthoclase occurring in a grayish ground mass having quartz and biotite. These are available from certain quarries in Chitradurga District.

(c) Pink rocks - This group has been divided into (a) non-Porphyritic and (b) coarse porphyritic types, the former occurring near Ramnagaram, Magadi and Chamundi Hills, and the latter near EIlikal and Sivaganga.

(d) Green rocks - These rocks are available in Chikmagalur Taluk.(

e)Black rocks - Occurs as an outcrop about two miles east of Mysore on the Mysore-Mahadevapur Road.  It is compact and soft and takes good and lasting polish.

(f) Black trap (Turuvekere Stone) - Occurs in the form of a huge dyke to the east of Kadehalli, a village 6 miles south of Turuvekere.  The rock is soft compact and black when fresh.  It has a grayish appearance on weathered surface; Quarries near Banasandra also yield good samples.

(g)  Felsites and porphyry - Occurring in the form of dykes of quite a great range of texture and colour. Outcrop conspicuously in the Srirangapatnam and Mandya Taluks; when cut and polished they form ornamental building stones.

(h)  Marble - It is a compact, crystalline and the strongest and most durable variety of limestone formed by the metamorphic action.  It is obtainable in a variety of colours, white, grey, blue, green, yellow.  It can be easily sawn and carved; it takes high polish.

 (i) Artificial Stones - Processes have been invented for the manufacture of artificial stones for use in localities where natural stones cannot be had.  Some of the processes produce of high quality.  Comparative cost of producing artificial stones for use in any locality should determine its adoption.  The facility with which it can be moulded to most intricate forms, however, makes it more economical than carvings in natural stone.

Artificial stones are practically forms of good setting mortar or of concrete.

(1)  Artificial stone is made by mixing dry sand with silicate of soda (dissolved flint) and a small proportion of powdered stone or chalk.  These are thoroughly mixed together in a pug or mortar mill, and forced by hand into moulds. A cold solution of chloride of calcium is poured over the blocks turned out, which are then immersed in a boiling solution of the same, sometimes under pressure, so as to entirely fill the pores of the material with the solution.  After this the blocks are found to be as hard as most building stones.  The excess of sodium chloride is washed off to prevent efflorescence. This stone has been used for a variety of purposes.

(2)  Victoria stone  -  A mixture of four parts of crushed granite with one of Portland cement is allowed to set for three days or more into a hard block moulded to the required shape.  It is then immersed in silicate of soda for some seven or eight weeks.  This stone also has been used for various purposes.

(3) Silicated stone - Is made in the same way as Victoria stone, and used for paving slabs and drain pipes.

(4) Artificial paving slabs and paving stones - of many kinds are used nowadays.  They are often composed of Portland cement concrete very carefully made.  Silicates are sometimes added to give hardness to the mass.

5.1.6. Quarrying stones - The open part of natural rock, from which useful material is obtained by loosening or blasting or both is called a quarry, and the process, quarrying.  There is not much difference between quarrying and mining, except that a quarry is open at surface, whereas mining is done underground.

The quarrying should be done in quarries approved by the Executive engineer and the methods of quarrying should be as per standard procedures.

The rock loosened shall be cut into the required sizes by weight, chisels or butt hammers as per requisitions.  Quarry chips shall be removed and stacked separately.

The quarrying for face and cut stones shall be made in selected quarries.

Stones required for dimensioned work to be quarried true and square and as near the dimensions given as possible.

5.1.7. Methods of quarrying - The methods commonly adopted for quarrying stones are as follows:-

1) Quarrying stones

a) by wedging and splitting and

b) by chiseling.

2) Quarrying stones by burning.

3) Quarrying stones by blasting.

 (1).Quarrying stones.

(a). By wedging and splitting - Wooden or steel wedges are used along lines of cleavage.  When these wedges are driven and hammered, the rock yields along the lines of cleavage and blocks are then chiseled and taken out.

(b) By Chiseling - This is done by boring small holes at suitable intervals, one inch to three inches deep with the chisel, inserting steel wedges into the holes and gradually hammering the wedges.  A crack then appears along the line of the holes, and the boulder is split.  The same process is repeated until the stones are cut to the required smaller sizes.

When the stone is a huge boulder, a whole varying from three feet to six feet in depth is drilled and blasted with gun powder only.  It is further split into sizes with chisels and wedges.

(3). Quarrying stones by burning and splitting - Lines of cleavage are created by burning rock and cooling it and then wedging along such cleavages.  But such stones are naturally weaker.  The thickness of stone got depends upon the area exposed to heat and intensity of heat applied.  This causes the layer to expand and separate from the lower mass.  This is usually attended with a dull bursting sound.  This method could be adopted in the case of taking out slabs of fairly large size from 50 mm.

(4). Quarrying of Stones by blasting – See Section 2.

5.1.8 - Dressing of stones -  After quarrying, stones are to be wrought or dressed to varying degrees, depending on the kind of work on which they are used.  It is better to do as much dressing as is possible at the quarry.

Dressing of stone is done in three operations.

(1) While sorting out stone for different useful purposes such as bases, caps of pillars. Arch stones, corner stones, coping, etc., a stone are roughly hewn with a quarry hammer of about 3kgs weight to reduce its weight to minimum by knocking out unwanted materials.

(2) It is then hauled up and it is given the rough shape (by a mason’s hammer of weight 1 to 1.5 Kgs), of a rectangular block for which it was originally sorted out.

(3) Final dressing is done on the site of works by tools such as pitching tool, point chisel, plane or toothed chisels.

5.1.8.1. Blocks of stone, which are to be put into the masonry, should be dressed with horizontal beds and vertical faces, or very nearly so to have proper joints for the specified distance from the face.  If not carefully superintended, masons will chip off the edges of stone with a hammer leaving full joint for perhaps half an inch from the face.

5.1.8.2. Chisel drafted margin - The dressing done with a drafting chisel in narrow strips of width generally 2 to 5 cm. Chisel drafted margin shall be punch dressed.

5.1.8.3. Hammer dressed surface - A hammer dressed stone shall have no sharp and irregular corners and shall have a comparatively even surface so as to fit well in masonry.  Hammer dressed stone is also known as hammer faced, quarry faced and rustic faced.  The bushing from the general wall face shall not be more than 40 mm on exposed face and 10 mm on faces to be plastered (Fig.1).

5.1.8.4. Rock faced surface - A rock faced stone shall have a minimum of 25 mm wide chisel drafted margin at the four edges, all the edges being in the same plane (Fig.2).

5.1.8.5. Rough tooled surface - A rough tooled surface shall have a series of bands, made by means of a plane chisel 4 to 5 cm wide, more or less parallel to tool marks all over the surface.  These marks may be either horizontal, vertical or at an angle of 450 as directed (Fig.3). The edges and corners shall be square and true.   The depth or gap between the surface and straight edge, held against the surface shall not be more than 3 mm (Rough tooled stones are used where fairly regular plane faces are required for masonry work).

5.1.8.6. Punched dressed surface - A rough surface is further dressed by means of punch chisel to show series of parallel ridges.  The depth of gap between the surface and a straight edge held against the surface shall not exceed 3 mm (Fig.4).  Punched dressed stones are used where even surfaces are required.

5.1.8.7. Close picked surface - A punched stone is further dressed by means of point chisel so as to obtain a finer surface, ridges or chisel marks left over being very tiny.  The depth of gap between the surface and a straight edge kept over the surface shall not exceed 1.5 mm (Fig.5).

5.1.8.8. Fine tooled surface - Close picked surface is further dressed so that all the projections are removed and fairly smooth surface is obtained.  The surfaces shall have 3 to 4 lines per centimeters width depending on the degree of hardness of stone and degree of fineness required (Fig.1 to 6).  This type of dressing is commonly adopted for ashlar work.

5.1.8.9. Polished surface - Surfaces having a high gloss finish.  Polishing of stones shall be done by rubbing them with suitable abrasive, wetting the surface where necessary with water.  Alternatively polishing of stones shall be done by holding them firmly on the top of revolving table to which some abrasive material like sand or carborundum is fed.  The final polishing shall be performed by rubber or felt, using oxide of lime (called by trade name as putty powder) as a polishing medium.

5.1.8.10. Moulded - Cut to profile of a moulding with punched dressed surfaces, unless otherwise specified.

5.1.9. Weathering of stones - The effect of weather on building stones.

5.1.9.1. “Weathering” is understood to mean the gradual wear or decay brought about by any cause and a ‘perfect ‘ material would resist these decaying agencies and remain always in original state.  There is, of course, no ‘perfect’ material, but many forms of stones get very close to the state of perfection as witness the ancient monuments that have withstood the ravages of times for thousands of years.

5.1.9.2. Chief agents of destruction or cause of failure in building stone. 

(1) Frost or severe and sudden changes in temperature.- Frost causes the water that has penetrated into the pores of stones or between the laminations to expand on freezing.  The expansion has a loosening effect on the particles.  Sudden changes in temperature have a somewhat similar effect on the particles, of which the stone is composed.

(2) Failure of the structure of the stone - This may happen in untried qualities particularly, sandstone, where grains of practically indestructible silica may be held together by a weak cementing material.

(3) Drawing rain - Rain (and atmospheric moisture generally) is charged with sulphurous acids which act on the carbonate of lime in a limestone setting up chemical action which gradually eats the stone away. The action is very gradual of course but care should be taken to choose a good limestone for use in Industrial towns where decay from this cause may be most expected.

(4).  Dust and sand laden winds- This may be only a minor cause excepting for a few isolated stones that are in such a position as to be always affected by dust.  Sand - in really sandy districts can however leave a very marked effect on work, a very famous example being the sphinx in Egypt.

(5) Vegetation - Clinging mosses, lichens, and similar parasitic vegetations look very beautiful on stone work but they have a disintegrating effect if only through the retention of moisture.  There are however other causes which may be very serious. They are not included under “chief causes” as they are due (a) to misuse of the material, and (b) bad design.  Under (a) comes the grave fault of using sedimentary rock, the wrong way of the bed.  The use of iron clamps, rods or dowels, etc., is also liable to cause failure due to the expansion of metal during oxidisation.

5.1.10. Preservation and restoration of stones - There is in fact no distinct dividing line between preservation and restoration.  The ultimate finish required also plays a large part, as for example, a domestic residence must be treated quite differently from an ancient monument.

(1). Preservation - To apply a preservative to a stone with the object of making it permanently weather – resisting whilst at the same time retaining its natural colour and appearance is practically impossible.  Certain measures can however be taken to increase the life of a stone and arrest decay.

There is no such thing as a single solution, which can be universally adopted for preserving any kind of stone.  It stands to reason that stones of different chemical composition and physical properties must receive separate and distinct treatment.  However, there are a number of preservatives in the market.

(a). Chemical and patent preservatives - There are now many of these in the market, most of which are efficient for a few years if applied carefully.  Silicate of soda is the basis of many of them.  The object aimed at in these liquids is to produce a substance that will combine with the carbonate of lime and make an impervious surface.  Best results are obtained if the solution is applied when the work is new.  The silicate of soda in solution when applied penetrates the pores in the surface and reacts chemically with the free lime.  Insoluble calcium silicate and silica are formed and as a result the pores in the surface layer are “sealed”.

A good preventive, which is better than a preservative is the frequent, washing down of the work with, cleans water.  This removes the acids before they act on the stone.  But this process should not be adopted in frost weather. Both organic and inorganic preservatives are subject to decay and must be renewed from year to year. Before applying any preservative the faces of the work should be well cleaned and any loose particles removed by forced water or brushing and the liquid applied when the stone is dry. Paint is a good preservative but it has a limited life and also the great disadvantage of destroying the appearance of the material.  Boiled linseed oil is also very good but destroys the colour of the stone.

(b). Paraffin wax - Effective to a degree if it can be applied hot and driven well into the intestacies of the stone.

Coal tar and bitumen are very good preservatives but their colour is objectionable and besides they absorb the sun’s heat.

(2) Restoration - Failure in stones can be prevented if sufficient care is taken in the original choice and use of the stone itself.  Faults as fractures caused by the oxidization of iron, cannot be successfully repaired by an application of a preservative.  Affected stone should be cut out and replaced. When considering the restoration of stone work, the method or methods used depend entirely on the class of work and the extent to which it has decayed and worn. If the decay is not serious, all dust and dirt can be cleaned off with wire brushes or water and the surface then coated with a stone preserving liquid when the work dries.  Another method is to cut out the defective part to

A depth of not less than 20 mm and render them over with a mixture of cement and stone dust.  2 to 2 ½ of stone dust and 1 of white cement usually make a suitable mix for limestone.  The bottom of the sinking should be roughened and several undercut holes drilled in it to give a key for the cement. For large restoration jobs, where it is desirable to restore the work to its original condition, by far the best method is to cut out any defective stones and replace them with new ones of the same material.

The cutting one should be to a depth of 75 to 100 mm or more if the stone in question has a large projection and the new stones should be dowelled to the one next to it or clamped back to the wall itself.  The joints can then be painted up and grouted solid.  This grouting is essential and it is important that it should be solid.  To ensure this, two holes should be left at the top of the block either by leaving out the pointing or better by making holes for the purpose.  One hole is to pour the grout into and the other to let the air out and prevent an air lock (which would make the joint appear to be full when it is really not so). A suitable grout is composed of 4 parts of stone dust to one part of cement.  When small pieces are put in for such purposes these also should be dowelled where possible and dove tailed into the main block as an additional security.

5.1.11. Seasoning of stones - Stone freshly quarried contains some moisture which is called “quarry sap” particularly in the case of limestone, sandstone and laterites. In this state it is more easily worked.  As the quarry sap evaporates, the stone becomes harder.  It is therefore desirable to expose the stone to open air at least for two seasons before it is used in masonry.

5.1.12. Specification for random rubble stone masonry:

5.1.12.1. Stone - The stone will be of the type specified such as granite, trap, lime stone, sand stone, quartzite, etc. and shall be obtained from the quarries, approved by the engineer.  Stone shall be hard, sound, durable, and free from weathering decay and defects like cavities, cracks, flaws, sand holes, injurious veins, patches of loose or soft materials and other similar defects that may adversely affect its strength and appearance.  As far as possible stone shall be of uniform colour, quality, or texture.  Generally stones shall not contain crystalline silica or chart, Mica and other deleterious materials like iron oxide, organic impurities etc. Stones with round surface shall not be used.

The compressive strength of common types of stones shall be as per Table 1 and the percentage of water absorption shall generally not exceed 5% for stones other than specified in Table 1.  For laterite this percentage is 12%.

Table 1

Type of stone

Maximum Water Absorption percentage by weight

Minimum Compressive strength kg/sq cm

Granite

0.5

1000

Basalt

0.5

400

Lime stone (Slab & Tiles)

0.15

200

Sand stone (Slab & Tiles)

2.5

300

Marble

0.40

500

Quartzite

0.40

800

Laterite (Block)

12

35

Note 1:  Test for compressive strength shall be carried out as laid down in IS: 1121 (Part 1).

Note 2:  Test for water absorption shall be carried out as laid down in IS: 1124.

5.1.12.2. Size of stones - Normally stones used should be small enough to be lifted and placed by hand.  Unless otherwise indicated, the length of stones for stone masonry shall not exceed three times the height and the breadth or base shall not be greater than three-fourth the thickness of the wall, or not less than 15 cm.  The height of stone may be up to 30 cm.

Fig. 1 to 6 – Stone masonry

5.1.12.3. Random Rubble Masonry shall be uncoursed or brought to courses as specified (Fig 7 and 8).  Uncoursed random rubble masonry shall be constructed with stones of sizes as referred and shapes picked at random from the stones brought from the approved quarry.  Stones having sharp corners or round surfaces shall, however, not be used.

5.1.12.4. Random rubble masonry brought to the course is similar to uncoursed random rubble masonry except that the courses are roughly leveled at intervals varying from 30 cm to 90 cm in height according to the size of stones used.

Fig. 7 – Random Rubble Masonry

5.1.12.5. Dressing - Each stone shall be hammer dressed on the face, the sides and bed.  Hammer dressing shall enable the stones to be laid close to neighboring stones such that the bushing in the face shall not project more than 40 mm on the exposed face and 10 mm on the face to be plastered.

Note: Dressing is classified ordinarily as: - Single line, two line, or three line according to the degree of fineness to which they have to be dressed. In single line dressing the maximum projection or depression with reference to the mean plane should not be more than 3 mm, and 1.5 mm in double line and 1 mm in three line dressing.  Dressing of stones finer than three lines dressing is known as pal mane, which is adopted in special cases, and especially where the surfaces are not to the plane desired even after fine dressing.

Fig. 8 – Rubble stone masonry - coursed

5.1.12.6. Mortar - The mortar used for joining shall be as specified.

5.1.12.7. Laying - All stones shall be wetted before use.  Each stone shall be placed close to the stones already laid so that the thickness of the mortar joints at the face is not more than 20 mm.  Face stones shall be arranged suitably to stagger the vertical joints and long vertical joints shall be avoided.  Stones for hearing or interior filling shall be hammered down with wooden mallet into the position firmly bedded in mortar.  Chips or sprawls of stones may be used for filing of interstices between the adjacent stones in heartening and these shall not exceed 20% of the quantity of stone masonry.  To form a bond between successive courses plum stones projecting vertically by about 15 to 20 cm shall be firmly embedded in the heartening at the interval of about one meter in every course.  No hollow space shall be left any where in the masonry.

The masonry work in wall shall be carried out true to plumb or to specified batter.

Random rubble masonry shall be brought to the level course at plinth, windowsills, lintel and roof levels.  Leveling shall be done with concrete comprising of one part of the mortar as used for masonry and two parts of graded stone aggregate of 20 mm nominal size.

The masonry in structure shall be carried out uniformly.  Where the masonry of one part is to be delayed, the work shall be raked back at an angle not steeper than 45 degree.

5.1.12.8. Bond stones - Bond or through stones running right through the thickness of walls, shall be provided in walls up to 60 cm thick and in case of wall above 60 cm thickness, a set of two or more bond stones overlapping each other by at least 15 cm shall be provided in a line from the face of the wall to the back. In case of highly absorbent types of stones (porous lime stone and sand stone etc.) single piece bond stones may give rise to dampness. For all thickness of such walls, a set of two or more bond stones overlapping each other by at least 15 cm shall be provided.  Length of each such bond stone shall not be less than two-third of the thickness of the wall.

Where bond stones of suitable lengths are not available precast cement concrete block of 1:3:6 mix (1cement : 3 coarse sand : 6 graded stone aggregate 20 mm nominal size) of cross section not less than 225 square centimeters and length equal to the thickness of wall shall be used in lieu of bond stones.  (This shall be applicable only in masonry below ground level and where masonry above ground level is finally required to be plastered). At least one bond stone or a set of bond stones shall be provided for every 0.5 sq m of the area of wall surface.  All bond stones shall be marked suitably with paint as directed by the engineer.

5.1.12.9. Quoin and jamb stones - The quoin and jamb stones shall be of selected stones neatly dressed and hammer or chisel to form the required angle.  Quoin stones shall not be less than 0.01 cum in volume.  Height of quoins and jamb stones shall not be less than 15 cm.. Quoins shall be laid header and stretcher alternatively.

5.1.12.10. Joints - Stone shall be so laid that all joints are fully packed with mortar and chips.  Face joints shall not be more than 20 mm thick.

The joints shall be struck flush and finished at the time of laying when plastering or pointing is not to be done.  For the surfaces to be plastered or pointed, the joints shall be raked to a minimum depth of 20 mm when the mortar is still green.

5.1.12.11. Scaffolding - Single scaffolding having one set of vertical support shall be allowed.  The supports shall be sound and strong, tied together by horizontal pieces, over which the scaffolding planks shall be fixed.  The inner end of the horizontal scaffolding member may rest in a hole provided in the masonry.  Such holes, however, shall not be allowed in pillars under one meter in width or near the skew back of arches.  The holes left in masonry work for supporting scaffolding shall be filled and made good with cement concrete 1:3:6 (1 cement : 3 coarse sand : 6 stone aggregate 20 mm nominal size).

5.1.12.12. Curing - Masonry work in cement or composite mortar shall be kept constantly moist on all faces for a minimum period of seven days.  In case of masonry with fat lime mortar curing shall commence two days after laying of masonry and shall continue for at least seven days thereafter.

5.1.12.13. Protection - Green work shall be protected from rain by suitable covering.  The work shall also be suitably protected from damage, mortar dropping and rain during construction.

5.1.12.14. Measurements

5.1.12.14.1 The length, height and thickness shall be measured correct to a cm.  The thickness of wall shall be measured at joints excluding the bushing.  Only specified dimensions shall be allowed; anything extra shall be ignored.  The quantity shall be calculated in cubic metre nearest to two places of decimal.

5.1.12.14.2. The work under the following categories shall be measured separately.

  1. From foundation to plinth level (level one): (a) Work in or under water and /or liquid mud, (b) Work in or under foul positions.
  2. From plinth level (Level one) to floor two level.
  3. From floor two levels to floor three level and so on.
  4. Stone masonry in parapet shall be measured together with the corresponding item in the wall of the storey next below.

Note :( 1) Floor I is the lowest floor above ground level in the building unless otherwise specified in a particular case.  The floors above floor 1 shall be numbered in sequence as floor 2, floor 3 and so on.  Number will increase upwards. (2)  For floor 1, top level of finished floor shall be the floor level and for all other floors above floor   1, top level of structural slab shall be the floor level. (3) Floor level or 1 or 1.2 m above the ground level whichever is less shall be the plinth level.

5.1.12.14.3. No deduction shall be made nor extra payment made for the following

  1. Ends of dissimilar materials (that is joists, beams, lintels, posts, girders, rafters purlins, trusses, corbels, steps etc.) up to 0.1 sqm in section.(ii)Openings each up to 0.1 sqm in area. In calculating the area of openings, any separate lintels or sills shall be included along with the size of opening but the end portions of the lintels shall be excluded and the extra width of rebated reveals, if any, shall also be excluded. (iii) Wall plates and bed plates, and bearing or chajjas and the like, where the thickness does not exceed 10 cm and the bearing does not extend over the full thickness of the wall.

Note: The bearing of floor and roof shall be deducted from wall masonry. (iv) Drain holes and recess for cement concrete blocks to embed hold fasts for doors, windows, etc.(v) Building in masonry, iron fixture, pipes up to 300 mm dia, hold fasts of doors and windows etc. (vi)Forming chases in masonry each up to section of 350 sq cm.

Masonry (excluding fixing brick work) in chimney breasts with smoke of air flues not exceeding 20 sq dm (0.20 sq m) in sectional area shall be measured as solid and no extra payment shall be made for pargetting and coring such flues.  Where flues exceed 20 sq dm (0.20 sq m) sectional area, deduction shall be made for the same and pargetting and coring flues shall be measured in running meters stating size of flues and paid for separately.  Aperture for fire place shall not be deducted and no extra payment made for splaying of jambs and throatings.

5.1.12.14.4. Apertures for fireplaces shall not be deducted and extra labour shall not be measured for splaying of jambs, throating and making arch to support the opening.

5.1.12.14.5. Square or rectangular pillars - These shall be measured as walls, but extra payment shall be allowed for stone work in square or rectangular pillars over the rate for stone work in walls.  Rectangular pillar shall mean a detached masonry support rectangular in section, such that its breadth does not exceed two and a half times the thickness.

5.1.12.14.6. Circular pillars (columns) - These shall be measured as per actual dimensions, but extra payment shall be allowed for stone work in circular pillars over the rate for stone work in walls.  The diameter as well as length shall be measured correct to a cm.

5.1.12.14.7. Tapered walls - shall be measured net, as per actual dimensions and paid for as other walls.

5.1.12.14.8. Curved masonry - Stone masonry curved on plan to a mean radius exceeding 6 meters shall be measured and included with general stone work.  Stone work circular on plan to a mean radius not exceeding 6 meters shall be measured separately and shall include all cuttings and waste and templates.  It shall be measured as the mean length of the wall.

5.1.12.15. Rate - The rate shall include the cost of materials and labour required for all the operations described above and shall include the following:

  1. Raking out joints for plastering or pointing done as a separate item, or finishing flush as the work proceeds. (b)Preparing tops and sides of existing walls for raising and extending.(c) Rough cutting and waste for forming gables cores, skew backs or spandrels of arches, splays at eaves and all rough cutting in the body of willing unless otherwise specified.(d) Bond stones or cement concrete bond blocks. (e) Leading and making holes for pipes etc. (f) Bedding and pointing wall plates, lintels, sills etc., in or on walls, bedding roof tiles and corrugated sheets in or on walls.(g) Building in ends of joists, beams, lintels etc.

5.1.13. SPECIFICATIONS FOR COURSED RUBBLE MASONRY FIRST SORT (FIG. 9)

5.1.13.1. Stone: Shall be as specified in 5.1.12.1

5.1.13.2. Size of Stone: Shall be as specified in 5.1.12.2

5.1.13.3. Dressing - Face stones shall be hammer dressed on all beds, and joints so as to give them approximately rectangular block shape.  These shall be squared on all joints and beds.  The bed joint shall be rough chisel dressed for at least 8 cm back from the face, and side joints for at least 4 cm such that no portion of the dressed surface is more than 6 mm from a straight edge placed on it.  The bushing on the face shall not project more than 4 cm as an exposed face and one cm on a face to be plastered.  The hammer dressed stone shall also have a rough tooling for minimum width of 2.5 cm along the four edges of the face of the stone, when stone work is exposed.

5.1.13.4. Mortar - The mortar for jointing shall be as specified.

5.1.13.5. Laying - All stones shall be wetted before use. The walls shall be carried up truly plumb or to specified batter. All courses shall be laid truly horizontal and all vertical joints shall be truly vertical.  The height of each course shall not be less than 15 cm nor more than 30 cm.

Face stones shall be laid alternate headers and stretchers.  No pinning shall be allowed on the face.  No face stone shall be less in breadth than its height and at least one third of the stones shall tail into the work for length not less than twice their height. The hearting or the interior filling of the wall shall consist of stones carefully laid on their proper beds in mortar ; chips and spalls of stone being used where necessary to avoid thick beds of joints of mortar and at the same time ensuring that no  hollow spaces are left anywhere in the masonry.  The chips shall not be used below the hearting stone to bring these up to the level of face stones.  The use of chips shall be restricted to the filling of interstices between the adjacent stones in hearting and these shall not exceed 10% of the quantity of stone masonry. The masonry in a structure shall be carried up uniformly but where breaks are unavoidable, the joints shall be raked back at angle not steeper than 45 degree.  Toothing shall not be allowed.

5.1.13.6. Bond stones - Shall be as specified except that a bond stone or a set of bond stones shall be inserted 1.5 to 1.8 meters apart, in every course.

5.1.13.7. Quoins - The quoins shall be of the same height as the course in which these occur.  These shall be at least 45 cm long and shall be laid stretches and headers alternatively. These shall be laid square on the beds, which shall be rough-chisel dressed to a depth of at least 10 cm.  In case of exposed work, these stones shall have a minimum of 2.5 cm wide chisel drafts at four edges, all the edges being in the same plane.

5.1.13.8. Joints - All bed joints shall be horizontal and all side joints vertical.  All joints shall be fully packed with mortar, face joints shall not be more than one cm thick.

When plastering or pointing is not required to be done, the joints shall be struck flush and finished at the time of laying.  Otherwise, joints shall be raked to a minimum depth of 20 mm by raking tool during the progress of work, when the mortar is still green.

5.1.13.9. Curing, scaffolding, measurements and rates - Shall be as specified under 5.1.12

5.1.14. SPECIFICATIONS FOR COURSED RUBBLE MASONRY – SECOND SORT (FIG. 8):-

5.1.14.1. Stone - Shall be as specified in 5.1.12.1

5.1.14.2. Size of stone - Shall be as specified in 5.1.12.2

5.1.14.3. Dressing - Shall be as specified in 5.1.13.3 except that no portion of dressed surface shall exceed 10 mm from a straight edge placed on it.

5.1.14.4. Mortar - The mortar for jointing shall be as specified.

5.1.14.5. Laying - Shall be as specified in 5.1.13.5 except that the use of chips shall not exceed 15% of the quantity of stone masonry and stone, in each course need not be of the same height but not more than two stones shall be used in the height of a course.

5.1.14.6. Bond stone, quoins - Shall be as specified in 5.1.13.6 and 5.1.13.7

5.1.14.7. Joints - All bed joints shall be horizontal and all side vertical.  All joints shall be fully packed with mortar, face joints shall not be more than 2 cm thick.

When plastering or pointing is not required to be done, the joints shall be struck flush and finished at the time of laying.  Otherwise, the joints shall be raked to a minimum depth of 20 mm by raking tool during progress of work, where the mortar is still green.

5.1.14.8. Curing, scaffolding, measurement and rates - Shall be as specified in 5.1.12

5.1.15. SPECIFICATIONS FOR PLAIN ASHLAR MASONRY (FIG. 9)

5.1.15.1. Stone shall be of the type specified.  It shall be hard, sound, durable and tough, free from cracks, decay and weathering and defects like cavities, cracks, flaws, sand holes, veins, patches of soft or loose materials etc. Before starting the work, the contractor shall get the stones approved by engineer.

5.1.15.2. Size of stone - Normally stones used should be small enough to be lifted and placed by hand.  The length of the stone shall not exceed three times the height and the breadth on base shall not be greater than three – fourth of the thickness of wall not less than 15 cm.  The height of stone may up to 30 cm.

5.1.15.3. Dressing - Every stone shall be cut to the required size and shape, so as to be free from waviness and to give truly vertical and horizontal joints.  In exposed masonry, the faces that are to remain exposed in the final position and the adjoining faces to a depth of 6 mm shall be the fine chisel dressed so that when checked with 60 cm straight edge, no point varies from it by more than 1 mm.  The top and bottom faces that are to form the bed joints shall be chisel dressed so that variation from 60 cm straight edge at no point exceeds 3 mm.  Faces which are to form the vertical joints should be chisel dressed so that variation at any point with 60 cm straight edge does not exceed 6 mm. Any vertical face that is to come against backing of masonry shall be dressed such that variation from straight edge does not exceed 10 mm. All angles and edges that are to remain exposed in the final position shall be true, square and free from chippings. A sample of dressed stone shall be prepared for approval of engineer.  It shall be kept at the worksite as a sample after being approved.

5.1.15.4. Mortar - The mortar for jointing shall be as specified.

5.1.15.5. Laying - All stones shall be wetted before placing in position.  These shall be floated on mortar and bedded properly in position with wooden mallets without the use of chips or under pinning of any sort. The walls and pillars shall be carried up truly plumb or battered as shown in drawings.  All courses shall be laid truly horizontal and all vertical joints shall be truly vertical.

In case of ashlar work without backing of brick work or coursed rubble masonry, face stone shall be laid headers and stretchers alternatively unless otherwise directed.  The headers shall be arranged to come as nearly as possible in the middle of stretchers above and below.  Stone shall be laid in regular courses of not less than 15 cm in height and all the courses shall be of same height, unless otherwise specified. For ashlar facing with backing of brick work or coursed rubble masonry (See Fig. 10) face stone shall be laid in alternate courses of headers and stretches unless otherwise directed.  Face stone and bond stone course shall be maintained throughout.  All connected masonry in a structure shall be carried up nearly at one uniform level throughout, but where breaks are avoidable, the joint shall be made in good long steps so as to prevent cracks developing between new and old work.  Bond stone provided in the masonry shall be payable in the item of ashlar masonry.  Neither any deduction will be made from the brick masonry for embedding the bond stone in neither the backing nor any extra payment shall be made for any extra labour involved in making holes in brick masonry backing. When necessary, jib crane or other mechanical appliances shall be used to hoist the heavy pieces of stones and place these into correct positions, care being taken that the corners of the stone are not damaged.  Stone shall be covered with gunny bags, before tying chain or rope is passed over it, and it shall be handled carefully.  No piece which has been damaged shall be used in work.

5.1.15.6. Bond stones - Shall be as specified in 5.1.12.8.

5.1.15.7. Joints - All joints shall be full of mortar.  These shall be not more than 6 mm thick.  Face joints shall be uniform throughout and a uniform recess of 20 mm depth from face shall be left with the help of the steel plate during the progress of work.

5.1.15.8. Pointing - All exposed joints shall be pointed with mortar as specified.  The pointing when finished shall be sunk from stone face by 5 mm or as specified.  The depth of mortar in pointing work shall not be less than 15 mm.

Fig. 9 – Ashlar stone masonry

5.1.15.9. Curing - Masonry work in cement or composite mortar shall be kept constantly moist on all faces for a minimum period of seven days.  In case of masonry with fat lime mortar, curing shall commence two days after laying of masonry and shall continue for at least seven days thereafter.

5.1.15.10. Protections - Green work shall be protected from rain by suitable covering.  The work shall also be suitably protected from damage, mortar dropping and rain during construction.

5.1.15.11. Scaffolding - Double scaffolding having two sets of vertical supports shall be provided.  The supports shall be sound and strong, tied together with horizontal pieces over which scaffolding planks shall be fixed.

5.1.15.12. Measurements - The finished work shall be measured correct to a centimeter in respect of length, breadth and height. The cubical contents shall be calculated in cubic meter nearest to two places of decimal.

Fig. 10 – Ashlar stone masonry (with brick backing)

5.1.15.12.1. No deduction nor any extra payment shall be made for the following:

(1)Ends of dissimilar materials (that is joists, beams, lintels, posts, girders, rafters, purlins, trusses, corbels, steps etc.) up to 0.1 sqm in section. (2)Openings up to 0.1 sqm in area.  In calculating the area of opening, any separate lintels or sills shall be included along with the size of the opening but

the end portion of the lintels shall be excluded and extra width of rebated reveals, if any, shall also be excluded. (3) Wall plates and bed plates and bearing of chajja and the like, where the thickness does not exceed 10 cm and the bearing does not extend over the full thickness of the wall.

Note: The bearing of floor and roof slabs shall be deducted from wall masonry.

  1. Drainage holes and recesses left for cement concrete blocks to embed hold-fasts for doors and windows, building in the masonry iron fixture and pipes up to 300 mm diameter.
  2. Stone walls in chimney breasts, chimney stacks, smoke or air flues not exceeding 0.20 sqm in sectional area shall be measured as solid and no extra measurement shall be made for pargetting and coring such flues.  Where flues exceed 0.20 sqm in sectional area, deduction shall be made for the same and pargetting and coring flues paid for separately.

5.1.15.12.2. Square, rectangular or circular pillars - Shall be measured and paid for as walls, but extra payment shall be allowed for such pillars and columns over the rate for stone work in walls.

Rectangular pillars shall mean a detached masonry support, rectangular in section, such that its breadth shall not exceed two and half times the thickness.

5.1.15.12.3. Curved stone work - Stone work curved on a plan to a mean radius exceeding six meters shall be measured net and included with general stone work.  Stone work circular on a plan to a mean radius not exceeding six meters shall be measured separately and extra payment shall be allowed and shall include all cutting and waste and templates.  It shall be measured as the mean length of wall.

5.1.15.13. Rate - The rate shall include the cost of materials and labour required for all the operations described above.  Stone facing or wall lining up to and not exceeding 8 cm thickness shall be paid for under “Stone work for wall lining etc. (Veneer work)”.  The stone work of thickness exceeding 8 cm shall be paid under relevant items of work.

5.1.16. SPECIFICATIONS FOR PUNCHED ASHLAR (ORDINARY) MASONRY

5.1.16.1. Stone - Shall be as specified in 5.1.15.1

5.1.16.2. Size of stone - Shall be as specified in 5.1.15.2

5.1.16.3. Dressing - Shall be as specified in 5.1.15.3 except that the faces exposed in view shall have a fine dressed chisel draft 2.5 cm wide all round the edges and shall be rough tooled between the drafts, such that the dressed surface shall not be more than 3 mm from a straight edge placed over it.

5.1.16.4. Other details - The specifications for mortars, laying and fixing, bond stone, joints, pointing, curing, protections, scaffolding, measurements and rates shall be same as specified in 5.1.15.

5.1.17. SPECIFICATIONS FOR MOULDED, SUNK, CARVED ASHLAR MASONRY (FIG. 11)

5.1.17.1. Stone - Shall be as specified in 5.1.15.1

5.1.17.2. Dressing 

5.1.17.2.1. Every stone shall be cut to the required size and shape and chisel dressed on all beds and joints so as to be free from any waviness and to give perfectly vertical, horizontal, radial or circular joints with adjoining stones as the case may be.  The dressed surface shall not be more than 3 mm from a straight edge placed on it. The face shall be gauged, cut, chamfered, grooved, rebated sunk or plain moulded and fine tooled as shown in the working drawings.  The joints 6 mm from the face shall also be fine tooled so that straight edge laid along it is in contact with every point.  It shall be finest surface, which can be given to a stone with the chisel and without rubbing.

In case of sunk or moulded masonry, the corner stone shall be dressed at true right angles or true to the shape as specified. The corners being straight and vertical. For arch (See Fig. 12), dome or circular work (See Fig. 12) the stone shall be dressed to require wedge shape so that joints shall be truly radial.

5.1.17.2.2. Sample - The full size layout of the moulding etc. shall be prepared on platform from which sheet templates shall be cut and the stone dressed to templates to a uniform and fine finish.  All visible angles and edge shall be True Square and free from chippings.  A sample of dressed stone shall be prepared for approval and it shall be kept as sample after being approved by engineer.

Fig. 11 – Moulded, sunk, carved stone work

In case of ashlar moulded and carved columns a full size model of the required moulding, carving etc. shall be prepared in plaster of Paris and kept at site of work as sample work after being approved by the engineer.  The stones shall be moulded and carved in accordance with the approved model to a uniform and fine finish.

5.1.17.3. Other details - Shall be as specified in 5.1.15.4, 5.1.15.5, 5.1.15.6, 5.1.15.7, and 5.1.15.11

5.1.17.4. Centering and shuttering - Centering and shuttering required for arch dome or circular moulded work shall be constructed as directed by the engineer.

5.1.17.5. Measurements - The dimensions of the circumscribing rectangles of the dressed stone used in the work shall be measured correct to a cm and cubical contents shall be calculated in cubic metres, nearest to two places of decimal.

Fig. 12 – Stone work in Arches & Chajja

In case of sunk or moulded work the measurements for the work shall be taken course by course.  The plain stone used in conjunction with sunk or moulded stone shall be measured and paid for under the relevant item of stone work. Sunk or moulded work in rectangular, square and circular pillars, moulded cornices and string courses shall be measured under stone work sunk or moulded but extra payment shall be allowed over the general work in each case.  No such extra payment shall be allowed for moulded string and plinth courses. In case of arch dome or circular moulded work for arches exceeding six metres in clear span extra payment for additional cost of centering shall be made on the actual area of soffit including strutting, bolting, wedging, easing, striping and removal.

5.1.17.6. Rate - The rate includes the cost of all materials and labour involved in all the operations described   above, including centering and shuttering for arch, dome or circular moulded work.

5.1.18. SPECIFICATIONS FOR STONE VENEERING WORK (FIG. 13, 14 & 15)

Stone lining up to 8 cm shall be treated as veneering work and lining of greater thickness as plain Ashlar Masonry.

5.1.18.1. Stone - Shall be as specified in 5.1.15.1.

The stone shall be cut into slabs of required thickness along the planes parallel to the natural bed of stone.

5.1.18.2. Dressing - Shall be as specified in 5.1.15.3 excepting that dressing at the back shall not be done, so as to better grip with the hearting or backing.  The dressed slabs shall be of the thickness as specified, with permissible tolerance of 2 mm.

5.1.18.3. Mortar - Mortar for fixing shall be as specified.

5.1.18.4. Laying - The stone shall be wetted before laying.  They shall then be fixed with mortar in position without the use of chips or under pinning of any sort. Where so desired, the adjoining stones shall be secured to each other by means of copper pins 75 mm long and 6 mm diameter or as specified.

Fig. 13 – Stone veneering

Further the stones shall be secured to the backing by means of cramps.  The material for cramps shall have high resistance to corrosion under conditions of dampness and against the chemical action of mortar of concrete in which cramps are usually embedded.

Cramps shall be of 25 mm x 6 mm and 30 cm long in case of backing of stone masonry walls and brick masonry walls thickness than 230 mm.  In case of backing, with brick masonry wall 230 mm or less thick or RCC members, cramps shall be of 25 x 6 mm and length as per requirement made out of

Fig. 14 – Stone veneering – Typical fixing arrangement

directed by the engineer if so, required at site.  Cramps shall be spaced not more than 60 cm apart horizontally.

Fig. 15 – General arrangements of cramps

Alternatively the stone may be secured to the backing by means of stone dowels 10 x 5 x 2.5 cm as per shape indicated in Fig. 14 and the adjoining stone secured to each other by means of gun metal cramps or copper pins of the specified size. Minimum one cramp /stone dowel shall be used to secure one slab to the backing.

Cramps may be attached to its sides (see Fig 15A, 15B) or top and bottom (see Fig. 15C to F) or sides, top and bottom (see Fig. 15 G & H). The minimum numbers of cramps required for fixing facing unit to the wall are illustrated in Fig. 15. The actual number of cramps and their sections, however, shall be as per requirements of design to carry the loads.

Where cramps are used to hold the unit in position only, the facings shall be provided with a continuous support on which the stones rest at the ground level and other storey levels, the support being in the form of projection from or recess into the concrete floor slab, or a beam between the columns or a metal angel attached to the floor slab or beams. These supports shall preferably be at vertical intervals not more than 3.5 m apart and also over the heads of all openings.  Such supports shall also be provided where there is transition from thin facings below to thick facings above.

Alternatively cramps may be used to hold the units in position and in addition to support the units thus transferring the weight of the units to the backing. Such cramp should be properly designed as per IS: 4101(Part 1). The cramps may be of gun metal or copper alloyed with zinc, tin, nickel, lead and /or stainless steel. The pins, cramps and dowels shall be laid in cement mortar 1:2 and their samples got approved by the engineer and kept at site.

The walls shall be carried up truly plumb.  All courses shall be laid truly horizontal and all vertical joints truly vertical.  The stone shall break joints on the face for at least half the height of the course, unless otherwise shown in the drawings.  The stone shall be laid in regular courses not less than 20 cm height and all the stones shall be of the same height unless otherwise specified.  No stone shall be less in length than one and a half times to height unless otherwise specified.

As far as possible the backing shall be carried up simultaneously with the face work. In case of reinforced cement concrete backing, the limit shall be secured to the backing after it has set got cured. The cramps shall be fixed in concrete to the required positions, while laying.

5.1.18.5. Joints - The joints shall be done with composite cement lime mortar 1:1:6.  All joints shall be full of mortar. Special care shall be taken to see that the grounding for veneer work is full of mortar.  If any hollow grounding is detected by taping the face stones, these shall be taken out and relaid. The thickness of joints shall be as small as possible, not exceeding 5 mm.  For a close butt jointed facing the thickness shall not exceed 1.5 mm.  The face joints shall be uniform throughout.

Where joint filler or compound is to be used, the joints shall be raked out to a depth of at least 25 mm after the mortar in the joints has set sufficiently and the filler or compound applied. The joints may be subsequently finished with a mortar suited to the appearance of the work.  It is preferable to use joint sealing compounds where the facings are exposed to heavy rainfall and winds and their selections would depend upon local experience and availability of joint sealing compounds.  In their absence only masonry mortars 1:1:6 which are proved to be successful from local exposure conditions shall be used.

5.1.18.6. Other details - Specifications for pointing, curing, protections and scaffolding shall be as specified in 5.1.15.4

5.1.18.7. Measurements - The length and breadth of the finished work shall be measured in meter correct to cm. The area should be calculated in sq. meter correct to two places of decimal. The veneering work curved on plan shall be measured as plain work, but extra payment shall be allowed for radii not exceeding six meters on external face.  For radii beyond six meters the work shall be measured as plain work only, even the face may have to dress to curve.

5.1.18.8. Rate - The rate includes the cost of materials and labour involved in all the operations described above, except for the cost of providing and fixing pins, dowels and metal cramps and ledges and supports, which shall be paid for separately unless otherwise stipulated in the item of work.

5.1.19. SPECIFICATIONS FOR STONE CHAJJA (FIG. 13)

5.1.19.1. Stone slabs shall be hard, sound and durable.  These shall be chisel dressed on all faces which are exposed to view and rough dressed at other surface.  Angles shall be true and edge lines straight.  The finished thickness shall be as stipulated with permissible tolerance of ± 2 mm.  The length of stone slabs in Chajja shall not be less than 60 cm unless otherwise specified.

5.1.19.2. In case of sloping Chajja the stone shall be sloped as specified. It shall have minimum bearing of 20 cm measured horizontally on the wall and the bearing shall also be similarly sloped.  Each slab shall have a hole in the centre of the bearing area through which the anchoring M. S. holding down bolt shall pass.  The holding down bolts shall be 12 mm diameter and shall be bent at right angles at its lowest end and buried horizontally for at least 7 cm in a joint 30 cm below the bearing surface.  Each holding down bolt shall be secured at top by suitable washer and nut.

The chajjas shall be provided with cove supports, where cove is in brick masonry, it shall project out from the wall as under.

1).45 cm wide Chajja, cove projection 15 cm, depth of cove 3 courses.

2).60 cm wide Chajja, cover projection 20 cm, depth of cove 4 courses.

3).75 cm wide Chajja, cove projection 25 cm, depth of cove 5 courses.

4).90 cm wide Chajja, cove projection 30 cm, depth of cove 6 courses.

5.1.19.3. In case of horizontal Chajja, the stone shall be fixed horizontally with the slight outer slope of about 1 cm.  It shall have minimum bearing of 15 cm on the wall.  Holding down bolts shall be provided, only where so specified.

5.1.19.4. Pointing - The joints shall be pointed with 1:2 cement mortars (1cement: 2 stone dust) with an admixture of pigment to match the stone shade; and properly cured.

5.1.19.5. Other details - Specifications for curing, protections and scaffolding shall be as specified.

5.1.19.6. Measurements - The length and breadth of the finished work shall be measured correct to a cm.  The area of Chajja projecting beyond the wall shall be calculated in sqm correct to two places of decimal. In case of sloping Chajja, the sloping breadth shall be measured correct to a cm and the area of Chajja projecting beyond the wall shall be calculated in sqm correct to two places of decimal.

5.1.19.7. Rate - The rate shall include the cost of all materials and labour involved in all the operations described above.  Anchoring the coves shall be deemed to be included in the rate, only when it is so stipulated in the description of the item.

5.1.20. SPECIFICATIONS FOR SHELVES, COPING, PLAIN, CORNICES & STRING COURSES ETC.

5.1.20.1. Stone - Stone shall be of uniform colour and texture and of the kind as stipulated.

5.1.20.2. Dressing - The exposed faces and sides of shelves shall be chisel dressed such that the dressed surface shall not be more than 3 mm from a straight edge placed on it.  All visible angles and edges shall be free from chippings.  The surfaces to be buried in the masonry shall be rough dressed.

5.1.20.3. Laying - These shall be laid in mortar of specified mix and fixed as shown or as directed by the engineer.

5.1.20.4. Other details - Specifications for pointing, curing protections and scaffolding shall be as specified in 5.1.15.

5.1.20.5. Measurements

5.1.20.5.1. Shelves - The length and breadth shall be measured inclusive of bearings correct of a cm.  The thickness shall be as specified with permissible tolerance of + 2 mm.  The area shall be calculated in sqm correct to two places of decimal.

5.1.20.5.2. Copings - The dimensions of the circumscribing rectangles of the dressed stones as used in work shall be measured correct to a cm.  The cubical contents shall be calculated correct to two places of decimal in cu. m.

5.1.20.5.3. Plain cornices, string courses and plinth courses - The length, breadth and depth of the stone including bearing shall be measured correct to a cm.  The cubical contents shall be calculated correct to two places of decimal in cu. m.

No deduction shall be made from the masonry of wall for the bearing of stone shelves, cornices, string courses.

5.1.20.6. Rate - The rate shall include the cost of all materials and labour required in all the operations described above.

5.1.21. SPECIFICATIONS FOR STONE JALI

5.1.21.1. Stone - Shall be as specified in 5.1.15.1.

5.1.21.2. Dressing and fixing - The stone shall be cut into slabs of required thickness so as to make jali of the specified thickness.  The jali shall be cut as per pattern shown on the drawings.  All exposed faces shall be fine tooled to a uniform and smooth finish.  Fixing shall be done with the adjoining work in grooves, rebates etc., as shown in the drawing or as directed by the engineer.  A tolerance of +/- 2 mm shall be allowed in the specified thickness of the jali.

5.1.21.3. Measurements - The length and breadth of the stone forming the jali including its borders shall be measured correct to a cm and the area shall be calculated in square metres nearest to two places of decimal.

5.1.21.4. Rate - It includes the cost of labour and materials required for all the operation described above.  It also includes the cost of making grooves or rebates in the adjoining work for fixing jali.

5.1.22. SPECIFICATIONS FOR LATERITE STONE MASONRY

5.1.22.1. Laterite stone should be compact in texture.  It may be mottled with streaks of brown, red and yellow colours. It should not contain white clay or lithomarge or an appreciable number of deep sinuosity. Blocks should be obtained from a good ferruginous variety of laterite which hardens on exposure after it is quarried.

5.1.22.1.2. Stones should be dressed immediately after quarrying into regular rectangular blocks, so that all faces are free from waviness and edges are straight and square.  Blocks may be cut to size manually or by machine; for good quality work machine cut blocks may be used. Stone blocks after dressing shall be exposed to atmosphere for a period of 3 months before use in masonry.  The stone, on exposure changes its nature and improves in compressive strength.

5.1.22.1.3. Blocks are laid in masonry in regular horizontal courses, breaking bond of vertical joints in every course to the extent of half the height of blocks.  When the thickness of a masonry element is more than the breadth, these should be laid as headers and stretchers as in English bond.

5.1.22.1.4. Joint thickness shall not be more than 10 mm. Faces may be plastered, pointed or finished flush. Joints should be raked to a depth of 15 mm for pointing, while the mortar is green.

5.1.22.2. Dressing - Laterite stones shall be hammer dressed into rectangular blocks so that all faces are free from waviness and unevenness, and the edges are true and square.  The least thickness / breadth shall be not less than height.  The length shall generally be equal to twice the breadth, unless otherwise specified.

5.1.22.3. Laying - The dressed stones shall be laid in regular courses of not less than 15 cm height.  All courses in the masonry shall be of the same height unless otherwise directed.  The stones shall be laid in alternate header stretcher fashion, alternative courses of header and stretchers or in any other suitable fashion as directed.  The vertical joints shall break by at least 65 mm.  No specific corner stones are necessary. Quoin may be provided, where so indicated.

5.1.22.4. Joints - All bed joints shall be truly vertical; the thickness of joints shall not exceed 15 mm.  Each stone shall be carefully laid in place with joints completely filled with mortar.  On faces, where no plastering or pointing is required to be done, the joints shall be struck flush as the work proceeds.   In other cases, joints shall be raked square to a minimum depth of 15 mm by a raking tool during the progress of 15 mm by a racking tool during the progress of work while the mortar is still green.

5.1.22.5. Scaffolding, curing and protection - Same as in 5.1.15 shall apply.

5.1.22.6. Measurements and rates - Same as in 5.1.15 shall apply.

5.1.23. SPECIFICATIONS FOR SLATE STONE MASONRY

5.1.23. Slate stone - shall be obtained from the approved quarry, as indicated, and shall not be less than 5 cm thick.  Slate stones shall be carefully hammered down into place with wooden mallet and

firmly bedded with mortar.  Chips and spalls shall be wedged in to avoid thick bed joints of the mortar.  Thickness of mortar in beds and joints shall not exceed 25 mm.  No face work shall be provided.

5.1.23.1. Slate stone masonry shall be built uncoursed. Walls shall be leveled up at the top of plinth, sill and lintel level of openings and at top with minimum amount of chips and spalls. For walls up to 45 cm thick, 25% of face area shall be of bond stones.  For walls over 45 cm thick, 10% of face area shall be of bond stones.  Quoin and jambs stones shall be laid headers and stretchers alternatively.

5.1.23.2. Scaffolding, curing and protection - These shall be as specified in 5.1.15.

5.1.23.3. Measurement and rate - These shall be as specified in 5.1.15.

5.2. SPECIFICATIONS FOR MARBLE WORK

Marble shall be hard, sound, dense and homogeneous in texture with crystalline texture as far as possible.  It shall generally be uniform in colour and free from stains, cracks, decay and weathering.

Marbles are metamorphic rocks capable of taking polish, formed from the re-crystalization of lime stones or dolomitic lime stones and are distinguished from lime stone by even visibly crystalline nature and non flaggy stratification.

Note: Marble is a product of nature hence it is difficult to guarantee uniformity of colour, veining or other characteristics that may be represented in any sample submitted. A sample will indicate only an average of colour, veining and other general texture and specified finish.

5.2.1. Classification - The marble blocks, slabs and tiles shall be classified broadly in the following two categories:

  1. White Marble (2) Coloured Marble such as black, green, pink, brown, grey marble etc.

5.2.1.1. White Marble

Plain White Marble:

  1. Makarana first quality White Marble : Plain white marble without streaks available at chosira pahar Kuwan, Doongri and Bhat.
  2. Makrana second quality White Marble White Marble having lighter shades or spots available at Chosira Pahar Kuwan, Doongri and Lodhi Doongri.
  3. Abu White Marble White Marble with Blue and grey shades available at Ambaji.
  4. Raj Nagar Marble It shall be plain white marble with coarse grains predominantly showing mica particles giving reflection bring in light.

5.2.1.2. Abu panther marbles

White marble with irregular blue black spots available in Ambaji.

5.2.1.3. White veined marbles

  1. Makrana Doongri Adanga Marble :

Light grayish white marble having grey and brown veins available at Doongri and Pahar Kuan.

  1. Makrana  Chak Doongri Marble :

White marble having black streaks available at chak doongri.

  1. Abu White Veined Marble.
  2. White marble with grey or black veins available at Ambaji.
  1. Coloured Marble

5.2.1.4. Black Marble

5.2.1.4.1. Plain black marble

5.2.1.4.2. Black marble sawn along veins locally known as ‘Peta Pasu sawing’ available at   Bhainslana.

Black Zebra Marble: (a) Bhainslana Black Zebra Marble: Black marble having grey or white veins available at Bhainslana. (b) Kishangarh Black Zebra Marble: Black marble with grey and / or white veins available at Kishangarh. (c)Abu Black Zebra Marble: Black marble having white patches and streaks available at Abu.

  1. Narnaul Black Zebra Marbles: Black marble with thin white veins available at Narnaul.
  2. Makrana Dhobi Doongri Zebra Marble: Grayish black marble with white flowery pattern available at Dhobi Doongri.

5.2.1.5 Green marble

  1. Baroda Green Marble: Dark green marble with flowery pattern available at Baroda.
  2. Abu Green Marble: Light green marble with green and /or brown streaks on white ground available at Ambaji.
  3. Falna Green Marble: Green marble with prominent yellowish pattern available at Falna.
  4. Bundi Green Marble: Green marble with pinkish shades available at Umar, (Bundi).

5.2.1.6. Pink marble

5.2.1.6.1 Plain Pink Marble:

Pink Marble with light or dark shades available at Makrana and bar.

5.2.1.6.2. Pink Adanga marble

  1. Makrana Pink Adanga Marble: Pink marble with brown or greenish and white streaks available at Makrana.  It has both light and dark shades of pink.
  2. Bar Pink Adanga Marble: Pink marble with green veins available at Bar.
  3. Bundi Pink Adanga Marble: Pink marble with grey streaks available at Umar (Bundi).

5.2.1.7. Grey marble

  1. Kumari Grey Marble: Grey marble having light blue shades available at Makrana.
  2. Bundi Grey Marble: Grey marble with pink or green or black streaks available at Umar (Bundi).

5.2.1.8. Brown marble

  1. Bar Brown Marble / Brown Marble with light and dark brown shades available at Bar.
  2. Narnaul Brown Marble: Brown marble having teak wood shades available at Narnaul.

5.2.2. Sizes and tolerances

The size of marble blacks’ slabs and tiles shall be as mentioned in Table 1.

Table 1 Sizes of marble blocks, slabs and tiles

 

 

Length

Width

Thickness

1

Blocks

30 to 250

30 to 100

30 to 90

2

Slabs

70 to 250

30 to 100

2 to 15

3

Tiles

10 to 60

10 to 60

0.8 to 2.4

Note 1. All dimensions are in centimeter.

2.  The length and width, of the blocks shall be in multiple of 30 cm.

3.  Length and width of slab shall be in multiple of 10 cm and thickness in multiple of 1 cm.

4.  Tiles shall be square cut and linear dimensions in multiple of 10 cm.

5.  Only slabs and tiles shall be machine cut and factory made.

6.  For 8 mm thick tiles, special precautions will be required for fixing them like using special adhesive as per manufacturer’s specifications.  Such tiles are not suitable for outside veneering work exposed to rains / sun if used in large areas in continuous stretches.  For tiles of thickness 20 mm and above cramps may be provided if approved by the engineer.

Tolerance

The following tolerances shall be allowed in the dimension of blocks, slabs and tiles:

Blocks                                                  Tolerance

a) Length                                            + 2 per cent

b) Width                                             + 2 per cent

c) Thickness                                        + 2 per cent

Slabs

a) Length                                             + 2 per cent

b) Width                                              + 2 per cent

c) Thickness                                       + 3 per cent

Tiles

a) Linear dimension                            + 3 per cent

b) Thickness                                       + 1 per cent

The sizes other than those mentioned above may be provided as directed by the engineer and nothing extra shall be payable on this account.

5.2.3. Physical properties

5.2.3.1. The physical properties of marble for blocks, slabs and tiles and method of tests are mentioned in Table 2.

Table 2 - Physical properties of marble

Characteristic

Requirements

Method of test

1

Moisture absorption after 24 hours Immersion in cold water

Max. 0.4% by weight

IS : 1124*

2

Hardness

Min. 3

Mhos scale

3

Specific gravity

Min. 2.5

IS : 1122#

 Method of test for water absorption of natural building stone.

# Method of determination of specific gravity and porosity of natural building stones.

5.2.3.2. Approval of sample - Before starting the work, the contractor shall get samples of marble approved by the engineer.  Approved samples shall be kept in the custody of the engineer and the marble supplied and used on the work shall conform to samples with regard to soundness, colour, veining and general texture.

5.2.4. Sampling - In any consignment all the blocks/slabs /tiles of the same group, size and finish shall be grouped and tested to constitute a lot.  Sample shall be selected and tested separately for each lot for determining its conformity or otherwise to the requirements of the specification.  The number of blocks/slabs/tiles to be selected for the samples shall depend upon the size of the lot and shall be in accordance with the Table 3.

Table 3 Sample size and criteria for conformity

Number of blocks / sample slabs / tiles in the lot

Number of blocks slabs / tiles to be selected in sample

Permissible number of defectives

Sub Size in No.

Upto 25

3

0

2

26 to 100

5

0

2

101 to 200

8

0

3

201 to 500

13

0

4

501 to 1000

20

1

5

Note: The blocks / slabs / tiles in the sample shall be taken at random and in order to ensure to randomness of selection, random tables may be used.

Explanation 1: All the blocks / slabs / tiles selected in the sample, shall be examined for dimensions workmanship and general requirements. Any block / slab / tile failing in any one or more of the above requirements shall be considered as defective.  A lot shall be considered as conforming to these requirements if the number of defectives obtained is not more than permissible no. of defectives given in Col.3.

Explanation 2: The lot having been found satisfactory with respect to dimensions, workmanship and general requirement shall be tested for physical properties of the marble.  For this purpose a sub sample of the size given in Col. 4 of table 3 shall be selected at random.  These blocks / slabs / tiles in the sub sample shall be tested for moisture absorption, hardness and specified gravity.  The lot shall be considered having satisfied the requirements of the physical properties if none of the blocks/slabs/tiles tested for the requirements fails in any of these tests.

5.2.5. SPECIFICATIONS FOR MARBLE WORK TABLE RUBBED AND POLISHED (PLAIN WORK)

Marble work in steps, jambs, columns and other plain work shall be as specified below.

Joints in staircase treads, kitchen platforms shall be permitted only at curvature or when width / length is more than 0.6 / 2 mtrs respectively.  Number of joints in each direction shall not be more than one number for every 2 mtrs length beyond the initial 2.00 m length.  Additional joints due to curvature or for providing fixture shall be providing judiciously.

5.2.5.1. Dressing and rubbing - Every marble shall be cut to the required size and shape, chisel dressed on all beds and joints, so as to be free from any waviness and to give truly vertical, horizontal, radial or circular joints as required.  The exposed faces and sides of stones forming joints up to 6 mm. from the face shall be fine tooled such that a straight edge laid along the face of the stone is in contact with every point on it.  These surfaces shall then be rubbed smooth.  All visible angles and edges shall be true, square and free from chipping.  Beyond the depth of 6 mm from face, the joints shall be dressed with a slight splay so that the thickness of joint increases, in an inverted V shape.   The surfaces of the stones coming in contact with backing need not be chisel dressed.

A sample of dressed and rubbed stone shall be prepared for approval and it shall be kept on worksite after being approved by the engineer.

5.2.5.2. Mortar - The mortar used for jointing shall be as specified.

5.2.5.3. Laying - All marble stones shall be wetted before placing in position. These shall then be floated on mortar and bedded properly in position with wooden mallets without the use of chips or under pinning of any sort. The walls and pillars shall be carried up truly in plumb or bettered as shown in the drawings.  All courses shall be laid truly horizontal and all vertical joints shall be truly vertical.

In case of work without backing or brick work or coursed rubble masonry, refer Fig. 9.  Face stone shall be laid headers and stretchers alternatively unless otherwise directed.  The headers shall be arranged to come as nearly as possible in the middle of stretchers above and below.  Stone shall be laid in regular courses of not less than 15 cm in height and all courses shall be of the same height unless otherwise specified.

For work facing with backing of brick work or coursed rubble masonry refer Fig. 10. Face stone shall be laid in alternate courses of header and stretchers unless otherwise directed.   Face stone and bond stone courses shall have break joint  on the face of at least half the height of the standard course and the bond shall be masonry in a structure course and the bond shall be carefully maintained through out.  All the connected masonry in a structure shall be carried up nearly at one uniform level throughout but where breaks are unavoidable the joints shall be made in good long steps so as to prevent cracks developing between new and old work.

When necessary jib crane or other mechanical appliances shall be used to hoist the heavy pieces of stones and place these in to correct positions, care being taken that the corners of the stone are not damaged.  Stone shall be covered with gunny bags, before putting chain or rope is passed over it, and it shall be handled carefully.  No piece which has been damaged shall be used in work.  The matching of grains shall be carried out as directed by the engineer.

5.2.5.4. Bond stone - Bond or through stones running right through the thickness of walls, shall be provided in walls up to 60 cm thick and in case of wall above 60 cm thickness a set of two or more bond stones overlapping each other by at least 15 cm shall be provided in a line from face to back.

At least one bond stone or a set of bond stones shall be provided for every 0.5 sq. m. of the wall surface. All bond stones shall be marked suitably as directed by the engineer.

5.2.5.5. Joints - The depth of joints 6 mm from the face shall be uniform and as fine as possible but shall be not more than 1.5 mm thick on the exposed face.  Beyond the depth of 6 mm from face, the thickness of joints shall increase in an inverted V shape so as to give good mortar bond between two stones.  The invented portion of the Joints shall be filled with bedding mortar and the face 6 mm portion with pointing mortar.

5.2.5.6. Curing - The work shall be kept constantly moist on all faces for a period of at least seven days.

5.2.5.7. Finishing - After the marble work is cured, it shall be rubbed with carborundum stone of different grades no, 60, 120 and 320 in successions, so as to give a plane true and highly smooth surface.  It shall be cleaned with a solution of oxalic acid, washed and finished clean.

5.2.5.8. Protection - Green work shall be protected from rain by suitable coverings.  The work shall also be suitably protected from damage during construction.

5.2.5.9. Scaffolding - Double scaffolding having two sets of vertical supports shall be provided where necessary.  The supports shall be sound and strong, tied together by horizontal pieces over which the scaffolding plank shall be fixed.

5.2.5.10. Tolerances:

Note: The above para also applies to the Ashlar masonry referred in Chapter No.7-Stone Work.

5.2.5.11. Measurements - For plain work: Measurements shall be taken correct to a cm.  in length and breadth and correct to 0.5 cm. in thickness.

5.2.5.11.1. In the case of radially dressed or circular stone used in the work, the dimensions of the circumscribing rectangle of the dressed stone shall be measured correct to a centimeter and thickness, correct to 0.5 cm.

The cubical contents shall be calculated in cubic decimeter nearest to two places of decimal.

5.2.5.11.2. The marble work in arches and domes shall be measured as for plain work, but extra shall be allowed for such work over the rate for plain work. 

5.2.5.11.3. Sunk or moulded work in marble shall be measured by volume as per plain marble work or work in arches or domes as the case may be on the basis of circumscribed rectangular block of the finished work but extra shall be paid for such work over the rate for plain work for work in arches and domes.  For the purpose of extra payment, volume of every stone sunk or moulded shall be considered.

5.2.5.12. Rate - The rate includes the cost of materials and labour required for all the operations described above.

5.2.5.13. Use of finished marble slabs and tiles - In case such finished tiles are used, these shall be measured and paid for separately.

5.2.6. Specifications for Marble Wall Lining & Veneer Work

Unless and otherwise specified in the nomenclature of the item, the marble slabs used for wall lining / veneer work shall conform to dimensions given in Table 1 above.

5.2.6.1. Dressing - Dressing shall be same as specified except that the back shall not be dressed, but left rough cut, in order to ensure a good trip with the hearting of backing.  The dressed slabs shall be of the thickness as specified with a tolerance permissible under para above. The tolerance in wall lining when straight edge of 3 m length is placed should not be more than 2 mm.

5.2.6.2. Laying

5.2.6.2.1 The stone shall be wetted before laying.  They shall then be fixed with mortar in position without the use of chips or under pinning of any sort.  Care shall be taken to match the grains of veneer work as directed by the engineer. For purpose of matching the grains, the marble slabs shall be selected judiciously having uniform pattern of veins / streaks. Preferably the slabs shall be on those got out of the same block from the quarry. The area to be veneered shall be reproduced on the ground and the marble slabs laid in position and arranged in the manner to give the desired matching of grains.  Any adjustment needed for achieving the best results shall be then carried out by replacing or interchanging the particular slabs.  Special care shall be taken to achieve the continuity of grains between the two slabs one above the other along the horizontal joints. This shall then be got approved by the engineer and each marble slabs numbered properly and the same number shall be marked on a separate drawing as well as on the surface to be actually veneered, so as to ensure the fixing of the particular slabs in the correct location. For the facing of the columns also the same procedure as mentioned above shall be followed. Where so desired, the adjoining stones shall be secured to each other by means of copper pins 75 mm long and 6 mm diameter or as specified.

Further the stones shall be secured to the backing by means of cramps.  The material of cramps shall have high resistance to corrosion under conditions of dampness and against the chemical action of mortar or concrete in which cramps are usually embedded.

5.2.6.2.2. Cramps shall be of 25 x 6 mm and 30 cm long in case of backing of stone masonry walls and brick masonry walls thicker than 230 mm.  In case of backing with brick masonry walls 230 mm or less thick or RCC members cramps shall be of 25 x 6 mm and length as per requirement made out of gun metal or any other metal as specified in 8.6.2.6 shall be 115 mm and . Generally the outer length of cramp in half brick work backing it shall be 150 mm typical shape & details of cramps for such backing are as indicated in Fig. 16 for general guidance. This can be modified as directed by the engineer if so, required at side.  Cramps shall be spaced not more 60 cm apart horizontally. Alternatively the stone may be secured to the backing by means of stone dowels 10x5x2.5 cm as per shape indicated in Fig. 17.

5.2.6.2.3. The adjoining stone shall be secured to each other by means of gun metal cramps or copper pins of the specified size.  Cramps may be attached to its sides (see Fig. 18A, 18B) or top and bottom (See Fig. 18 C, D, E, F) or sides, top and bottom (see Fig. 18G, 18H). The general arrangement of cramps required for fixing facing unit to the wall are illustrated in Fig. 18.The actual number of cramps and their sections, however, shall be as per requirements of design to carry the loads.

5.2.6.2.4. Where cramps are used to hold the unit in position only, the facings shall be provided with a continuous support on which the stones rest at the ground level and other storey levels, the support being in the form of projection from or recess into the concrete floor slab, or a beam between the columns or a metal angle attached to the floor slab or beams.  These supports shall preferably be at vertical intervals not more than 3.5 m apart and also over the heads of all openings.  Such supports shall also be provided where there is transition from thin facing below to thick facings above.

5.2.6.3. Joints - All joints shall be full of mortar.  Special care shall be taken to see that groundings for veneer work are full of mortar. If any hollow grounding is detected by tapping the face stones, these shall be taken out and re-laid.  The thickness of the face joints shall be uniform, straight and as fine as possible, not more than 1.5 mm and in the face joint, the top 6 mm depth shall be filled with mortar specified for the pointing.

5.2.6.4. Mortar - The mortar used for jointing slabs shall be as specified.

5.2.6.5. Curing, finishing, protection and scaffolding - It shall be as specified in 5.2.5.6 to 5.2.5.9.

5.2.6.6. Measurements - The length and breadth shall be measured correct to a cm.  In case of radially dressed on circular slabs used in the work, the dimensions of the circumscribing rectangles of the dressed stone used in the work, shall be measured & paid for.  The area shall be calculated in sqm nearest to two places of decimal. Marble work in lining up to 4 cm thickness shall be paid by area under veneer work and lining of greater thickness paid by volume under plain marble work.

5.2.6.7. Rate - The rate includes the cost of materials and labour required for all the operations described above except for the cost of providing and fixing of dowel and cramps which shall be paid for separately, unless otherwise stipulated in the item of work.

When factory made finished slabs and tiles are used, no further finishing as mentioned shall be required nor anything extra shall be payable.

5.2.7. Specifications for Marble Jali

Specifications as described under 5.2.5 and 5.2.6 shall apply, so far as these are applicable.

5.2.7.1. The jali shall be of thickness and as per pattern specified.  All exposed faces shall be fine tooled to a uniform and smooth finish. Fixing shall be done with adjoining work in grooves, rebates etc. as shown in the drawings or as specified by the engineer.  Tolerance of + 2 mm shall be allowed in the specified thickness.

5.2.7.2. Measurements - The length and breadth forming the jali including its border, shall be measured correct to a cm.  The area shall be calculated in square metre nearest to two places of decimal.

5.2.7.3. Rate - It includes the cost of labour and materials involved in all the operations described above.  It also includes the cost of making grooves or rebates in the adjoining work for fixing jali.

Fig. 16 Typical details of cramps for R.C.C. Backing

5.3. SPECIFICATIONS FOR PRECAST CONCRETE STONE BLOCKS MASONRY

5.3.0. Terminology - For the purpose of this standard, the following definitions shall apply:

Block density – The density calculated by dividing the mass of a block by the over all volume including holes or cavities.

Stone spalls – Broken stone pieces of varying sizes obtained by breaking the natural river boulders or quarry stones.

Fig. 17 – General fixing arrangement

Concrete stone masonry block –A precast cement concrete solid block having stone spalls in it (25 – 30 per cent of block volume) and cement concrete with dense stone aggregate and sand.  It is solid.

Fig. 18 – General arrangements of cramps

Stone face exposed block – A concrete stone masonry block where the stone spalls are exposed at one of its face.  The face, when forms the exposed wall face, the wall gets the texture of stone surface exposed.

5.3.1. Dimensions and tolerances - Concrete stone masonry block is a solid block and shall be referred to by its nominal dimensions.  The term ‘nominal’ means that the dimension includes the thickness of the mortar joint.  Actual dimensions shall be 10 mm short of the nominal dimensions.

The nominal dimensions of concrete stone masonry block shall be as follows:

Length             300 mm

Height             150 mm and

Width              100, 150 and 200 mm

In addition, block shall be manufactured in one third, half, two-thirds and three quarters of its full length. The nominal dimensions of the units are so designed that taking account of the thickness of mortar joints, they will produce wall lengths and heights which will conform to the principles of modular coordination. Blocks of other nominal dimensions may also be made if so directed by the engineer.

5.3.2. For accommodating vertical, reinforcement required in earthquake resistant construction, special block or half width and with semi-circular recess in it (see Fig. below) shall be used.  These dimensions are suitable for 200 mm thick wall.  Similar blocks shall be made for walls of thickness greater than 200 mm.

5.3.3. The maximum variation in the length of the units shall not be more than ± 5 mm and maximum variation in height and width of units more than ± 3 mm.

5.3.4. Subject to the tolerances as specified, the faces of blocks shall be flat and rectangular, opposite faces shall be parallel, and all arises shall be square.  The bedding surfaces shall be at right angles to the faces of the blocks.

5.3.5. Blocks with special faces - Blocks with special faces shall be manufactured and supplied as specified in the item or agreement.

5.3.6. Classification - Concrete stone masonry blocks shall be classified according to their average compressive strength as given in Table 2.

5.3.7. Materials

5.3.7.1. Cement - Cement should comply with specifications explained under Section-0 of KBS.

5.3.7.2. When cement conforming to IS: 269-1981 is used, replacement of cement by flyash conforming to IS: 3812-1981 may be permitted up to a limit of 20%.  However, it shall be ensured that blending of flyash maximum uniformity.

5.3.7.3. Stone Spalls - The stone spalls shall be of size ranging from 50 to 250 mm in dimension. The stone spalls shall be hard, sound, round in shape, durable, free from decay and weathering.  These shall not be flaky.  The spalls shall have rough surface for better bond with cement concrete.  Good quality stones, such as granite, sand stone and basalt shall be used.  Slate shale or any other soft and flaky stone shall not be used.  The spalls shall be obtained from approved quarry or by breaking river boulder.  Large size shall be broken into the required sizes and shall be stacked in to two categories:  (a) 100 mm and above, and (b) Below 100 mm.

5.3.7.4. Aggregates - The aggregates used in the manufacture of block shall be clean and free from all deleterious matter and shall conform to the requirements of IS: 383.

Maximum size of the coarse aggregates shall be 10 mm.  Sand used in the manufacture of blocks shall be well graded, clean and free from deleterious matter, and shall conform to the requirements of IS:383.  Besides it shall have fine particles 15 to 20% passing 300 micron I. S. Sieve and 5 to 15% passing 150 micron I. S. Sieve.

It is recommended that the fineness modulus of the combined aggregate shall be between 3.6 and 4.

5.3.7.5. Fly ash conforming to IS: 3812-1981 may be used for part replacement of fine aggregate up to a limit of 20%.

5.3.8. Manufacture - Blocks may be manufactured either at construction site or in factory on a central casting platform using steel moulds with or without surface vibration for compaction of cement concrete.

5.3.8.1. Mould - Moulds shall be fabricated using mild steel plates and mild steel angles for stiffening the plates. The mould shall be either fixed type (box with four side walls fixed at corners, and top and bottom open) or split type. Split type may be either individual or gang mould.  Where the compaction of the concrete is done manually, the mould may be either fixed type or split type.  When the compaction of the blocks is done with surface vibrator, the mould shall be only split type (individual or gang mould).

5.3.9.1. Mix - The cement concrete mix for concrete stone masonry blocks shall not be richer than one part by volume of cement to 9 parts by volume of combined fine and coarse aggregates, and shall not be leaner than one part by volume of cement to 13 parts by volume of combined fine and coarse aggregates.

5.3.9.2. In case of blocks where compaction is done manually, concrete mix of medium consistency (10-12 mm slump) shall be used in order to enable proper compaction and demoulding. The consistency of the mix should be such that it may cohere when compressed in the hand without free water being visible.

5.3.9.3. In case of blocks where compaction is done by external vibrator, concrete mix of very low consistency (zero slumps) shall be used in order to vibrate and compact the concrete under pressure.

5.3.9.4. Mixing - Concrete shall normally be mixed in a mechanical mixer unless otherwise permitted by engineer.  In case of hand mixing 10% extra cement shall be used without any extra payment in exceptional cases with the prior permission of engineer. Mixing shall be continued until there is a uniform distribution of the materials, and the mass is uniform in colour and consistency.

5.3.10. Placing and compaction - Depending upon the size of the stone spalls, these shall be used either in one layer or in two layers.  When used in two layers, large size spalls of 100 mm and above shall be placed in the bottom and concrete poured all around and at top, and shall be tamped manually.  Second layer of stone spalls of size 50 mm and above shall be placed over the first layer, and again concrete is poured all around and up to 20 to 30 mm above the top level of mould.

5.3.10.1. Depending upon the size of block the average volume of stone spalls used should generally be between 25 to 30%.  However, in no block, it shall be less than 20% of the volume of block.

5.3.10.2. Each stone Spall shall have a minimum space of about 15 to 20 mm around it.  For blocks with exposed stone texture, the stone spalls shall touch the surface of the mould.

5.3.10.3. Blocks may be compacted manually as well as mechanically.  In case of manual compaction, the concrete laid after the first layer of stone spalls shall be tamped with mason’s tool and again it shall be tamped with suitable tampers and compacted from top and finally struck off level with trowel. In case of mechanical compaction, the mould shall be filled up to overflow, vibrated and mechanically tamped using external vibrator and struck off level with trowel.

5.3.10.4. Demoulding shall be done 5 to 10 minutes after compaction.  In case of fixed type mould it shall be pulled up with side handles while pressing down the block with the plate at top with thumb.  In case of split type mould, the sides shall be removed first and the partition plates (gang mould) shall be pulled up subsequently.

5.3.10.5. After demoulding, the blocks shall be protected until they are sufficiently hardened to permit handling without damage.

5.3.11. Curing - The blocks hardened shall then be cured in a curing water tank or in a curing yard and shall be kept continuously moist for at least 14 days.

5.3.11.1. Drying - After curing, the blocks shall be dried for a period of two or four weeks depending upon weather before being used on the work.  The blocks shall be allowed to complete their initial shrinkage before they are laid in a wall.

5.3.12. Physical Requirements:

5.3.12.1. General - All blocks shall be sound and free from cracks or other defects which may interfere with the proper placing of the unit or impair the strength or performance of the construction.

5.3.12.2. Where blocks are to be used in exposed wall construction, the face or faces that are to be exposed shall be free of chips, cracks or other imperfections, except that not more than 5% of a consignment contains slight cracks or small chipping.

5.3.12.3. Dimensions - The overall dimensions of the blocks when measured as given in Appendix -A of IS: 12440 shall be in accordance with subject to the tolerance mentioned therein.

5.3.12.4. Compressive strength  - The minimum compressive strength at 28 days, being the average of eight blocks, and the minimum compressive strength at 28 days of individual blocks, when tested in the manner described in Appendix B, of IS : 12440, shall be as prescribed in Table 4.

Table 4 Compressive strength of concrete stone masonry blocks

Class designation

Minimum average compressive strength on blocks N/mm2

Minimum strength of individual blocks N/mm2

5

5.0

3.5

6

6.0

4.2

7

7.0

5.0

9

9.0

6.3

12

10.0

7.5

For 100 mm wide blocks (for 100 mm thick walls), the minimum strength may be 3.5 N/mm2.

5.3.12.5. Water absorption - The water absorption being the average of three blocks, when determined in the manner prescribed in Appendix C, of IS: 12440-1988 shall be not more than 6% by mass.

5.3.13. Tests

5.3.13.1. Tests as described in Appendix A of IS: 12440-1988 shall be conducted on samples of blocks selected according to the sampling procedure given to ensure conformity with the physical requirements laid down.

5.3.13.2. A sample of 15 blocks shall be taken from a lot of 5000 or part there of manufactured under similar conditions, of the same size and batch.

5.3.14. Criteria for conformity - The lot shall be considered as conforming to the requirements of the specification if the conditions in 5.3.14.2 and 5.3.14.3 are satisfied.

5.3.14.2. The number of blocks with dimensions outside the tolerance limit and /or with visual defects, among those inspected shall be not more than two.

5.3.14.3. For compressive strength, the mean value determined shall be greater than or equal to the minimum limit as specified in 5.3.12.4

5.3.14.4. For water absorption the mean value determined shall be equal to or less than maximum limit as specified in 5.3.12.5

5.3.15. Laying - The laying of precast concrete stone block masonry shall be as specified in 5.4.6

5.4. Specifications for Hollow and Solid Concrete Block Masonry

5.4.1. Hollow and solid concrete blocks – Shall conform to the requirements of IS: 2185. Specification for hollow and solid concrete blocks except with regard to the mix of cement concrete and sizes of aggregates which shall be as indicated.  Hollow blocks shall be sound, free from cracks, broken edges, honey combing and other defects that would interfere with the proper placing of block or impair the strength or performance of construction.

5.4.2. Dimensions and tolerances:

Concrete masonry building units shall be made in sizes and shapes to fit different construction needs.  They include stretcher, corner, double corner or pier, jamb, header, bull nose, and partition block, and concrete floor units. Concrete block-hollow (open or closed cavity) or solid shall be referred to by its nominal dimensions. The nominal dimensions of concrete block shall be, as follows:

Length             :           400, 500 or 600 mm

Height             :           200 or 100 mm

Width              :           50, 75, 100, 150, 200, 250 or 300 mm.

In addition, block shall be manufactured in half lengths of 200, 250 and 300 mm to correspond to the full lengths.

The maximum variation in the length of the units shall be not more than +/- 5 mm and maximum variation in height and width of unit, not more than +/- 3mm.

5.4.3. Classification:

5.4.3.1. Hollow (open and closed cavity) concrete blocks.

The hollow (open and closed cavity) concrete blocks shall conform to the following three grades:

  1. Grade ‘A’ - These are used as load bearing units and shall have a minimum block-density of 1500 kg / m3.  These shall be manufactured for minimum average compressive strengths of 3.5, 4.5, 5.5 and 7.0 N/mm2 respectively at 28 days (See Table 5).
  2. Grade ‘B’ -  These are also used as load bearing units and shall have a block density less than 1500 kg / m3 but not less than 1000 kg / m3.  These shall be manufactured for minimum average compressive strengths of 2.0, 3.0 and 5.0 N/mm2 respectively at 28 days. (See Table 5).
  3. Grade ‘C’ – These are used as non-load bearing units and shall have a block density less than 1500 kg / m3 but not less than 1000 kg / m3.  These shall be manufactured for minimum average compressive strength of 1.5 N/mm2 at 28 days (see Table 5).
  4. Grade ‘D’ – The solid concrete blocks are used as load bearing units and shall have a block density not less than 1800 kg/m3.  These shall be manufactured for minimum average compressive strengths of 4.0 and 5.0 N / mm2 respectively (see Table 5).

5.4.4. Physical requirements:

5.4.4.1. Compressive strength – The average crushing strength of eight blocks, when determined in accordance with IS: 2185 shall not less than as specified in Table 3:

Table 5 Physical requirements

Type

Grade

Density of block Kg/mm3

Minimum Average compressive strength of units

Minimum strength of individual units

N/mm2

Hollow (open & closed cavity) load bearing unit

A (3.5)

Not less than 1500

3.5

2.8

 

A(4.5)

4.5

3.6

 

A(5.5)

Not less than

1500 but not

less than 1000

5.5

4.4

 

A(7.0)

7.0

5.6

 

B(2.0)

2.0

1.6

 

B(3.0)

3.0

2.4

 

B(5.0)

5.0

4.0

Hollow (open and closed cavity) non-load bearing units

C(1.5)

Less than 1500 but not less than 1000

1.5

1.2

Solid load

D(5.0)

Not less than 1800

5.0

4.0

Bearing Units

D(4.0)

4.0

3.2

5.4.4.2. Drying shrinkage – The drying shrinkage of the blocks (average of three blocks), when unrestrained, shall be determined in accordance with IS: 2185 and shall not be exceed 0.1 per cent.

5.4.4.3. Moisture movement – The moisture movement (average of three blocks), when determined as described in IS: 2185 shall not exceed 0.09 percent.

5.4.4.4. Water absorption – The water absorption (average of three blocks), when determined in the manner described in IS: 2185 shall be not more than 10 per cent by mass.

Face shells and webs shall increase in thickness from the bottom to the top of the unit. Depending upon the core moulds used, the face shells and webs shall be flared and tapered or straight tapered, the former providing a wider surface for mortar.  The thickness of the face shell and web shell is not less than the values given in Table 4.

Table 6 Minimum face shell and web thickness

Nominal block length and width

Face shell thickness

Thickness of web

Total web thickness per course in any 200 mm of walling

 

Min.

Min.

Min.

100 or less

25

25

25

Over 100 to 150

25

25

30

Over 150 to 200

30

25

30

Over 200

35

30

38

Subject to the tolerance as specified in 5.4.2.2 and 5.4.4.7, the face of masonry units shall be flat and rectangular, opposite face shall be parallel, and all arises shall be square.  The bedding surfaces shall be at right angles to the faces of the blocks.

Blocks with special faces shall be manufactured and supplied as directed by the engineer.

5.4.5. Curing and drying - The blocks shall be cured in an immersion tank or in a curing yard and shall be kept continuously moist for at least 14 days.  When the blocks are cured in an immersion tank, the water of tank shall be changed at least every four days.

After curing, the blocks shall be dried in shade before being used on the work.  They shall be stacked with voids horizontal to facilitate through passage of air.  The blocks shall be allowed to complete their initial shrinkage before they are laid in wall.

5.4.6. Construction of masonry - For single storeyed buildings, the hollows of blocks in foundation and basement masonry shall be filled up with sand and only the top foundation course shall be of solid blocks.  But for two or more storeyed buildings, solid concrete blocks shall be used in foundation courses, plinth, and basement walls, unless otherwise indicated.  If hollow blocks are used, their hollows shall be filled up with cement concrete 1:3:6 using 12.5 mm nominal size aggregates.

5.4.7. Wetting of blocks - Blocks need not be wetted before or during laying in the walls.  In case the climate conditions so require, the top and the sides of the blocks may only be slightly moistened so as to prevent absorption of water from the mortar and ensure the development of the required bond with the mortar.

5.4.8. Laying - Blocks shall be laid in mortar, as indicated and thoroughly bedded in mortar, spread over the entire top surface of the previous course of blocks to a uniform layer of not less than 10 mm and not more than 12 mm in thickness.

All courses shall be laid truly horizontal and all vertical joints made truly vertical.  Blocks shall break joints with those above and below for not less than quarter of their length.  Precast half length closers (and not cut from full size blocks) shall be used.  For battered faces, bedding shall be at right angles to the face unless otherwise directed.  Care shall be taken during construction to see that edges of blocks are not damaged.

5.4.9. Provisions for door and window frames - A course of solid concrete block masonry shall be provided under door and window openings (or a 10 cm thick precast concrete sill block under windows).  The solid course shall extend for at least 20 cm beyond the opening on either side.  For jambs of very large doors and windows either solid unit are used, or the hollows shall be filled in with concrete of mix 1:3:6 using 12.5 mm nominal size aggregates.

5.4.10. Provisions for roof - The course immediately below the roof slab shall be built with solid blocks.  The top of the roof course shall be built with solid blocks.  The top of the roof course shall be finished smooth with a layer of cement and coarse sand mortar 1:3, 10 mm thick and covered with a thick coat of white wash or crude oil, to ensure free movement of slab.

5.4.11. Intersecting walls - When two wall meet or intersect and the course are to be laid up at the same time, a true masonry bond between at least 50% of the units at the intersection is necessary. When such intersecting walls are laid up separately, pockets with 20 mm maximum vertical spacing shall be left in the first wall laid.  The corresponding course of the second wall shall be built into these pockets.

5.4.12. Piers - The top course of block in the pier shall be built in solid blocks.  Hollow concrete block shall not be used for isolated piers, unless their hollows are specified to be filled with cement concrete.

5.4.13. Fixtures, fittings, etc. shall be built into the masonry in cement and coarse sand mortar 1:3 while laying the blocks where possible.  Hold fasts shall be built into the joints of the masonry during laying. Holes, chases, sleeves, openings, etc. of the required size and shape shall be formed in the masonry with special blocks while laying, for fixing pipes, service lines, passage of water etc.  After service lines, pipes etc. are fixed, voids left, if any, shall be filled up with cement concrete 1:3:6 (1 cement : 3 coarse sand: 6 stone aggregate 20 mm nominal size) and neatly finished.

5.4.14. Finishes - Rendering shall not be done to the walls when walls are wet.  Joints for plastering or pointing as specified shall be raked to a depth of 12 mm.  Joints on internal faces, unless otherwise indicated, shall be raked for plastering.  If the internal faces of masonry are not be plastered the joints shall be finished flush as the work proceeds or pointed flush where so indicated.

Annexure 5-A.1

BLOCK   WORK- CONSTRUCTION PRACTICE

1. General

1.1. Introduction

Blocks are either hollow or solid.  Generally they are of light weight compared to bricks. Concrete blocks to IS: 2185 (Part 1)-1979 may be used for both load bearing and non-load bearing walls.  The wall thickness will vary.

For high thermal insulation, cavity walls having inner leaf of light weight concrete blocks to IS: 2185 (Part 2)-1983 may be used.  Each leaf of cavity shall not be less than 100 mm.

Autoclave cellular concrete blocks to IS: 2185 (Part 3)-1984 shall not be used for foundations and for masonry below damp-proof course.

2. Mortars

2.1. Hollow concrete blocks:

Hollow concrete blocks shall be embedded with a mortar which is relatively weaker than the mix used for making blocks in order to avoid formation of cracks.  A rich or strong mortar tends to make a wall too rigid thus localizing the effects of movements due to temperature and moisture variations, resulting in cracking of blocks.  The recommended proportion of mortar measured by volume is given in Table 1

Table 7 Mix Proportion of mortar for hollow concrete blocks

Sl No

Masonry

Type of work

Normal masonry

(Cement: Lime: Sand)

Reinforced

(Cement: Sand)

1.

Normal work

1 : 1 : 9 to 10

1 : 7 to 8

2.

Exposed to severe conditions; high intensity of loads; plasters; heavily loaded lintels and beams.

1 : 1 : 6 to 7

1 : 4 to 5

3.

Partitions of 10 cm

1 : 1 : 7 to 8

1 : 5 to 6

Note: All mortars shall have a slump of 75 mm.

2.2. Light weight blocks - Light weight blocks shall be embedded with a mortar mix, the strength of which is lower than mix for making blocks, to avoid formation of cracks.  A 1:2:9 cement, lime, sand mortar may generally be used; for high intensity of load it shall be 1:1:6.  Autoclaved blocks shall be embedded in mortar as specified in Table 1

3. Concrete

3.1. Concrete used for filling hollow concrete block masonry when reinforced shall be 1 cement, 2 ½ sand and 3 coarse aggregate of size ranging from 4.75 mm to 10 mm.  The water cement ratio shall not exceed 0.6.  When cells exceed, 100 mm on the narrower side, the proportion of mix shall be 1of cement, 2 ½ of sand and 3 ½ of coarse aggregate for reinforced concrete and 1:3:6 plain concrete.

4. Thickness

4.1. For load bearing masonry built with hollow concrete blocks, the thickness of walls shall not be less than the values as obtained from IS: 1905-1987.

4.2. Light weight block in load bearing masonry for external walls in framed construction shall not be less than 200 mm.  However, if they are suitably braced by lateral or vertical supports, the thickness can be 100 mm.  Non-load bearing hollow block walls shall be not less than 100 mm.

4.3. Autoclaved block walls in framed construction shall also be as per above; except that for load bearing work, the minimum thickness shall be 200 mm; however it can be reduced to 150 mm if properly braced.

5. Lateral supports

Walls made of blocks shall have vertical or horizontal lateral supports at right angles to the face of the wall. Cross walls, plasters or buttress walls shall provide the lateral support.

6. Avoidance of crack formation

6.1. General

The major cracks in the walls or partitions in a structure constructed with blocks, whether they are of hollow of cellular types can be prevented.  The preventive measures to be undertaken are covered.

6.1.1. Structural movements

Cracks may arise from alterations in length, the curvature or orientation due to load settlement, thermal expansion or changes in moisture content.

In the case of framed structures, erection of partitions and panel walls shall be delayed wherever possible until the frame has taken up, as much as possible, any deformation occurring due to structural movements.

  1. Floor deformation and movement – The floor upon which a partition is built may deflect under load brought on it after the partition is built.  Such deflections tend to create a non-continuous bearing for the block leading to cracks in the partition.  This can be avoided by embedding wires of 3 mm diameter of mild steel or galvanized steel or welded wire mesh strip in bed joints in cement mortar 1:2 after every 900 mm to 1200 mm height.
  2. Ceiling deflection and movement – A ceiling above a partition will may deflect under loads applied after its erection or through thermal or other movements.  To avoid cracking as a result of such deflection, the partition wall shall be separated from the ceiling by a gap or by a layer of resilient material or lean mortar.  When this cannot be done as in the case of plastered finishes, the risk of cracking may be reduced by forming a cut between the ceiling plaster and the wall plaster.
  3. Deflection or movement of structural abutments – The walls, columns or other structural elements against which the wall or partition abut, may deflect or move because of load, settlement, shrinkage or thermal effects.  In order to avoid cracking of walls or partitions as a result of such movements, a slip joint shall be provided where possible, preferably packed with a resilient mortar or lean mortar.
  4. Cracks in partition walls may occur at corners of door and window frames at lintel level or sill level.  It may therefore be desirable to provide a nominal reinforced concrete band beam (see Fig. 1) at sill level and vertical reinforced concrete stud at either side of vertical members of frames which may in addition provide sufficient anchorage for hold fast.

6.1.2. Control of wall movements accompanying temperature and moisture changes Cracking in concrete masonry walls is often due to tensile stresses which develop when wall movements accompanying temperature and moisture change are restrained by other elements of the building or when concrete masonry places restraint on the movement of adjoining elements.

There are three methods of controlling cracking in concrete masonry structures :

(1). Specifying a limit on the moisture content of masonry units at the time of delivery and   construction; 

(2) Incorporating steel reinforcement either in the form of nominal bond beams or horizontal joint reinforcement and, 

(3) Providing control joints to accommodate the movement of masonry. In all concrete masonry construction, it is essential to employ only moisture controlled units.  Their use, combined with the provision of control joints is generally adequate to prevent cracking in concrete masonry walls. However, bond beams or joint reinforcement, or both in different locations as considered suitable may also be used in addition to the above.

6.1.3. Nominal bond beams - Bond beams, the use of which as structural members have been referred shall also serve as a means to crack control.  Normal bond beams shall be built in the same manner as the structural bond beams with a minimum reinforcement of two 8 mm mild steel bars or two 6 mm dia high strength deformed bars.  Their value for this purpose is due to increased strength and stiffness they provide to a masonry wall. As a means of crack control, the area of influence of bond beam shall generally be assumed to be extending 600 mm above and below its location in the wall.  In walls without openings, they shall be placed at 1200 mm apart and may be of any length up to a maximum of 18 m (see Table 2).See Fig. 1.

Nominal bond beams shall be discontinuous at control joints, but practice here varies depending on the structural requirements.  Dummy joints shall be formed when a bond beam is continuous at a control joint.

6.1.4. Joint reinforcement - Horizontal joint reinforcement serves much the same purpose as bond beams in crack control.  It increases stresses to cracking.  Due to closer spacing adopted, joint reinforcement may be more effective in crack control than bond beams.

  1. Joint reinforcement shall be preferably be fabricated from galvanized steel to IS 280:1978 and shall consist of two or more smooth or deformed longitudinal wires 3 mm dia or larger weld connected with 2.8 mm dia or larger cross wires.  The out-to-out spacing of longitudinal wires shall be 30 mm less than the width of masonry skills.  Cross wires shall be welded at a pacing of 150 mm for smooth wires and 400 mm for deformed wires.  Where splice in wires is necessary, it shall be lapped to a length of at least 300 mm.
  2. The reinforcement shall be embedded in horizontal joints at intervals of 900 mm to 1200 mm depending on panel length, height and the number and type of wall openings.  (See Table -2)
  3. Joint reinforcement shall be used in conjunction with cement mortar not weaker than 1:2 mixes.  In walls exposed to action of weather, the reinforcement shall have a mortar cover of not less than 15 mm.
  4. Notwithstanding the above, location of joint reinforcement shall be as follows :
  1. Place the joint reinforcement in the first and second bed joints immediately above and below wall openings ;
  2. It shall not extend less than 600 mm beyond the openings to end of the panel whichever is smaller ;
  3. Place joint reinforcement within two or three courses immediately below the top of the wall ;
  4. Joint reinforcement shall not be located closer to a bond beam than 600 mm ; and
  5. Joint reinforcement shall be interrupted at control joints.

Notes: (1) When bond beams spaced at 1200 mm are used in place of joint reinforcement, control joints shall be spaced at 18 m. (2) Where reinforcement has not been provided, the ratio L / H of wall panel shall conform to IS: 1905-(1987)

Fig. 1 Nominal reinforced concrete bond beam at sill level

Table 2: Recommended length top height ratios for concrete block masonry

Sl 

No

Wall panel

Vertical spacing of joint reinforcement

900 mm

1000 mm

1200 mm

1

Length of panel (L) Irrespective of height (H) Max.

18 m

15 m

12 m

2

Ratio L/H, Max

 

 

 

a)

200 mm thick wall

3.0

2.75

2.50

b)

300 mm thick wall

2.25

2.00

1.75

6.1.5. Control joints - Control joints are employed to reduce restraint by accommodating movement of masonry wall or movement of structural elements adjacent to the wall, and thus to control cracking.  They are in fact vertical separations built into the wall at locations where cracking is likely due to excessive horizontal stresses.  The spacing along the wall length depends upon:

(a) Expected movements of the wall and other elements

(b). Resistance of the wall to horizontal stresses

(c) The extent and location in the wall of doors, windows, recesses, chases and other causes of stress concentration. Some typical methods of control joints are shown in Fig 2 and Fig. 3.

6.2. Bonded beams and studs used on structural members

6.2.1. Reinforced concrete structural bond beams may be used in concrete block masonry to meet the requirements of unusual stress conditions.  Examples are as below:

  1. In buildings in earth-quake regions ;
  2. In buildings in areas where severe  wind storms occur ;
  3. In buildings in areas where unfavorable soil movements and soil subsidence occur ; and
  4. In buildings where walls are subjected to excessive vibration or to heavy loads.

In all such cases, it is necessary to provide more than nominal stability for all types of masonry walls.

6.2.2. Bond beams shall be built integrally with block masonry or with special U-shaped lintel blocks slung together with reinforcing steel placed in the core of hollow of blocks filled with M15 concrete. The reinforcement shall conform to IS: 456-2000; but in no case shall be less than two

12 mm dia mild steel bars. The beams are discontinuous at control joints; but the joints should be designed to transfer forces along the wall.

6.2.3. Bond beams may be provided at any of the following locations depending on the conditions as described in 6.2.1

(a) At floor level; (b) At top of all door and window openings (in which case they serve as lintels over them); (c) Below the sill in all window openings and (d) At plinth level.

6.2.4. Apart from the horizontal bond beams, vertical reinforced concrete studs may also be provided at corners, at wall openings and at regular intervals between wall openings.  The studs shall be tied in with bond beams.

Non-structural use of bond beams is already covered 6.1.3

7. Preparatory works

Wetting of blocks

7.1. The blocks need not be wetted before or during the laying of the blocks.  In case the climatic conditions so require, the top and sides of the blocks may be slightly moisture so as to prevent absorption of water from the mortar and ensure development of the required bond with the mortar.

7.2. Scaffolding - Scaffolding shall be on the same lines as brickwork, suitably modified where necessary.

8. Laying of Concrete Blocks

8.1. First Course - The first course of concrete block shall be laid with great care, making sure that it is properly leveled, aligned and plumbed, to assist in obtaining a straight and truly vertical  wall. Before laying the first course, the alignment of the wall shall be marked on the d. p.c. The blocks for this course shall be laid dry, that is, without mortar along a string stretched between properly located corners of the wall in order to determine the correct position of blocks including those of the cross walls jointing it and also adjust their spacing. When the blocks are in proper position, the two corner blocks shall be removed, a mortar bed spread and these blocks re-laid back in place truly level and plumb.  The string shall then be stretched tightly along the faces of two corner blocks and the faces of the intermediate blocks adjusted to coincide with the line.  Thereafter each block shall be removed and re-laid over a bed of mortar.  After every three or four blocks are laid the correct alignment and vertically be checked.

8.2. Construction - The construction of walls may be started either at the corners first or started from one end proceeding to the other end.

If the corners are built first, they shall be built four or five courses higher than the centre of the wall.  As each course is laid at the centre, it shall be checked for alignment and level and for being plumb. Each block shall be carefully checked for alignment with a straight –edge to make sure that the faces of the blocks are in the same plane.

Fig. 2 – Control joints in concrete block masonry construction

8.2.1. Each course, in building the corners, shall be stepped back by a half-trick and the horizontal spacing of block shall be checked by placing a mason’s level diagonally across the corners of the blocks. A storey rod or course pole, suitably marked provides an accurate method of finding the top of the masonry for each course.

8.2.2. When filling in the wall between corners, a mason’s line shall be stretched from corner to corner for each course and the top outside edge shall be laid true to this line.  The manner of handling or gripping the block shall be such as to position the block properly with minimum adjustment.

8.2.3. To ensure satisfactory bond, mortal shall not be spread too far ahead of actual laying of the block as it will stiffen and lose its plasticity.  As each block is laid, excess mortar extruding from the

Joints shall be cut off with a trowel and thrown back on the mortar board to be reworked into fresh mortar. If the work is proceeding rapidly, the extruded mortar cut from the joints may be applied to vertical face shells of the blocks just laid.  If there be any delay long enough for the mortar to stiffen on the block, the mortar shall be removed to the mortar board and reworked.  Dead mortar that has been picked up from the scaffold or from the floor shall not be used.

Fig. 3

8.3. Closure block - When installing a closure block, all edges of the openings and all four edges of the closure block shall be buttered with mortar.

The closure block shall be carefully lowered into place.  If any mortar falls leaving an open joint, the closure block shall be removed, fresh mortar applied and the operation repeated.

9. Provision for door and window frames

9.1. Door and window frames shall be attached to the surrounding masonry either by conventional method or by 200 mm flooring nails with screwed ends fixed directly into the block, after the frame has been edged into the opening at every nailing position.  The number of nails depends on the dimensions of the frames.  The nails shall be spaced at a maximum of 400 mm apart and the first nail shall not be farther than 200 mm from the corner. 

Frames may be attached to the masonry by holdfasts anchored in the vertical reinforced concrete studs provided to the frames.

10. Provision for roof

10.1. The top of the roof course shall be finished smooth with a thin layer of 1:3 cement mortars and covered with a coat of crude oil or craft paper or oil paper to ensure free movement of the roof.

11. Intersecting wall

11.1. Load bearing walls - When two load bearing walls intersect and courses are to be laid up at the same time, a true masonry bond between 50 per cent of the units at the intersection is necessary.  When such walls are laid up separately, pockets with maximum 200 mm vertical spacing shall be left in the first wall laid.  The corresponding course of the second wall shall be built in to these pockets.

11.2. For non-load bearing walls same bonding methods as for load bearing walls may be used.

All finishes shall be as specified in Section 12 Finishing Work, as the case may be.

Fig. 3

Fig. 3 – Plasters with control joints in concrete block masonry construction

 

Annexure 5-A.2

CONSTRUCTION PRACTICES OF IN-SITU WALLS WITH SOIL CEMENT

1. General

1.1. This type of in-situ construction with soil cement shall be limited to single storey construction with a wall height not exceeding 3.2 mm and a minimum wall thickness of 300 mm for load bearing and 200 mm for non-load bearing walls.

1.2. The procedure described herein may also be followed for rammed in-situ wall construction with unstabilized soil, provided the surfaces of the wall are protected by a waterproof mud plaster.

2. Soil

2.1. Raw soil used for soil cement shall be free from deleterious contents, such as organic matter of vegetable origin, mica, etc.  Black cotton soil may not be used from economy considerations.

Soil shall conform to the following requirements:

Sand content, percent by mass                              35, min

Plasticity index, percent                                          8.5 to 10.5

Total soluble salts, percent by mass                       1, max

Sodium salts, percent by mass                                0.1, max

Liquid limit, percent                                                  27, max

Note: Sand content is the fraction of sand of the soil that passes 425 micron is retained on 75 microns IS sieve.  More than half the material is smaller than 75 micron by mass.

2.2. Soil shall be prepared as per IS 2110: 1980.  Cement shall be mixed in proportions as given below:-

(a)For construction of walls 2.5 to 3.5 per cent by mass of dry soil depending on the density to be obtained.  For construction of walls below plinth level and for copings. 5 to 7.5 per cent by mass of dry soil, so that the crushing strength of blocks mate shall not be less than 1.4 N/mm2 (14 kg/cm2) for dry condition.

For calculation purposes the unit weight of dry soil shall be taken as 1 300 kg/m3.  Properties of soil cement shall be as in IS 2110: 1980.

2.3. Preparatory work:

2.3.1. Shuttering - Any timber planks suitable in local practice may be used for shuttering.  The planks shall not be less than 200 mm in width and 50 mm in thickness. 

A typical arrangement is shown in Fig. 4

Fig. 4 – Typical details of shuttering for 300 mm thick wall

Note: If the thickness of the wall is greater than 300 mm, shuttering details will have to be suitably modified.  The shuttering shall generally be in lengths ranging from 1.8 m to 3.3 m.  The height of the shuttering for one lift shall be about 600 mm clear for casting the wall plus 200 mm for holding on to the portion of the compacted wall below in the previous lift. The shuttering may be lifted immediately after first lift is well compacted and the shuttering for next lift arranged.

3. Wall constructions

3.1. Preparation of soil - After the shuttering is erected, the moist stabilized soil shall be poured into the shuttering in layers of 75 mm at a time.  The layer shall be uniform in depth.  To control his depth, templates may be used.

3.2. Compaction - Compaction shall be done by iron rammers.  Compaction shall be started at the side and worked inwards.  Ramming of the sides shall be evenly distributed to avoid tilting of the shuttering.  Verticality of the shuttering shall be checked as compaction proceeds.

3.3. Curing - The walls shall be cured for 15 days after removal of shuttering.  Curing shall be done by slight sprinkling of water at regular intervals.

3.4. Joints - Vertical joints shall be provided at a spacing of not more than 2 m apart.  Vertical joint shall be staggered.  Fig. 5 gives details of joint.

Fig. 5 – Typical details of construction joints in in-situ of the soil, cement walls of 300 mm thickness

Horizontal joints shall be formed by finishing smooth the rammed surface at the end of each lift.

3.5. Fixing frames - Frames for door and windows shall be fixed by iron hold fasts inserted in the wall before-hand.

3.6. Bearing of roof - Where light roof frame work is to rest on the wall, the portion of the wall directly below it shall be built with bricks laid in cement mortar 1:6 for a depth of 150 mm; or bricks made out of 7.5 per cent soil cement.  Beams shall rest on cement concrete bed plates.  Trusses or flat roofs shall rest on brick bearing course to a depth of 150 mm laid in cement mortar 1:6.

3.7. Lintels - Reinforced brick or cement concrete lintels may be used.  The space above the lintels shall be filled either with soil cement rammed in-situ, or precast soil cement blocks laid in cement in mortar mix 1:6.

3.8. Parapet - The parapet shall be of brick work.  A drip course shall be provided to drain rain water from parapet and away from the lower portions of the walls on to the roof surface.  The plaster finish of the roof shall be continued from the roof surface right up to the drip course in the parapet.

3.9. Plastering - Cement plaster of mix hot leaner than 1:5 shall be used.  It shall be applied after drying the wall for four weeks at least.  The wall surface shall be given a neat cement wash before applying plaster.

4. Preparation of mud plaster:-

4.1. Add cutback bitumen to IS 217: 1988, grade 80/100 to mud with BHUSA which is allowed to rot for a week.  About 60 kg of 'Bhusa' should be added to a cubic meter of mud.  Bitumen should be around 40 kg/m3 of soil used.

4.2. Surfaces to be plastered shall be moistened before application of mud plaster.

 

Annexure 5-A.3

LIST OF BUREAU OF INDIAN STANDARDS  (IS)

IS: 737-1986

Wrought aluminium and aluminium alloy, steel and strip for general engineering purpose. (3rd Revision)

IS: 1121-(Part I) 1974

Methods of test for determination of properties and strengths of Natural building stones (Part I-compressive strength).             (1st Revision) (Amendment I)

IS: 1122-1974

Methods of test for determination of specific gravity of natural Building stones.  (1st Revision)

IS: 1123-1975

Methods of identification of natural building stones. (1st Revision)

IS: 1124-1974

Methods of test for determination of water absorption, apparent Specific gravity and porosity of natural building stones.  (1st Revision)

IS: 1125-1974

Methods of test for determination of weathering of natural building stones (1st Revision)

IS: 1126-1974

Methods of test for determination of durability of natural Building stones. (1st Revision) (Amendment I)

IS: 1128-1974

Lime stones (slab & tiles). (1st Revision)

IS: 1129-1972

Recommendations for dressing of natural building stones.  (1st Revision) Reaffirmed 1993

IS: 1200 (Part 4) -1976

Methods of measurements of building and Civil engineering works: Part 4 : Stone masonry. (3rd Revision) Reaffirmed 1992

IS: 1597 (Part 1)-1992

Code of practice for construction of rubble stone masonry : Part 1 : Rubble Stone masonry (1st Revision)

IS: 1597 (Part 2)-1992

Code of practice for construction of ashlar stone masonry : Part 2 : Ashlar masonry (1st Revision)

IS: 1805-1973

Glossary of terms relating to stones, quarrying and dressing. (1st Revision)                                 

IS: 2185-(Part1)-1979

Concrete masonry units: Part 1: Hollow and solid concrete blocks.  (2nd Revision) (Amendment 1) 2005

IS: 2572-1963

Code of practice for construction of hollow concrete blocks Masonry.  2005

IS: 3620-1979

Laterite stone block for masonry. (1st Revision) 1993

IS: 3622-1977

Sand stone (slab & tiles) (1st Revision)

IS: 4101-(Part 1)-1967

Code of practice for external facings and veneers: Part 1: Stone facing, Reaffirmed 1990

IS: 4101-(Part 2) 1967

Code of practice for external facings and veneers: Part 2: Cement concrete facing.   1990

IS: 12440-1988

Precast concrete stone masonry blocks.

IS: 269-1989

33 grade Ordinary Portland Cement. (4th Revision) (Amendments 3)

IS: 1489-1991

Part 1: Portland Pozzolana Cement: Part 1: Fly ash based (3rd Revision)

Part 2: Portland Pozzolana Cement: Part 2: Calcined Clay based.  (3rd Revision)    

IS: 6909-1990

Specification for Super sulphated Cement.  (Amendments 2)

IS: 8041-1990

Rapid hardening Portland cement.  (2nd Revision) (Amendments 2)

IS: 8043-1991

Hydrophobic Portland cement.  (2nd Revision) (Amendments 2)

IS: 3812-1981

Fly ash for as Pozzolana and admixture. (1st Revision) Part I & II 2003

IS: 383-1970

Coarse and fine aggregate from natural sources for concrete. (2nd Revision) Reaffirmed 1990

IS: 453-1993

Double acting spring hinges. (3rd Revision)

IS: 1122-1974

Method of test of determination of true specific gravity of natural building stones. (1st Revision) Reaffirmed 1993

IS: 1124-1974

Method of test for determination of water absorption, apparent Specific gravity and porosity of natural building stones.

(1st Revision) Reaffirmed 1990.

IS: 1130-1969

Marble (blocks, slabs and tiles).  Reaffirmed 1993

IS: 4101(Part-1) -1967

Code as practice for external facing and veneers: Part 1 Stone facing.  Reaffirmed 1990.

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