2-Stones

Civil Engineering Materials

Lecture 2 : STONES

University of Lahore, Islamabad Campus

STONES

What is a stone? It is a natural material of construction obtained from quarries.

Quarry is a place, typically a large, deep pit, from which stone or other materials are extracted.

Stone is also defined as natural, hard substance formed from minerals and earth material which are present in rocks.

Stone is a piece of rock. And rock is an aggregate of minerals.

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The term rock is commonly defined hard mass of mineral matter having, as a rule, no definite external form. In engineering construction the word stones applied indiscriminately to all classes of hard rocks.According to their geological origin, rocks may be classified as igneous, sedimentary, and metamorphic.Scientific classification of stones:• Siliceous Stones: Basic constitute in silica: Sandstone, Trap and

Granite.• Argillaceous Stones: Clay based. Laterite and Slate• Calcareous Stones: Where base is Carbonates of Lime. Lime stone

and Marble.Important building stones include: Granite, Gneiss, Trap, Limestone, Marble, Sandstones, Slate and Quartzite

Basic definitions and Types:

Some of the rock forming minerals are quartz, feldspar, mica, dolomite etc.

The conditions which govern the selection of stone for structural purposes are cost, ornamental value and durability.

A few examples of stone used are:Most of the forts world over

• Taj Mahal of India• Pyramids of Egypt• Great wall of China

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Civil Engineering UsesConstruction of residential and public buildings

Construction of dams, weirs, harbors, bridge abutments, etc.

Face work of structures for appearance and ornamental value

Road metal and railway ballast

Aggregate for concrete

Stone dust as substitute for sand

Thin slabs for roofing, flooring and pavements

Limestone for manufacture of lime, cement, etc.

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Foundation

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Stone Foundation Lintel04/22/23 02:21 7

Wall

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Bridge

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Weir is a low wall or dam built across a stream or river to raise the level of the water or to change the direction of its flow.

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Stone Weir

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A dam is a high wall of concrete that is erected across a river to impound water behind the wall and to increase the flow of water.

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Bridge Abutment

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Stone Abutment

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Harbor  is a body of water where ships and boats can seek shelter from stormy weather, or else are stored for future use.

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Stone has been extensively used in almost all the elements of building structures, as load carrying units as well as for enhancing the beauty and elegance of the structure.

Stone has gradually lost importance as a building material because of the following reasons:• With the advent of cement and steel.• Strength of the structural elements built with stones

cannot be rationally analyzed.• Difficulties in transportation A lot• And Dressing consume a lot of time of time is• resulting in slow pace of construction.

consumed

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Rock Forming Minerals

As Rock is an aggregate of minerals, so its properties are dependent upon the character of these constituents (minerals).

• These minerals are identified by their physical properties such as hardness, cleavage, streak, color, luster, specific gravity and shape of crystals.

• Some minerals feature great strength, hardness and resistance to chemical attack (quartz)

• Some have poor strength and readily soak in water (gypsum)• Some minerals display a great tendency to cleavage and split

readily along one or several directions (mica), thus decreasing the strength of the rock they make up.

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Properties of MineralsHardness is the most important property for rapid determination

of minerals. It is measured by scratching the mineral with a series of substances

of known variation in hardness using the following Mohs scale of hardness:Talc, easily scratched with the thumb-nail: 1Gypsum, scratched by the thumb-nail: 2Calcite, not scratched by thumb-nail but easily cut by knife: 3Fluorite, can be cut by knife with greater difficulty than calcite: 4Apatite, can be cut only with difficulty by knife: 5Orthoclase, can be cut with knife with great difficulty on thin edges: 6Quartz, not scratched by steel, scratches glass: 7Topaz: 8Sapphire: 9Diamond: 10Tall Girls Can Fight and Other Queer Things Can Do

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Properties of Minerals

Cleavage

It is the measure of the capability of some minerals to split along certain planes parallel to the crystal faces.

The various types of cleavage seen in the minerals are Basal, Prismatic, Cubic, Rhombohedral and Octahedral.

Streak

It is the color of the mineral in powder-form.For some minerals, their color is seen to be entirely different from that of their powder, which makes streak a useful property in the identification of ore-minerals.

Streak can be readily observed by scratching it on a streak plate made of unglazed porcelain or roughened glass.

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Properties of Minerals

Color

It is a valuable characteristic of metallic minerals, but less reliable for non-metallic minerals.

Luster

It is shine on the surface of a mineral and its appearance under reflected light.

It is classified as vitreous (glassy), greasy, pearly, resinous, dull, silky and metallic.

Crystal The crystal form is of importance when a mineral has had the opportunity to develop its natural shape. This is not the normal condition in rock structure.

Chemical Composition and Physical Properties of minerals.

See Table 3.1 Building Materials by S.K. Duggal (page 54) 04/22/23 02:21 21

Classification of Rocks

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Classification of Rocks

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Classification of Rocks

•Physical classification• Stratified rocks – separable distinct layers. Cleavage plane

of split visible. • Slate, sandstone, lime stone.

• Un-stratified rocks – no sign of strata, cannot be easily split into thin layers.

• Granite, basalt, trap.• Foliated rocks – having tendency to split up only in a

definite direction.• Most of metamorphic rocks have a foliated structure.• Except for quartzite and marble which have granulose

structure.

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Classification of Rocks

Geological classification

Igneous rocks (primary, un-stratified or eruptive rocks) They are of volcanic origin and are formed as a result of solidification of molten mass lying below or above the earth’s surface. The inner layers of the earth are at a very high temperature causing the masses of silicates to melt. This molten mass called magma is forced up as volcanic eruptions and spreads over the surface of earth where it solidifies.

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Igneous Rocks

The texture of the rock is greatly influenced by the rate of cooling of the magma.

When magma cools rapidly, its mass expands under the pressure of intensively evolving gases.

Subsequent rapid cooling of swollen lumps of magma gives rise to glassy porous rock known as pumice used as aggregate for light weight concrete.

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Fig. 6.02W. W. Norton

Igneous Rock Samples

Extrusive Lava Flow-McGraw Hill Pub. Intrusive Granite –www.windows.ucar.edu

GRANITE

Red Granite

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Classification of Igneous Rocks

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Geological classification

• Sedimentary Rocks are also known as aqueous or stratified rocks.• The various weathering agencies, e.g. rain, sun, air, frost, etc. break

up the surface of earth.• Rain water carries down these broken pieces to the rivers.• As the rivers descend down to the plains, the velocity decreases

gradually and the sediments (disintegrated rock pieces, sand, silt, clay, debris, etc.) in the water settle.

• Due to the seasonal variation, sedimentation takes place in layers. • With time, the sediments get consolidated in horizontal beds due to

the pressure exerted by overlying material.

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Sedimentary Rocks• The properties of the sedimentary rocks vary considerably depending upon

• Nature of the sediment• Type of bond between the sediment and grains.

• Usually, the rocks are well stratified and show well defined bedding planes.• The rocks are soft and can be easily split up along the bedding as well as

normal planes.• The examples of sedimentary rocks resulting from the precipitation of salts

in drying water basin (chemical deposits) are gypsum, anhydrite, magnesite, dolomite.

• Sedimentary rocks resulting from the accumulation of plant or animal remains (organogenous rocks) are limestone, shale, chalk.

• The examples of rocks resulting from the deterioration of massive magmatic or sedimentary rocks (fragmental rocks) are sandstone, sand, gravel.

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Sedimentary structures (Physical features)

1. Layers (bedding, or “strata”)

each layer is unique

deposited horizontally

separated by bedding planes

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conglomerate sandstone siltstone shale

claysiltsandgravel

sediments

sedimentaryrocks

Geological Classification

• Metamorphic Rocks are formed from igneous or sedimentary rocks as a result of the action of the earth movements, temperature changes, liquid pressures, etc.

• Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks.

•  There are two basic types of metamorphic rocks: 1) Foliated metamorphic rocks

have a layered or banded appearance that is produced by exposure to heat and directed pressure such as gneiss, phyllite, schist and slate2) Non-foliated metamorphic rocks

do not have a layered or banded appearance such as marble and quartzite 

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0 kmSedimentaryrock

Metamorphicrock

Igneousrock

50 km

10 km

~200ºC

~800ºC

Incr

easi

ng d

epth

and

tem

pera

ture

Melting

Metamorphism

Sedimentaryrock

Sediment

Metamorphism occurs between about 10 and 50 km of depth

These rocks don’t melt

Gneiss

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Pink Marble

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Rock Cycle

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Classification of Rocks

•Chemical Classification• Siliceous rocks – principal constituent is silica SiO2

(sand). • Granite, basalt, trap, quartzite, gneiss, syenite, etc.

• Argillaceous rocks – principal constituent is clay or alumina Al2O3.

• Slate, laterite, etc.• Calcareous rocks – principal constituent is calcium

carbonate or lime. • Limestone, marble, dolomite, etc.

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Characteristics of GoodBuilding Stones• Appearance & color – uniform color, lighter shades

preferred, free from clay holes, bands or spots • Structure – Not dull in appearance, crystalline homogenous

close grained is good, stratification should not be visible• Weight – heavier are compact, less porous, good for

hydraulic structures such as dams etc. Light stones may be the choice for arches, domes etc.

• Strength – generally compressive strength needed, igneous rock stones are stronger

• Hardness– resistance to abrasion, friction and wear. Hardness scale 1 to 10

• Toughness – Withstand impact, vibrations, moving loads

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Characteristics of GoodBuilding Stones• Porosity and Absorption – exposed surface absorbs rain

water forming acids causing crumbling action. Cyclic freezing and thawing of pore water

• Seasoning – hardening and weathering affect due to evaporation of quarry sap and formation of crystalline film. 6 to 12 months for proper seasoning

• Weathering – resistance to action of weather• Resistance to fire – free from calcium carbonate or oxides of

iron and minerals having different coefficients of expansion.• Durability – compact, homogenous and less absorptive is

more durable• Cost – quarrying, transportation, dressing and installation

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Evaluation of Stones

Tests of Stones

• Weathering test of natural building stones• Durability test of natural building stones• Water absorption and porosity test• Test for determination of true specific gravity• Compressive strength test

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Selection of Sample for Tests

• A truly representative sample of grade of stone should be selected

• Sample may be selected from quarried stone or natural rock

• Test pieces shall be free from seams or fractures

• In case of field stones and boulders separate samples shall be selected of all classes of stones based on visual inspection

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Weathering Test

• Specimen• 5 cm diameter, 5 cm high cylinders/5 cm cubes• Smooth finished, edges rounded to 0.3 cm

1.Three test specimens oven dried at 105 ± 5°C for 24 hrs. and cooled in desiccators down to room temp 20 to 30°C

• W1 will be weight of cooled and dried test piece, weighed to nearest 0.01 gm

2. Specimens submerged in water for 24 hrs at room temp• W2 immersed and freely suspended sample weight3. Remove the specimen from water, wipe off surface water

and wait about 3 to 5 minutes.• W3 will be weight after removal from water

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Weathering Test

4. Place the specimen in a glass dish in solution of 25 ml of water and 2 gm of powdered gypsum

• Specimen dish kept in oven at 105 ± 5°C for 5 hrs till gypsum powder becomes dry

• Specimen cooled down to room temp 25 ± 5°C• Heating and cooling cycle is repeated 30 times• Specimen removed and cleaned with wire brush• W4 weight of sample in air after 30 cycles5. Again immersed in water and W5 be weight of

sample.

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Weathering Test

• A1: Original absorption of specimen on 24 hr immersion in water• A2: Final absorption after 30 cycles• V1: Original volume after 24 hrs immersion in water• V2: final volume after 30 cycles• d: density of water at observation temperature( Given )

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100)()(

%

100%

100100

23

2354

542

231

1

3412

1

142

1

131

WW

WWWWVolumeinIncrease

d

WWVand

d

WWV

W

WWAAAbsorptioninIncrease

W

WWAand

W

WWA

Durability Test

• Specimen• 5 cm diameter, 5 cm high cylinders or 5 cm cubes• Smooth finished, edges rounded to 0.3 cm

1. At least three test samples dried for 24 hrs and weighed as W1

2. Samples suspended in solution of 14% sodium sulphate decahydrate (Na2SO4·10H2O)(density 1.055 kg/m3) for 18 hrs at room temperature

• Samples air dried for 30 minutes• Samples now oven dried for 24 hrs at 105 ± 5°C

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Durability Test

• Samples cooled down to room temperature to complete one cycle

• Weight W2 at the end of every 5th cycle noted and 30 cycles completed

• Durability expressed as

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1001

21

W

WWWeightinChange

Water Absorption and Porosity Test• A cube weighing 50 gm from given sample is prepared and its actual weight W1 is recorded.

• The cube is then immersed in distilled water for 24 hrs.

• It is taken out of water and its surface wiped with a damp piece of cloth. The cube is then weighed be it w2.

• The cube is suspended freely in water and its weight is recorded, let it be w3.

• The cube is then kept in boiling water for five hrs.• It is then removed and its surface water is again wiped

off with a damp piece of cloth, and its weight be w4.

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Water Absorption and Porosity Test• % absorption by weight after 24 hrs= w2-w1/w1 *100

• % absorption by volume after 24 hrs= w2-w1/w2-w3 *100

• % porosity by volume= w4-w1/w2-w3*100

• Saturation Coefficient= water absorption / total porosity = w2-w1/w4-w1

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True Specific Gravity Test

• Crush 0.5 kg of thoroughly washed specimen to 3 mm size, mix and make samples of 50 gm each

• Sample is ground in agate mortar to pass 150 microns sieve• Sample is dried at 100°C, cooled in desiccators• Specific gravity bottle is cleaned, washed, dried, cooled and

weighed (W1)• About 15 gms sample placed in specific gravity bottle closed

with stopper and whole weighed as W2

• Three fourths of specific gravity bottle filled with distilled water

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True Specific Gravity Test

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• Bottle boiled for 10 minutes while removing entrapped air• Bottle cooled to room temperature, filled with water,

stoppered and weighed as W3

• Bottle emptied, washed, filled with only distilled water, stoppered and weighed at room temperature as W4

GravitySpecificTrue

GravitySpecificApparantGravitySpecificTruePorosityTrue

WWWW

WWGravitySpecificTrue

)()( 2324

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Kind of StoneSpecific WeightPounds perCubic Foot

Specific GravityWater AbsorbedPounds perCubic Foot

Granite..Sandstone..Limestone...Marble......Trap........

165145155165175

2.72.32.52.72.8

.63.67.01.0.7

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Test for Compressive Strength

• Specimen Preparation• Cube size 40 mm, cylinder diameter 40 mm, height 40 mm• Load bearing surfaces finished as nearly true, parallel and

perpendicular planes as possible/otherwise apply plaster of Paris• Specimens kept immersed in water at 20 to 30°C for 72 hrs for

saturated condition testing• Specimens oven dried at 105 ± 5°C for 24 hrs and cooled down to

room temp for dry testing

• Testing load gradually increased @ 13.7 N/mm2 per minute until break down

• Max load applied divided by area of bearing surface is taken as the compressive strength of specimen

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Attrition/Abrasion Test

• The sample of stone is broken into pieces of about 60mm in size.• Such pieces of weighing 50 N are then put in Deval’ s attrition testing

machine.• The cylinder is then closed and their axes make an angle of 300 with

horizontal.• The cylinder s are then rotated for 5 hrs at rate of 30 rpm.

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• The contents are then taken out of cylinder and passed trough 1.5 mm mesh.

• The quantity of material retained on sieve is then weighed.• The % wear is then found as : % wear=

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Deval’s Attrition Testing Machine

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Impact Test

• Impact test is carried out to determine the toughness of stone.• A cylinder of diameter 25mm and height 25mm is taken out from

the sample of stone, and weighed.• Then it is placed in Dorry’s testing machine and pressed with a load

of 1250gm.

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• The annular steel disc of the machine is then rotated at a speed of 28 rpm.

• During rotation, coarse sand of standard specification is sprinkled on top of the disc.

• After 1000 revolutions, the specimen is taken out and weighed.• Coefficient of Hardness is found by:

Coefficient of Hardness= 20 – loss in weight in gm

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3

Other Tests• Smith test

• Acid test

• Freezing and thawing test

• Fire resistance test

• Electrical resistance test

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Quarrying of Stones

Quarrying and Dressing

• Quarrying: An art of extracting from the rock beds stones of different varieties used for general building work and broken stones for roads and concrete work, etc.

• Quarry: The place from which stone is obtained by digging or blasting etc.

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Quarrying Tools

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Quarrying Methods

• Digging or Excavating Method. Stones buried in earth or under loose overburden are excavated with pick axes, crow bars, chisels, hammers, etc.

• Heating Method. is most suitable for quarrying small, thin and regular blocks of stones from rocks, such as granite and gneiss.

• A heap of fuel is piled and fired on the surface of rock in small area.

• The two consecutive layers of the rock separate because of uneven expansion of the two layers.

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• The loosened rock portions are broken into pieces of desired size and are removed with the help of pick-axes and crow-bars.

• Sometimes, intermediate layers are to be separated from the top and bottom layers.

• In such a case, the intermediate layer is heated electrically and the expansion separates it from the other two.

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Quarrying Methods

• Wedging Method. This method of quarrying is suitable for costly, soft and stratified rocks such as sandstone, limestone, laterite, marble and slate.

• About 10–15 cm deep holes, at around 10 cm spacing, are made vertically in the rock.

• Steel pins and wedges or plugs (conical wedges) and feathers (flat wedges) are inserted in them.

• These plugs are then struck simultaneously with sledge hammer.

• The rock slab splits along the lines of least resistance through holes.

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Quarrying Methods

• In case of soft rocks, dry wooden pegs are hammered in the holes and water is poured over them.

• The pegs being wet swell and exert pressure causing the rocks to crack along the line of holes.

• Then, the wedges are placed on the plane of cleavage (the joint of two layers) on the exposed face of rock and are hammered.

• The slab is completely detached and taken out with the help of crow bars and rollers.

• In this method, the wastage is minimum and the slabs of required size and shape can be quarried.

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Quarrying Methods

Quarrying by

wedging

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Quarrying by wedging

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Quarrying by wedging

• Blasting Method. Hard and compact rock is blasted out using explosives techniques comprising boring, charging, tamping and firing.

• Boring. Drilling of holes in rock using jumper, manual drilling or machine drilling using pneumatic (using air pressure to move or work) or mechanical power

• Charging. Placing of required quantity of explosive charge in the hole at desired location. Quantity depends upon explosive strength, blasting method, number of holes, type and mass of rock

• Gunpowder or Dynamite explosive (gms) = Square of length of line of least resistance (m) / 0.008

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Quarrying Methods

Blasting Procedure

• Tamping. Placing of priming charge, detonation cable (cordite), and sealing off the escape of gases

• Firing. detonation mechanism (electrical or non-electrical detonators) or fuse ignition

• Explosives Used in Quarrying• The composition and characteristics of the various blasting

powders and their suitability are given in Table 3.4 page 64 (Building Materials by S.K Duggal)

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Blasting Precautions

• Blasting should not be carried out in late evening or early morning. Blasting should be made public with sufficient time allowed to retire to safe distance

• 200 m radius danger zone should be marked with red flags• First aid should be made available• Proper record of number of charges prepared, fired and

exploded to account for misfires• Explosive should be handled carefully• Detonators and explosive should not be stored and kept

together• Cartridges should be handled with rubber gloves• Maximum of 10 bore holes should be exploded at a time and

that too successively and not simultaneously.

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Storage of Explosives

• The explosives should be stored in a magazine (a special type of building) which should be away from residential areas, petrol depots, etc.

• The magazine should have ventilators at high levels and should have concealed wiring.

• The magazine should be protected from lightning.

• Smoke or fire should not be allowed in the nearby area.

• Explosives should be protected from extreme heat or cold and also from moisture.

• They should be handled carefully and gently.

• The magazine should be surrounded by barbed wire and the entry should be restricted.

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Natural Bed of Stones

• It is the plane or bed occupied by a stone during its formation in a sedimentary rock.

• Natural bed has an important effect on the durability of stone.

• The stones should be so placed that the load line is at right angles to the natural bed.

• In the case of metamorphic rocks, the plane of foliation or the plane of cleavage is assumed to be its natural bed.

• It is very difficult to trace the natural bed in the case of igneous rocks and the natural bed is not given due attention.

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Position of Natural Bed of Stones in Structures

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Stone Dressing

• Pitched faced dressed – 2.5 cm edges dressed and made square

• Hammer dressed, hammer faced, quarry faced or rustic faced – dressed like a brick with 2.5 cm rough edges for use in masonry

• Rock faced and chisel drafted – chisel draft of 2.5 cm along edges

• Rough tooled – edges and corners made perfect square and true

• Punched dressed – rough tooled improved up to 2 mm• Fine tooled – fair smooth surface for ashler masonry

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Dressed Stone Surfaces

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Stone Care

Deterioration of Stones

• Rain.Rain water acts both physically and chemically on stones.The physical action is due to the erosive and transportation powers and the latter due to the decomposition, oxidation and hydration of the minerals present in the stones.

• Physical Action. Alternate wetting by rain and drying by sun causes internal stresses in the stones and consequent disintegration.

• Chemical Action. In industrial areas the acidic rain water reacts with the constituents of stones leading to its deterioration.

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Deterioration of Stones

• Frost. In cold places frost pierces the pores of the stones where it freezes, expands and creates cracks.

• Wind. Since wind carries dust particles, the abrasion caused by these deteriorates the stones.

• Temperature Changes. Expansion and contraction due to frequent temperature changes cause stone to deteriorate especially if a rock is composed of several minerals with different coefficients of linear expansion.

• Vegetable growth. Roots of trees and weeds that grow in the masonry joints keep the stones damp and also secrete organic and acidic matters which cause the stones to deteriorate. Dust particles of organic or nonorganic origin may also settle on the surface and penetrate into the pores of stones.

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Deterioration of Stones• When these come in contact with moisture or rain water,

bacteriological process starts and the resultant micro-organism producing acids attack stones which cause decay.

• Mutual decay. When different types of stones are used together mutual decay takes place. For example when sandstone is used under limestone, the chemicals brought down from limestone by rain water to the sandstone will deteriorate it.

• Chemical Agents. Smokes, fumes, acids and acid fumes present in the atmosphere deteriorate the stones. Stones containing CaCO3, MgCO3 are affected badly.

• Lichens. These destroy limestone but act as protective coats for other stones.

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Avoiding Deterioration

• Initial selection – use compact, crystalline stones instead of porous material

• Seasoning – Seasoned stones are less liable to deterioration due to frost and acids

• Natural bed – placing on natural bed provides greater strength and is detrimental to rain and frost

• Surface finish – well dressed, smooth finished and polished is more durable

• External rendering – pointing or plastering to stop rain penetration• Proper maintenance – washing, removing dirt and dust• Application of preservatives – eliminate cause of deterioration• Cure is better than medicine

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Preservation of Stones

• Stones should be kept dry with blow lamp and applied coat of paraffin, linseed oil, light paint, etc.

• Stones should be washed with water and steam to remove dirt and salt

• In industrial towns stones are preserved by application of solution of baryta, Ba(OH)2 to form insoluble barium sulphate

• Preservative treatment only slows down the decay but does not stop it. All have harmful side effects also

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Selection of Stones

• Cost – quarrying and cutting, dressing, transportation charges, etc.• Fashion & Ornamental value including color, shade, etc. specially

after prolong usage• Durability (usually overlooked and disregarded), resistance to fire

and weathering

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Selection of Stones

• Heavy engineering works bridges, piers, abutments, break waters, docks, light houses – granite (biotite, hornblende, tourmaline)

• Buildings facing the sea – granite, fine grained sandstone• Buildings in industrial area – granite, compact sandstone• Arches – fine grained sandstone• Building face work – marble, close grained sandstone• Fire resisting structure – compact sandstone• Road metal and aggregate for concrete – granite, basalt,

quartzite• Railway ballast – coarse grained sandstone, quartzite• Electrical switch board – slate, marble

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Artificial Stone

• Definition - Building material made with cement, sand and natural aggregates of crushed stone for use in place of natural stone

• Properties• Made with white cement, sand and natural aggregates of

crushed stone• Molded into most intricate forms• Cast into any size• Reinforced to desired higher strength• Desired coloring may be achieved• Desired finish may be achieved

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Artificial Stone

• Concrete block. Cast in molds for steps, window sills, masonry work, etc.

• Ransom stone. Soda silicate plus cement for decorative flooring

• Victoria stone. Granite pieces immersed in soda silicate for two months

• Bituminous stone. Provide noise, wear and dust resistant stone surfaces

• Imperial stone. Crushed granite plus cement, molded, steam cured

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Artificial Stone

• Artificial marble. Pre-cast or cast-in-situ.• These are made from portland gypsum cement and sand. In

the precast variety, the cast-stone is removed after three days. On the fifth day of casting these are treated with a solution, liquid fluorite of magnesia. It is then washed and wrapped in paper for 24 hours and then once again treated with the liquid. After one month the stone is polished by rubbing emery over the surface with a linen rag ball dipped in mixture of lime water and silicate of potash and then the process is repeated without emery. It is used for external works.

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• Cast-in-situ variety is made by laying the mix on canvas, in thickness about 1.5 mm more than the required thickness of the stone. The surface is rubbed over and the airholes are filled with mix. Grinding is done by hand or machine. The surface is then rubbed with a polishing stone. Final rubbing is done with a ball of wool moistened with alum water dipped into a 1:3 mix of hartshorn powder and diatomite.

• Garlic stone. Iron slag and cement mixture molded into flag stones, surface drains, etc.

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Building Stones

• Stones used in most historical places• Pyramids of Egypt• Taj Mahal of Agra, India• Great wall of China• Greek and Roman structures• Quaid’s Mausoleum in Karachi• Shahi mosque in Lahore• Forts at Rohtas, Jhelum• Grand Trunk Road• Lloyd’s Barrage at Sukkur

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Any Questions ???

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