barch_building material-1_Types of lime, Classification of lime, comparison between fat lime and hydraulic lime, Manufacturing process slaking, Hardening – Testing and Storage, Lime putty, Precautions in handling and uses of lime.

1. LIME
 The use of lime as a cementing material has been made since ancient times.
 The Egyptians & Romans made use of this material for various constructional purposes.
 Even in India, big palaces, bridges, temples, forts, monuments, etc. were constructed with lime.
 At present, places where lime is locally available & when there is acute shortage of cement, lime
certainly provides a cheap & reliable alternative to cement.
Definitions
 Calcination:
o The heating of limestone to redness in contact with air is known as ‘Calcination’.
 Hydraulicity:
o Property of lime by which it sets or hardens in damp places, water or thick masonry
walls with no circulation of air.
 Lime:
o Due to calcinations, the moisture & carbon-dioxide are removed from it & the remaining
product is known as ‘Lime’.
o Chemical reaction – CaCo3 = CaO + Co2
 Quick lime:
o Lime obtained by the calcinations of pure limestone is known as ‘Quick Lime’ or ‘Caustic
lime’.
o It is amorphous (i.e) not crystalline & has no affinity for carbonic acid, but has affinity for
moisture.
o The quick lime as it comes out from kilns is known as the ‘lump lime’.
 Setting:
o The process of hardening of lime after being converted into paste form is known as
‘setting’.
o It is different from drying because incase of drying, water evaporates from lime & no
setting action takes place.
 Slaked lime:
o Product obtained by slaking of quick lime is known as ‘Slaked lime’ or ‘hydrate of lime’.
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2. LIME
o It is in the form of white powder & should always be used as fresh as possible because it
has a tendency to absorb carbonic acid from atmosphere & thus gets converted into
carbonate of lime.
o Such slaked lime becomes useless as it loses its setting properties.
o Therefore, it should not be kept in a damp place.
o Chemical reaction – CaO + H20 ----slaking
---- Ca (OH)2 + heat.
o The theoretical amount of water required for lime slaking is about 32%, but in practice,
the amount of water required is about 2 to 3 times more because of lime composition,
degree of burning, method of slaking & evaporation of water.
o A thin pourable suspension of slaked lime in water is known as ‘Milk of lime’.
 Slaking:
o Process in which, when water is added to quick lime, a chemical reaction takes place &
the quick lime cracks, swells & falls into a powder which is the Calcium hydrate known
as ‘Hydrated lime’.
Sources of lime
 Lime is not usually available in nature in free state.
 It is produced by burning one of the following materials;
o Lime stones from the stone hills
o Boulders of lime stones from the beds of old rivers
o Kankar (impure limestone) found below the ground &
o Shells of sea animals.
Constituents of limestone
 The properties of lime depend on the composition of the limestone from which it is produced.
 The constituents of lime stones are as follows;
 Clay:
o It is responsible for producing hydraulicity in lime.
o If excess it arrests slaking & if less, it retards slaking.
o 8% to 30% is desirable for making a good lime. Clay also makes lime insoluble in water.
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3. LIME
 Soluble Silica:
o It is essential to develop hydraulicity in lime.
o The silicates of calcium, magnesium & aluminum are responsible for hydraulicity.
o They are inert or inactive at low temperatures & become active & combine with lime at
high temperatures.
 Magnesium Carbonate:
o This constituent allows lime to slake & set slowly, but imparts more strength.
o 30% of carbonate of magnesia renders hydraulicity to lime, even in the absence of clay.
 Alkalies & Metallic oxides:
o These when present about 5% or so, develop hydraulicity.
 Sulphates:
o Its presence in small quantities, accelerates the process of setting & reduces slaking
action.
 Iron:
o If present in small quantity, it develops a complex silicate at high temperature, but
excess is objectionable.
 Pyrites:
o Undesirable to have pyrites in lime stones. Such lime stones should be rejected.
Classification of lime
 Lime obtained by calcinations of limestone is classified as;
o Fat lime
o Hydraulic lime
o Poor lime
Fat lime
 This lime is also known as High Calcium lime, Pure lime, Rich lime or White lime.
 It is popularly known as Fat lime.
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4. LIME
 It slakes vigorously & its volume increases about 2 to 2 ½ times the volume of quick lime.
 It is prepared by calcining pure lime composed of 95% of calcium oxide.
 Impurities in such limestone are less than 5%.
Properties
 Hardens very slowly
 High degree of plasticity
 Soluble in water
 Colour is perfectly white
 Sets slowly in presence of air, and
 Slakes vigorously.
Uses
 White washing & plastering walls
 With sand, it forms lime mortar which is used for brickwork & stonework.
 With surkhi, it forms lime mortar used for thick masonry walls, foundations, etc.
 (surkhi: powder obtained by grinding of burnt brick).
Hydraulic lime
 This lime is also known as ‘Water lime’ as it sets under water.
 It contains clay & some amount of ferrous oxide & depending upon the percentage of clay,
hydraulic lime is divided as;
o Feebly hydraulic lime
o Moderately hydraulic lime
o Eminently hydraulic lime
Properties
 Increase in percentage of clay makes slaking difficult & increases the hydraulic property.
 With 30% of clay, hydraulic lime resembles natural cement.
 Can set underwater & in thick walls with no free circulation of air.
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5. LIME
 Colour is not perfect white.
 Forms a thin paste with water & does not dissolve in it.
Uses
 Used for plaster works
 Hydraulic lime is ground to a fine powder & then mixed with sand & kept aside for 1 week.
 It is grounded again & then used for plastering work.
Poor lime
 It is also known as ‘Impure lime’ or ‘Lean lime’.
Properties
 Contains more than 30% of clay & slakes very slowly.
 Forms a thin paste with water but does not dissolve in it.
 Sets or hardens very slowly & has poor binding properties.
 Colour is muddy white.
Uses
 It makes a very poor mortar, that can be used for inferior type of work or places where good
lime is not available.
Building lime classification
 Class – A
o It is eminently hydraulic lime used for structural purposes & is supplied in the hydrated
form only.
 Class – B
o It is the semi – hydraulic lime used for masonry work & is supplied as ‘Quick lime’ or as
‘Hydrated lime’.
 Class – C
o It is fat lime used for plastering, white washing & supplied in hydrated or quick form.
 Class – D
o It is dolomitic lime used similar as class – C lime.
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6. LIME
 Class – E
o It is kankar lime used for masonry works & supplied as hydrated lime.
 Class –F
o It is siliceous dolomitic lime used for plastering & supplied as quick & hydrated lime.
Manufacture of lime
 3 distinct operations are involved in the manufacture of lime;
o Collection of limestone
o Calcinations of limestone
o Slaking of limestone.
Collection of limestone
 The lime stones with 5% impurities are collected at site of work.
 It is desirable to use pure carbonate of lime in the manufacturing process of fat lime.
Calcination of limestone
 The calcination’s or burning of lime stones can be achieved either in kilns or clamps.
 Clamps are temporary structures whereas Kilns are permanent structures that may be
intermittent type or continuous type.
 The fuel required for calcinations consist of charcoal, coal, firewood or coal ashes & initial firing
is achieved with few chips of dry wood or cow-dung cakes.
Clamps
 The ground is leveled & cleaned.
 The lime stones & fuel (incase of wood) are placed in alternate layers, whereas, if fuel (is coal or
charcoal), it is mixed with lime stones & placed in a heap form.
 The sloping sides are covered with mud plaster to preserve heat as much as possible.
 It is then fires from bottom & a small opening is provided at top for draught.
 When the blue flame at top disappears, it indicates the completion of the process.
 The clamp is then allowed to cool down & pieces of quick lime are handpicked.
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7. LIME
 It is adopted to manufacture lime on a small scale.
Disadvantages
 Uneconomical to manufacture lime on a large scale.
 Loss of heat is considerable as mud plaster cracks by heat inside & allows heat to escape.
 Quality of lime produced is not good,
 Quality of fuel required is more.
Intermittent Kilns
 These are of various patterns & sizes & shapes depending on the practice.
 2 important types are
o Intermittent Flame Kiln &
o Intermittent Flare Kiln.
Intermittent Flame Kiln
 Alternate layers of limestone & fuel are arranged in kiln.
 Horizontal & vertical flues are suitably formed & top of kiln is covered with unburnt material.
 The kiln is ignited from the bottom & lime stones are allowed to burn for 3 days or so.
 The kiln is then cooled & unloaded.
 The process is the repeated.
Intermittent Flare Kiln
 In this type, a rough arch of selected big pieces of lime stones are formed & smaller pieces of
lime stones are packed over this arch.
 The fuel is placed below the arch & thus is not allowed to come into contact with limestone.
 When fuel is ignited, only the flame comes into contact with limestone.
 When the lime stones are burnt, the kiln is cooled & unloaded.
 The process is then repeated.
 This type of kiln is easy to manage & produces lime of better quality as lime stones are not
mixed with fuel & the finished product does not contain ashes.
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8. LIME
Continuous Kiln
 There are various types, sizes of such kilns depending on practice in the locality.
 The 2 important types of Continuous Kilns are;
o Continuous Flame Kiln
o Continuous Flare Kiln
Continuous Flame Kiln
 It is in the form of a cylinder with diameters of 1.8m, 2.3m & 1.4m of top, middle & bottom
portion resp.
 Widening of middle portion is done to accommodate hot gases of combustion.
 The mixture of lime stones & fuel are fed from the top & the bottom is covered by grating.
 The Kiln is partially above the ground & partly below ground.
 A loading platform is provided at the top.
 The inner surface of the kiln is covered with fire-brick lining & to facilitate cleaning of the grating,
a rake hole is provided.
 After burning, the lime is collected sat the bottom & is removed through access shaft.
 As the level of material inside the kiln falls, the required quantity of mixture of limestone & fuel is
fed from top.
 A roof may be provided at top to protect the kiln.
Continuous Flare Kin
 This kiln consists of 2 sections – upper & lower.
 The upper section serves as storage of limestone & the lower portion is provided with fire-brick
lining.
 A small quantity of fuel is mixed with limestone & ignited.
 Fuel is then fed through shafts around the upper & lower sections of the kiln.
 Lime stones are fed from the top & the calcined material removal is done through a grating
placed at the bottom of kiln.
 A roof is provided at top to protect the kiln.
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9. LIME
 There is considerable saving of time & fuel in this kiln, as the fuel does not come in contact with
lime stones.
 Initial cost is high & thus these are adopted to manufacture lime on a large scale.
Facts to be remembered during the process
 Dark red colour indicates completion of burning process & presence of Co2.
 Burnt limestone should be withdrawn from kiln as soon as Co2 is driven off & colour changes to
a brilliant white.
 Over burning or under burning should be avoided during burning of stones. Ideal temperature is
800°C & for several hours.
 Heating should be gradual as sudden heating results in blowing of stones to pieces.
 Imperfectly calcined lime does not slake with water & is referred to as ‘Dead-burnt’ lime.
 Lime stones should be broken to suitable sizes before they are burnt.
 Fat lime stones – 200mm to 250mm
 Hydraulic lime stones – 75mm to 100mm.
 Quantity of fuel for burning should be carefully proportional.
Slaking of burnt lime
 The objects of slaking are;
o To ensure soundness (i.e.) bring about volumetric stability.
o To ensure plasticity
 The common methods employed for slaking are;
o Air slaking
o Basket slaking
o Platform slaking
o Tank slaking
Air Slaking
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10. LIME
 Quick lime obtained is exposed to atmosphere for slaking
 This is known as ‘Natural slaking’ or ‘Air slaking’ & is a very slow process.
 Other 2 methods of slaking are;
Slaking to paste
 In this method, quick lime is spread evenly of 150mm depth in a wooden or masonry basin.
 Water in sufficient quantity is then poured over the layer till the quick lime submerges.
 Excess water retards slaking & less water results in unsatisfactory slaking.
 The basin is covered with wooden planks to preserve heat & ensure proper slaking.
 Stirring is not required & slaking is completed in 10 minutes.
Slaking to powder
 In this method, the quick lime is slaked to powder form by 2 ways;
I method: (Basket slaking)
 Quick lime is broken to pieces of sizes 50mm.
 It is then immersed in water for a considerable time in a basket.
 The basket with lime is then removed from water & the lime pieces are thrown on a wooden or
masonry platform in a heap form.
 Quick lime crumbles & falls as powder.
II method: (Platform slaking)
 Quick lime is spread in layer of 150mm depth on a wooden or masonry platform.
 Water is sprinkled above this layer from a water can or vessel with perforated nozzle.
 Quick lime thus swells & crumbles into powder from.
 This method is generally adopted to slake quick lime obtained from the shells.
Tank slaking
 2 brick-lined tanks are constructed, one generally at the ground level 45cm deep & the other
tank is made adjacent to the first one, but at a lower level (below ground) usually 60cm to 75cm
deep.
 The first tank (at ground level) is filled half with water & sufficient quicklime is added to fill the
tank to half the level of water.
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11. LIME
 It may be noted that lime should always be added to water & not water to lime.
 The lime is then stirred with no part of lime to be exposed above water.
 As lime slakes, the temperature increases & water begins to boil. Thus additions of lime & water
are made in small quantities with constant stirring so as to maintain the required temperature
(85°C - 98°C).
 The operation is continued until the required quantity of lime or whole of lime has been slaked.
 The lime suspension (milk of lime) in the state of suspension is then allowed to pass through a
sieve & flow into the second tank at lower level.
 The particles of lime settle down & water gets partly absorbed, partly evaporated & remaining
surplus water is removed.
 The putty, prior to use, is allowed to mature in the tank for 2 to 3 days & by doing so, the
complete slaking is ensured & the workability of the putty improves.
Manufacture of Natural Hydraulic Lime
 3 distinct operations are involved in the manufacture of natural hydraulic lime.
o Collection of kankar
o Calcinations of kankar, and
o Slaking & grinding of burnt lime.
Collection of Kankar
 Kankar is an impure limestone & it is used for manufacturing natural hydraulic lime.
 It is available in 2 forms, nodular & blocks.
 Nodules are found either on surface of ground or slightly below ground level.
 They are easy to collect & are superior material for manufacturing natural hydraulic lime,
because
 It can withstand heat & rain without disintegration
 It contains higher % of clay & thus better hydraulic properties.
 The blocks of kankar are found form the underground strata below or near river banks or
streams.
 Thicknesses of blocks are usually 50mm to 300mm.
 Nodules or blocks of kankar are quarried with pick-axes or crowbars.
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12. LIME
 It is the cleaned of mud or earth & converted to suitable sizes.
Calcinations of Kankar (burning)
 Calcinations of kankar to bright red heat are done either in clamps or kilns as manufacture of fat
lime.
Slaking & Grinding of burnt lime
 The slaking of hydraulic lime occurs very slowly.
 Thus quick lime is ground dry before water is added for slaking.
 Grinding of quick lime can be done;
o By hand with the help of wooden beaters, or
o By mills working with bullocks or steam power, or
o By special machines
Differences between slaking of fat lime & hydraulic lime
Fat Lime Hydraulic Lime
 Required quantity of water for slaking is
added at time
 Required quantity of water for slaking is
gradually added through slaking
 1 part of Fat lime when slaked is
converted into 1 ½ parts in paste form
& 2 parts in powder form
 1 part of Hydraulic lime when slaked is
converted into 1 part in paste form & 1
½ parts in powder form.
 Quantity of water required for slaking is
more
 Quantity of water for slaking is less
 Time taken for slaking is about 3 to 4
hours.
 Time taken for slaking is about 12 to 48
hours.
Manufacture of Artificial Hydraulic Lime
 Artificial hydraulic lime can be prepared when natural raw material is not suitable for the
manufacture of hydraulic lime.
 Fat lime may be converted into hydraulic lime by addition of clay in required proportion.
 2 methods of preparing artificial hydraulic lime are;
o Conversion of soft limestone
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13. LIME
o Conversion of hard limestone
Conversion of Soft Limestone
 Limestone of soft quality, such as chalk, is ground & converted into powder form.
 It is then mixed with required proportion of clay & burnt in a kiln & slaking is carried out as in the
manufacture of natural hydraulic lime.
Conversion of Hard Limestone
 Limestone of hard quality is first burnt & slaked.
 To this slaked lime, required portion of clay is added.
 This mixture is converted into balls of suitable sizes & after drying, these balls are burnt in kiln.
 Slaking is then done as in the manufacture of natural hydraulic lime.
 As this lime is produced after burning twice in kiln, it is also known as ‘Twice-kilned lime’.
Precautions to be taken in handling lime
 Following precautions are to be taken while handling lime to avoid accidents;
 Contact with water: quick lime should not be allowed to come in contact with water before
slaking.
 Facilities for workers:
o Workers should be provided with googols & respirators as lime dust causes irritation.
o They should also be provided with rubber gloves, gum boots & skin protective cream as
lime causes skin burns, esp. when skin is moist.
 Fire hazard: As quick lime gives out immense heat while slaking, suitable measures should be
taken for any fire hazard.
 Instructions to workers:
o Workers handling lime – wash exposed parts of their body with abundant fresh water.
o Workers handling milk of lime which is hot – oil their skin daily to avoid burns.
Uses of lime: used as;
 Chemical raw material in the purification of water & for sewage treatment.
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14. LIME
 Flux in the metallurgical industry
 Matrix for concrete & mortar.
 Refractory material for lining open-hearth furnaces.
 Production of glass
 Making mortar for masonry work
 Plastering of walls & ceilings
 Production of artificial stone, lime – sand brick, foam – silicate products, etc.
 Soil stabilization & improving soil for agricultural purposes.
 White washing & as a base coat for distemper.
 When mixed with Portland cement, can be used in place with costly cement mortar.
Tests for lime stones
 Lime stones are tested to determine the quality of lime by detailed chemical tests in a
laboratory.
 The following practical test are made for general information;
 Physical properties
 Heat test
 Acid test
 Ball test
 Visual inspection
 Soundness test
 Workability test
 Transverse strength test
 Compressive strength test
 Impurity test
 Plasticity test
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15. LIME
Physical properties
 Pure limestone is indicated by white colour
 Hydraulic limestone id indicated by bluish grey, brown or some dark colour, tastes clayey &
gives out earthy smell.
 Presence of lumps gives an indication of quick lime or un-burnt limestone.
Heat test
 A piece of dry limestone is weighed & heated in an open fire for a few hours & a sample is
weighed again.
 The loss of weight indicates the amount of calcium carbonate in limestone is worked out.
Acid Test
 A teaspoon of powdered lime is taken in a test tube & dilute hydrochloric acid is poured in it,
stirred & kept standing with its contents for 24 hours.
 If there is vigorous effervescence & less residue formation, calcium carbonate is high –
indicates pure limestone.
 If there is less effervescence & more residue formation, calcium carbonate is less – indicates
impure or hydraulic limestone.
 If a thick gel is formed – indicates class – A of lime
 If gel is not thick & tends to flow – indicates class – B of lime.
 If no gel is formed – indicated class – C of lime.
Ball Test
 Stiff lime balls of about 40mm size are made by adding enough water & left undisturbed for 6
hours.
 The balls are then placed in a basin of water.
 If there is slow expansion & disintegration within minutes after placing in water – it indicates
class – C lime
 If there is little or no expansion & numerous cracks – it indicates class – B lime.
Visual inspection
 A sample of lime is examined for its colour & lumps.
o White colour – fat or pure lime.
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16. LIME
o Lumps of lime – quick lime or un-burnt lime.
Chemical Analysis
 The analysis determines the cementation & hydraulic properties of lime.
 Cementation value of lime = 2.8A+1.1B+0.7C
D + 14 E
Where, A = silica oxide content (SiO2)
B = aluminium oxide content (Al2o3)
C = ferric oxide content (Fe2o3)
D = calcium oxide content (CaO)
E = magnesium oxide content (MgO)
Soundness test
 The test is done to find the quality, (i.e.) the unsoundness or disintegration property of lime
using the Le-chatelier apparatus.
 To test hydrated lime;
 Cement, hydrated lime & sand (1:3:12) are mixed in the cylinder of the Le-chatelier apparatus &
is covered with a glass sheet & left for an hour.
 The distance between the indicator pointers is measured.
 The apparatus is then kept in damp air for 48 hours & is then subjected to steam for 3 hours.
 The sample is cooled to room temperature & the distance between the pointers is measured
again.
 The difference in two measurements should not be more than 10mm.
 To determine the soundness of fat lime;
 Pats are prepared by mixing 70g of hydrated lime, 10g of POP & 70ml of water.
 The pats are subjected to steam & then tested for disintegration, popping ^ piping & if any of
these occur, the lime is considered to be unsound.
 This test is also known as ‘Popping & Piping test’.
Workability test
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17. LIME
 A handful of mortar is thrown on the surface on which it is to be used & the area covered by the
mortar & its quantity is recorded along with its sticking quality.
 This data indicates the workability (if sticks well – workability is good) of the lime mortar & is a
very crude field test performed with actual mortar.
Transverse Strength test
 25 x 25 x 100mm specimens are cured for 28 days at 90% HUMIDITY.
 They are immersed in water for 30 minutes, taken out & placed on two parallel rollers, 80mm
apart & load is applied uniformly starting from 0 increasing at a rate of 150 N/minute through a
3rd
roller of same size, at a midway point between the two, till the specimen breaks.
 Modulus of rupture of test specimen, m = 3Ws = 0.0768w
2 bd2
Where, m = modulus of rupture of the specimen in N/mm2
w = breaking load in N
s = spacing between the rollers in mm
b, d = the width & depth (each 25mm) of the specimen in mm.
 Minimum value should be 1.05 N/mm2
for class – A lime, and
0.7 N/mm2
for class – B lime.
Compressive Strength test
 12 cubes of 50mm size are made from standard lime –sand mortar & are kept undisturbed for
72 hours at room temperature (27˚C ± 2˚C)
 They are then taken out of the mould & kept in open air for 4 days.
 6 of the 12 cubes are cured for 7 days & tested in a compressive testing machine & the balance
6 cubes are cured for 21 days & tested.
 The load is steadily & uniformly applied, from 0 increasing at the rate of 150 N/minute & the
crushing load is divided by the area of the cube denotes the compressive strength of mortar.
Impurity test
 A known weight of lime is mixed with water in a beaker & the solution is decanted.
 The residue is dried well in hot sun for 8 hours & then weighed.
 If residue is less than 10% - lime is good
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18. LIME
10% - 20% - lime is fair
above 20% - lime is poor
Plasticity test
 The lime is mixed with water to a thick paste & left overnight.
 It is then spread on a blotting paper with a knife to test its plasticity.
 Good lime is plastic in nature.
Lime putty
 More popularly known as Calcium hydroxide, it is used as a base material for a number of
different applications in building construction.
 It is prepared by mixing lime chalk with required quantity of water & heated to a high
temperature that helps the mixture to thicken.
 Once the desired consistency is reached, lime putty is allowed to settle & mature over several
methods.
 In order to keep the product from drying out, a thin layer of water is applied over the top level of
the putty & the container is sealed.
 It can be used in a thick composition for plastering & grouts & also as the base for a plastering
technique.
Storing lime
 Lime reacts to the moisture present in the atmosphere & that from the ground.
 Hence, it should be stored with utmost care & so following precautions should be followed
properly;
o Should be stored in properly insulated (against moisture) container & off the ground.
o When delivered as hydrated lime – kept dry, stored under cover & off the ground.
o When delivered as quick lime – should be used as soon as possible positively within a
week.
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19. LIME
o Lime putty stored without any deterioration for many weeks & actually improves by
keeping. (Maximum storage – 14 days).
o (Deterioration is caused due to the action of the atmosphere moisture on un-slaked
lime).
o In case of semi-hydraulic lime – putty must not be stored for more than 3 days of its
preparation.
o In case of hydrated eminently hydraulic lime – coarse stuff & putty should be used within
12 hours.
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