Building Lime

Sources of lime; terms — quicklime, slaking, hydrated lime, milk of lime, lime putty; chemistry of calcination, slaking and setting (carbonation and hydraulic set); classification of lime — fat, poor and hydraulic limes (feebly, moderately, eminently) and IS classes; manufacture (kilns); slaking methods and storage; tests on lime (visual, acid, ball, heat, workability, impurities); pozzolanas and lime–pozzolana mixtures; uses of lime; comparison of lime and cement — with solved numericals.

Building Lime

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📑 Contents (12 sections)

Last reviewed 16 Sept 2026 · 8 min read

Lime in construction

Lime was the principal binding material before Portland cement and remains useful in mortars, plasters, whitewash, soil stabilisation and restoration of heritage buildings.

Sources: limestone, chalk, kankar (impure nodular limestone), shells (sea shells), dolomite (for magnesian lime).

Terms

Term	Meaning
Calcination	Heating limestone to a high temperature (around 900 °C) to drive off CO₂
Quicklime (caustic lime)	Calcium oxide (CaO) obtained by calcination — white, amorphous, very reactive with water
Slaking	Chemical combination of quicklime with water, with heat, hissing and swelling
Slaked lime (hydrated lime)	Calcium hydroxide Ca(OH)₂ — a fine white powder
Milk of lime	Thin suspension of slaked lime in water — used for whitewash
Lime putty	Thick paste of slaked lime and water — for plaster and mortar
Setting	Hardening of lime — by carbonation (fat lime) or by hydration of silicates and aluminates (hydraulic lime)

Chemistry of lime

FormulaReactions

Calcination:

C a C O_{3} \approx 900 ° C C a O + C O_{2}

Slaking (exothermic, volume increases):

C a O + H_{2} O \to C a (O H)_{2} + heat

Setting by carbonation (slow; needs air):

C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O

Hydraulic set: clay (silica and alumina) in limestone forms calcium silicates and aluminates on burning, which hydrate and harden like cement, even under water.

Molecular weights: CaCO₃ = 100, CaO = 56, CO₂ = 44, H₂O = 18, Ca(OH)₂ = 74.

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