How long should fat lime (Class C) putty be matured before use?

It should be allowed to mature for a minimum of 2 to 3 days to ensure all particles are fully hydrated.

What is the key difference when slaking semi-hydraulic lime (Class B) vs fat lime?

Semi-hydraulic lime requires less maturing time (around 12 hours) and should be used relatively quickly, as it can slowly set under water.

What safety precautions are required during slaking?

Workers must use protective gear such as goggles, rubber gloves, and boots due to the highly caustic nature and intense heat generated during the slaking of quicklime.

IS 1635

: 1992

Code of practice for field slaking of building lime and preparation of putty

CurrentSpecializedCode of PracticeMaterials Science · Building Limes and Gypsum Products

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This code covers the recommended procedures for the field slaking of building quicklime and the preparation of lime putty. It specifies the equipment, methods, and maturing times required to ensure complete hydration and prevent defects like pitting or popping in finished plaster or mortar.

Code of practice for field slaking of building lime and preparation of putty

Quick Reference Values

Minimum maturing time for Class C (fat lime) putty2 to 3 days

Minimum maturing time for Class B (semi-hydraulic) putty12 hours

Sieve size for screening milk of lime (coarse impurities)3.35 mm IS Sieve

Practical Notes

Always add lime to water gradually, rather than water to lime, to prevent violent exothermic reactions and dangerous splattering.

Ensure the putty is properly matured; using un-matured putty can lead to 'popping' or 'pitting' in plaster due to delayed hydration of unslaked particles.

During maturation, lime putty should be protected from drying out by maintaining a thin layer of water over its surface.