What are the main causes of stone decay in buildings?

Decay is caused by physical agents (temperature changes, moisture), chemical agents (atmospheric acids, salts), and biological agents (moss, algae, bacteria). (Clause 3)

How can organic growth like moss and algae be removed from stone surfaces?

Treat the surface with a dilute solution of ammonia (20-50 g/litre) or a fungicide like chloramine T (1g/100ml), followed by brushing and washing. (Clause 4.3.1)

What is a 'preservative' for stone as per this code?

A treatment applied to the stone surface to make it more resistant to weathering, such as applications of oils, waxes, paints, or silicofluorides. (Clause 5)

How should iron stains be removed from sandstone or granite?

Apply a poultice made of sodium citrate, glycerine, and warm water, covered with a plastic sheet for 1-2 hours, then scrape and wash. (Clause 4.3.4)

IS 8759

: 1977

Code of practice for maintenance and preservation of stones in building

CurrentSpecializedCode of PracticeArchitectural · Stones

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This code of practice provides guidance on the maintenance and preservation of natural stones used in buildings. It covers the agents that cause stone decay, various methods for cleaning different types of stains and biological growth, and techniques for preservation and restoration.

Code of practice for maintenance and preservation of stones in building

Quick Reference Values

Ammonia solution for general cleaning20 to 50 g per litre of water

Chloramine T solution for organic growth removal1 g in 100 ml of water

Hydrofluoric acid concentration for sandstone1 part acid to 10 parts water

Silicofluorides for preservation (aqueous solution)5 to 10 percent

Ammonium chloride concentration for poultice20 g per litre of water

Practical Notes

Always test any cleaning or preservation method on a small, inconspicuous patch before applying it to the entire surface to prevent irreversible damage.

The choice of method is highly dependent on the type of stone (e.g., acidic cleaners should not be used on limestones or marbles).

Sand-blasting is generally discouraged as it can abrade the protective skin of the stone, accelerating future decay.