IS 8759:1977 is the Indian Standard (BIS) for maintenance and preservation of stones in building. 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
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Abrasive Cleaning Method | Sand blasting 'shall not be adopted unless unavoidable'. | Generally prohibited for historic stone. Gentle micro-abrasive systems are a specialized alternative. | BS 8221-1:2012 |
| Primary Preservative/Consolidant | Recommends solutions of sodium silicate ('water glass'). | Sodium silicate is generally considered inappropriate as it forms a brittle, irreversible, and non-breathable crust. Breathable consolidants like ethyl silicate are preferred after testing. | BS 7913:2013 |
| Water Repellent Treatment | Suggests application of linseed oil or wax solutions. | Strongly discouraged. These create non-breathable films that trap moisture. Breathable silane/siloxane water repellents are used instead, if deemed necessary after testing. | BS 7913:2013 |
| Repointing Mortar Composition | Recommends cement-lime-sand mixes like 1:1:6 or 1:2:9. | Recommends lime-sand mortars (e.g., Natural Hydraulic Lime or lime putty). Portland cement is avoided to ensure mortar is weaker and more porous than the stone. | ASTM E2260-18 |
| Biocidal Wash Agent | Suggests zinc or magnesium silico-fluoride (1-2% solution) or sodium pentachlorophenate. | Recommends use of proprietary, tested, and approved biocidal products. Pentachlorophenate-based products are banned in many regions due to high toxicity. | BS 8221-1:2012 |
| Acid Cleaning | Allows dilute (5-10%) hydrochloric acid on stones other than limestone/marble. | Hydrochloric acid is used with extreme caution due to risk of salt formation (e.g., calcium chloride). Phosphoric or hydrofluoric acid-based cleaners are more common, used by professionals with stringent safety and runoff controls. | ASTM C1515-19 |