Selection of Stones - K. Vikram Rastogi - President, Stone
Article Date: 01.07.2018
Granite, marble, sandstone, limestone, slate and quartzite from different locations in India have different technical properties. For selecting a stone for a given application, it is necessary to examine the technical data of each stone. The following physico-mechanical characteristics of stones must be considered:-
• Water absorption
• Compressive strength
• Frost resistance
• Resistance to bending
• Abrasive resistance
• Resistance of surface polish against weathering
• Coefficient of linear expansion
For internal applications, technical data on water absorption, density, abrasive resistance and resistance of surface polish with human movement are important.
For external application of stones, testing of various parameters, especially in humid climates is very significant. Water absorption, compressive strength, frost resistance, density, abrasive resistance and resistance of surface polish against weathering are important factors. Resistance to bending and compressive strength must be considered for stones when used as a structural member.
In hot countries use of stones in exterior applications, changes the physical appearance including colour with time. There is a slight expansion and contraction as well and, therefore, coefficient of linear expansion must be considered especially in desert climate where temperature may vary drastically from 20o C in the night to over 50o C in the day.
Porosity and Water Absorption
Porosity is related to water absorption and density of the stone. The higher the porosity, higher is the absorption of water. Depending on the application, one should refer to the porosity scale.
Life Time of Natural Stone
Life time of natural stone is almost eternal. Pyramids in Egypt are almost 4,000 years old. Temples in India and Cambodia were constructed in natural stones which are almost 2,000 years old. All these manmade constructions are almost 1,000 to 3,500 years old. Cathedrals, temples, mosques, palaces, imposing buildings including monuments have been constructed in the last 2,000 years. All these have withstood the extreme vagaries of nature due to climatic changes.
Natural Stone for Sustainability
Sustainability in natural stone is best understood in the context of thinking of lifecycle. This would mean analyzing factors like preparation of raw materials, manufacture of pre-products, the production phase, end of life disposal, etc. Impact assessment includes energy consumption, raw material consumption, greenhouse effect, acidification, environmental toxins, waste etc. Natural stone has already been made over hundreds of millions of years. It is mined now and the processing is done by physical means. The sub-products can be recycled. The burden on the environment is low thus making natural stone the ideal hard floor covering material, when sustainability and green materials are considered. Natural stone in its sawn, honed or semi-polished form when used for wall cladding produces less carbon dioxide emissions as compared to glass panels. Thus, granite or marble slabs are much greener than glass panels used on high rise buildings.