Properties of building stone

Structure
                     The structure of the stone may be stratified (layered) or unstratified. Structured stones should be easily dressed and suitable for super structure. Unstratified stones are hard and difficult to dress. They are preferred for the foundation works.
Texture
                       Fine grained stones with homogeneous distribution look attractive and hence they are used for carving. Such stones are usually strong and durable.
Density
                       Denser stones are stronger. Light weight stones are weak. Hence stones with specific gravity less than 2.4 are considered unsuitable for buildings.
Appearance
                        A stone with uniform and attractive color is durable, if grains are compact. Marble and granite get very good appearance, when polished. Hence they are used for face works in buildings.
Hardness
                     It is an important property to be considered when stone is used for flooring and pavement. Coefficient of hardness is to be found by conducting test on standard specimen in Dory’s testing machine. For road works coefficient of hardness should be at least 17. For building works stones with coefficient of hardness less than 14 should not be used.
Percentage Wear
                       It is measured by attrition test. It is an important property to be considered in selecting aggregate for road works and railway ballast. A good stone should not show wear of more than 2%.
Porosity and Absorption
                      All stones have pores and hence absorb water. The reaction of water with stone causes disintegration. Absorption test is specified as percentage of water absorbed by the stone when it is immersed under water for 24 hours. For a good stone it should be as small as possible and in no case more than 5.
Weathering
                    Rain and wind cause loss of good appearance of stones. Hence stones with good weather resistance should be used for face works.
Toughness
                   The resistance to impact is called toughness. It is determined by impact test. Stones with toughness index more than 19 are preferred for road works. Toughness index 13 to 19 is considered as medium tough and stones with toughness index less than 13 are poor stones.
Resistance to Fire
                Sand stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire.
Ease in Dressing
                Cost of dressing contributes to cost of stone masonry to a great extent. Dressing is easy in stones with lesser strength. Hence an engineer should look into sufficient strength rather than high strength while selecting stones for building works.
Seasoning
                 The stones obtained from quarry contain moisture in the pores. The strength of the stone improves if this moisture is removed before using the stone. The process of removing moisture from pores is called seasoning. The best way of seasoning is to allow it to the action of nature for 6 to 12 months.