Below are few points which can help you in selection of stone installation at internal and external areas of building:
Texture : A good building stones must compose fine crystalline structure which should be free from cavities, cracks or patches of soft or loose material. Stones with such texture are so strong and durable.
Toughness Index : If the value of toughness index comes below 13 in impact test, then the stone is not tough. If the value comes in between 13 & 19 then stone is said to be moderately tough and if it exceeds 19 then stone is said to be highly tough.
Hardness : As worked out in a hardness test, the coefficient of hardness should be greater than 17 for a stone to be used in a road work. If it is between 14 & 17 then it is said to be medium hardness and if it is less than 14 ,it is said to be of poor quality.
Crushing strength : For a good building stone, the crushing strength should be greater than 100 N/mm3.
Durability : A good building stone should be durable and for making stones durable, their natural bed should be carefully noted.
Appearance : Those stones which are used for face work should be decent in appearance. They should be able to protect their color for a long time.
Wear : If the wear is more than 3 in attrition test, the stone is not acceptable. For a good building stone the wear should be equal to or less than 3%.
Specific gravity : Good building stones must have specific gravity greater than 2.7
Water Absorption : We know that all the stones are more or less porous in nature but for a good building stones, percentage of water absorption by weight after 24 hours should not exceeds 0.60 .
Calibarated / uncalibrated stone: Calibrated stones requires lesser thickness of adhesive and if the stones are un-calibarated, it needs higher thickness of the adhesive.
Self-weight : The self-weight of stone should be less. as a thumb rule, stones - 32kg/Sqm can be installed using tile adhesives. If weight is more, then use mechanical clamps along with the adhesive.
Dimension: Stone should be cut to a defined size say 1:1 or 1:1.5. large rectangular stones tends to warp and crack. Installation of stone to pillars, columns and sill, jamb requires clamps. Do not install stones against to gravity.
Wear : More than 3% of wear is not so good to use. Wear up to 3% is OK and lesser than 3% wear is good.
Bio-deterioration: Stones should not under go deterioration, does not change its colour.
Strength: Good stone shall have sufficient crushing strength /compressive strength say approx. 14 MPa
Appearance / Texture: As per your choice. But it should not have open cavity, if it is then it shall be filled with transparent epoxy putty/paste.
Stone should have fire resistant, freeze that resistant not highly sensitive to moisture - in case of presence of moisture in the stone, allow it to stone-season (air dry) for sufficient time.
You can add the missed out points in below comment box.
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