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Granite slabs are an igneous rock with grains, which is a form from the slow crystallization of magma below Earth’s surface. Granite slabs are composed mainly of quartz and feldspar with small amounts of mica, amphiboles, and other minerals. It is generally available in the chunk, but it delivers on-site in the form of tile or slab. Granite slabs are used for flooring, stairs, facing, countertops, table tops, wall dados, door/window sill-jamb, skirting, kitchen platforms, etc.
The granite quality usually deferrers significantly from place to place, sometimes even at the same place, there is a large variation in shading, pattern or design of slab.
Here are some best ways to check the granite quality:
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01. The size of Granite slabs should be square, rectangular or as per consumer need. The dimension should be as per actual size and tolerance should not exceed 1mm in length and breadth and thickness tolerance should not exceed 15% of actual thickness. Minimum 15 to 20 mm thickness is required for any kind of construction work.
02. It should be uniform in colour, homogeneous crystalline texture, and uniform in thickness.
03. It should be hard, sound and dense. Hardness should be checked by pressing the stone with some hard object, if chips of stone will split from slab it should be rejected.
04. It should give clear ringing sound when struck. It should be water cut having no circular mark on the back of the slab.
05. It should be checked for polishing quality and cutting, and it should have one face properly polished and edges must be straight and perfectly at a right angle by means of machine or hand cutting.
- It should be checked by scraping the surface with a coin for polishing quality and if it leaves scratches than it means the polishing should be of poor quality as good polish enhances the life of granite.
06. The diagonal of Granite stone slabs should be perfect and should measure same in length.
07. The top layer should be uniform and straight and it should be free from cracks, broken edges, holes and cavities. The corner should be sharp and straight.
08. Colour should be checked by rubbing with cloth dipped in kerosene or petrol, if cloth brings colour then artificial colour must be present on it. It should be rejected.
09. Kitchen granite should be checked for porosity by dropping 3 to 4 droplets of lemon juice (citric acid) on top of granite surface.
- If kitchen granite slabs absorbs lemon juice quickly, it means granite has high porosity and hence it is not of high-quality granite.
- If calcite is present in excess amount then lemon juice droplets leaves white stain on top of kitchen granite surface, it will indicate granite is not of high quality.
Above are basically field test to find out the granite quality. Approval of material (Granite slabs) should be done by carrying out laboratory test in the laboratory.