These are an impure variety of siliceous clays containing more calcareous impurities along with sand and other vegetable impurities. These clays are mainly used for making tiles and bricks. The colour varies from yellow to brown. The excavated clay is stored in an open yard for quite a long time and exposed to weathering conditions. This improves the plasticity and workability of the clay. In some places a small amount of barium carbonate solution is added to the clay to convert the soluble calcium compounds in to insoluble calcium compounds. This reduces the scumming problem of tiles and bricks while in usage. Since it is readily available in the top surface of the earth the excavation is very easy and more economical.

Posted by Saseedaran Kumaran on May 11th, 2008 at 8:07 am
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