Author: Haroon Khalil

The clay selected for terra-cotta should contain about 5–8% of iron oxide and about 1% of lime. Sometimes clay with high alumina content is used. To these selected clays, sand, ground glass, old terra-cotta or pottery are added. The addition of these materials provides strength and rigidity to the terra-cotta and also prevents shrinking while…

Terra-cotta is earthenware of vitrified material. It is high-quality earthenware. It is used as a substitute for stone in the ornamentation of buildings. The manufacture of terra-cotta involves the same four stages as that of tiles.

It has been discussed that earthenware is manufactured from ordinary clay burnt at low temperatures. Sometimes the clay is mixed with sand, crushed pottery, etc. Earthenware are susceptible to damage by atmospheric action since they are soft and porous. In general, they should not absorb more than about 20% of water by weight. In order…

The tiles are burnt in a kiln which could accommodate 30,000–40,000 tiles. Such kilns are partly underground and are usually provided with a roof to protect the kiln from rain. A layer of bricks is laid over the long narrow flues, and the flues are fed with wood. The bricks are so placed such that…

After two days of moulding, they are slightly beaten with a flat wooden mallet to correct the irregularity in shape due to warping. They are then kept on edges for further drying under shade for 2 days. This is done to prevent warping and cracking.

Depending on the pattern of tile to be moulded, the moulding method is selected. Wooden patterns are used for tiles which are not of uniform thickness throughout the length and are moulded in wooden plattens. The pugged clay is pressed into the mould and the tiles are taken out for drying. When the pattern of…

As stated earlier, the best blue clay for tiles is generally found beneath brick earth. Impurities such as grit, pebbles, etc. are removed from the selected clay. The clay is ground into a powder form in crushing roller mills. It is then pugged. For the preparation of superior tiles, the powdered clay is mixed with…

Manufacture of the common clay tiles involves the following processes:

(i) Glazed Ceramic Tiles They are made from special ceramic clays in two operations. In the first operation the tiles are made and fired at 1,200–1,300ºC; then they are coated with glaze, decorations, etc. Again they are fired in ovens to get opaque glazing. Wear of the glazing is based on the temperature of firing…

Tiles may be grouped under two broad categories: