Plaster of Paris
Plaster of Paris is calcined gypsum. Mixed with ordinary lime it is used for repairing holes and cracks in wooden or plastered surfaces, and for making moulds and ornamental works. When mixed with water its swells slightly and sets rapidly.
Gypsum is natural calcium sulphate and occurs as a soft stone which is from white to dark in colour. It is used mainly in the manufacture of cement.
Barium Plaster is employed as finishing coat to X-ray room walls, It consists of 1 part cement, 2 parts of fine and 2 parts of coarse barium sulphate powder. Thickness varies from 6 mm to 12mm.