A precast gypsum product used particularly for roof construction is composed of a core of gypsum cast in the form of a plank, with wire-fabric reinforcement and usually with tongue-and-groove metal edges and ends. The planks are available in two thicknesses a 2-in plank, which is 15 in wide and 10 ft long, and a 3-in plank which is 12 in wide and 30 in long. (See ASTM C377.)
