A wallboard panel consists of a layer of gypsum plaster sandwiched between two layers of paper. The raw gypsum, CaSO4·2 H2O, is heated to drive off the water then slightly re-hydrated to produce the hemihydrate of calcium sulfate (CaSO4·½ H2O). The plaster is mixed with fibre (typically paper and/or fibreglass), plasticizer, foaming agent, finely ground gypsum crystal as an accelerator, EDTA, starch or other chelate as a retarder, various additives that may decrease mildew and increase fire resistance (fibreglass), and wax emulsion or silanes for lower water absorption. The board is then formed by sandwiching a core of the wet mixture between two sheets of heavy paper or fiberglass mats. When the core sets it is then dried in a large drying chamber, and the sandwich becomes rigid and strong enough for use as a building material.
Drying chambers typically use natural gas today. To dry 1 MSF ( 1,000 square feet (93 m2) ) of wallboard, between 1,750,000 and 2,490,000 BTU (1,850,000 and 2,630,000 kJ) is required. Organic dispersants/plasticisers are used so the slurry will flow during manufacture, and to reduce the water and hence the drying time.