ground gypsum crystal as an accelerator, EDTA, starch or other chelate as a retarder, various additives that may decrease mildew and increase fire resistance, 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 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 of wallboard, between is required. Organic dispersants and plasticizers are used so that the slurry will flow during manufacture and to reduce the water and hence the drying time. Coal-fired power stations include devices called scrubbers to remove sulfur from their exhaust emissions. The sulfur is absorbed by powdered limestone in a process called flue-gas desulfurization (FGD), which produces several new substances. One is called "FGD gypsum". This is commonly used in drywall construction in the United States and elsewhere. In 2020, 8.4 billion square meters of drywall were sold around the world. Specifications Australia and New Zealand The term plasterboard is used in Australia and New Zealand. In Australia, the product is often called Gyprock, the name of the largest plasterboard manufacturer. In New Zealand it is also called Gibraltar and Gib board, after the registered trademark ("GIB") of the locally made product that dominates the market there. It is made in thicknesses of 10 mm, 13 mm, and 16 mm, and sometimes other thicknesses up to 25 mm. Panels are commonly sold in 1200 × 2400 mm, 1200 × 4800 mm, and 1200 × 6000 mm sheets. Sheets are usually secured to either timber or cold-formed steel frames anywhere from 150 to 300 mm centres along the beam and 400 to 600 mm across members. In both countries, plasterboard has become a widely used replacement for scrim and sarking walls in renovating 19th- and early 20th-century buildings. Canada and the United States Drywall panels in the United States are made in widths of and varying lengths to suit the application. The most common width is . Lengths up to are common; the most common is . Common thicknesses are ; thicknesses of are used in specific applications. Europe In Europe, most plasterboard is made in sheets wide; sheets wide are also made. Plasterboard 120 cm wide is most