Drywall (also called plasterboard, dry lining, wallboard, sheet rock, gypsum board, buster board, slap board, custard board, and gypsum panel) is a panel made of calcium sulfate dihydrate (gypsum), with or without additives, typically extruded between thick sheets of facer and backer paper, used in the construction of interior walls and ceilings. The plaster is mixed with fiber (typically paper, glass wool, or a combination of these materials); plasticizer, foaming agent; and additives that can reduce mildew, flammability, and water absorption. In the mid-20th century, drywall construction became prevalent in North America as a time- and labor-saving alternative to lath and plaster. History The first plasterboard plant in the UK was opened in 1888 in Rochester, Kent. Sackett Board was invented in 1894 by Augustine Sackett and Fred Kane, graduates of Rensselaer Polytechnic Institute. It was made by layering plaster within four plies of wool felt paper. Sheets were thick with open (untaped) edges. Gypsum board evolved between 1910 and 1930, beginning with wrapped board edges and the elimination of the two inner layers of felt paper in favor of paper-based facings. In 1910 United States Gypsum Corporation bought Sackett Plaster Board Company and by 1917 introduced Sheetrock. Providing installation efficiency, it was developed additionally as a measure of fire resistance. Later air entrainment technology made boards lighter and less brittle, and joint treatment materials and systems also evolved. Gypsum lath was an early substrate for plaster. An alternative to traditional wood or metal lath was a panel made up of compressed gypsum plaster board that was sometimes grooved or punched with holes to allow wet plaster to key into its surface. As it evolved, it was faced with paper impregnated with gypsum crystals that bonded with the applied facing layer of plaster. In 1936 US Gypsum trademarked ROCKLATH for their gypsum lath product. In 2002 the European Commission imposed fines totaling €420 million on the companies Lafarge, BPB, Knauf and Gyproc Benelux, which had operated a cartel on the market which affected 80% of consumers in France, the UK, Germany and the Benelux countries. Manufacture A wallboard panel consists of a layer of gypsum plaster sandwiched between two layers of paper. The raw gypsum, , is heated to drive off the water and then slightly rehydrated to produce the hemihydrate of calcium sulfate (). The plaster is mixed with fiber (typically paper and/or glass fiber), plasticizer, foaming agent, finely