Gypsum board, also known as drywall or wallboard, is a type of sheathing used for interior walls and ceilings. Since the mid-1940s, it has been the primary wall construction in most houses. Vertical wooden pieces frame a room providing support for the sheets of wallboard. These sheets are connected to the framing by either screws or nails, and seamed together using a special drywall compound, which leaves an even and flat surface. The result is a wall that is smooth and easy to finish.
The core of the wallboard is the mineral gypsum, or hydrous calcium sulfate. It is the main ingredient in plaster of Paris, as well as a component of cement. Gypsum mines are found across the world and large deposits have been found in the United States. In addition to this natural form, a synthetic form of gypsum is produced as a byproduct of coal-fired power plants.
The process of making gypsum board begins with the mineral being ground and combined with starch to help with adhesion. Depending on the type of wallboard being made, other trace ingredients might be added at this point. Just enough water is added to create a slurry of the right consistency. Wet gypsum slurry is then sandwiched between two heavy sheets of paper and kiln dried to make the board rigid. The large sheets of wallboard are then cut into standard sizes.
The development of this type of wallboard began as early as 1917, but it did not become popular for residential home use until after World War II. Before that time, wall construction was primarily lath, or wooden horizontal supports, covered in plaster. Plaster walls took a great deal of time to build, and professional application was usually necessary. Construction using gypsum board was much more efficient and did not require the specialized labor that plaster walls sometimes did.
Besides being a finished and supporting surface for interior walls, drywall can also provide sound insulation and help limit the spread of fire. There are many manufacturers worldwide. Most sheets measure in widths of 4 feet (120 cm), and the most commonly available lengths are 8 feet (244 cm) or 12 feet (366 cm). The typical thickness used on walls is 0.5 inch (12.5 mm) and 0.375 inch (9.5 mm) for ceilings, while sound barriers or fire protection usually require 0.625 inch (15 mm).