Drywall
Drywall is a common building material. It is also referred to as plasterboard or gypsum board or by its common trade names Sheetrock and Gyproc. It is composed of two thick paper sides with a slab of compressed gypsum between them. It is known as "dry wall" because it replaced lath and plaster, which was applied "wet". Drywall is used as wall and ceiling cladding material and typically screwed or nailed to wood or metal wall studs, often set on 16-inch or 400 millimeter centers. Drywall is not weight bearing and is not suitable for floors. However it can add shear or racking strength to a framed structure.
Drywall can be installed with the sheets lying either vertically or horizontally, horizontal being more common in North American residential construction. For added fire protection or soundproofing, sometimes two layers are installed with the long edge perpendicular to the other. Special fire-rated 5/8 inch thick drywall is also used.
After it is screwed or nailed on, drywall is usually finished by filling in the joints and nail or screw holes with joint compound, referred to as drywall "mud" by tradespeople. The joints are reinforced with paper or mesh tape imbedded in joint compound. Drywall used in office partitions is often faced with vinyl wallpaper and the joints are hidden with decorative battens or strips.
In North America, drywall is typically available as 4-foot (1220 mm) wide sheets of various lengths from eight feet to sixteen feet (2440 mm). In other countries, the typical width is 1200 mm, with lengths starting at 2400 mm and available in 300 mm increments up to 3600 mm. It comes in various thicknesses, most common being 1/2 inch (12.5 millimetres), but is also available as 1/4 inch, 3/8 inch, 5/8 inch and up to 1 inch. In metric countries, boards are typically 12 mm, 12.5 mm or 12.7 mm thick, and can range from 8 mm to 25 mm thick.
Drywall has very little water resistance. When a leaky roof or condensation wets drywall, the gypsum can dissolve away and leave just a layer of painted paper in its place. A more water resistant form has a water repellent coating on one of the paper sides. The coating is usually green and it is called green board. Green board is a cheap solution to backing tile in a bathroom. In a heavily watered area, such as a shower, it is recommended to use cement board or other substrates instead.
Drywall can also have a layer of aluminum foil on one side. This layer acts as a vapor barrier preventing the flow of moisture laden into the wall cavity, avoiding condensation and eventual mold and rot. However, the foil layer severely limits the transmission of radio waves, such as Wi-Fi signals.