Drywall

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For the musical group "Drywall," see Drywall (musical project)

Drywall, also commonly known as gypsum board, plasterboard (UK, Ireland, Australia, New Zealand), or rock lath, and sheetrock (a registered trademark of United States Gypsum Company<ref>"Trademarks", United States Gypsum Company. Retrieved on 2006-10-19.</ref>) is a common manufactured building material used globally for the finish construction of interior walls and ceilings.

A drywall panel is made of a paper liner wrapped around an inner core made primarily from gypsum plaster, the semi-hydrous form of calcium sulphate (CaSO₄.½ H₂O). The plaster is mixed with fiber (typically paper and/or fiberglass), foaming agent, various additives that increase mildew and fire resistance, and water and is then formed by sandwiching a core of wet gypsum between two sheets of heavy paper or fiberglass mats. When the core sets and is dried, the sandwich becomes rigid and strong enough for use as a building material.

1 Specifications (USA only)
2 Construction techniques
3 Fire resistance
4 North American market
5 Types available in the USA
6 Common drywall tools
7 See also
8 References
9 External links

[edit] Specifications (USA only)

Drywall is typically available in 4 ft (1219 mm) wide sheets of various lengths. Newly formed sheets are cut from a belt, the result of a continuous manufacturing process. In some commercial applications, sheets up to 16 ft are used. Larger sheets make for faster installation, since they reduce the number of joints that must be finished. Often, a sizable quantity of any custom length may be ordered, from factories, to exactly fit ceiling-to-floor on a large project.

The most commonly used drywall is one half inch thick, but can range from one quarter (6.35 mm) to one inch (25 mm). For soundproofing or fire resistance, two layers of drywall are sometimes laid at right angles to each other. In North America, five-eighths inch thick drywall with a one-hour fire-resistance rating is often used where fire resistance is desired.

Drywall provides a thermal resistance R-value of 0.32 for three-eighths-inch board, 0.45 for half inch, 0.56 for five-eighths inch and 0.83 for one-inch board. In addition to increased R-value, thicker drywall has a higher sound transmission class.

[edit] Construction techniques

Image:Drywall material handler.jpg

Drywall is cut to size, using a large T-square, by scoring the paper on the front side (usually white) with a utility knife, breaking the sheet along the cut, scoring the paper backing, and finally breaking the sheet in the opposite direction. Small features such as holes for outlets and light switches are usually cut using a keyhole saw or a small high-speed bit in a rotary tool. Drywall is then fixed to the wall structure with nails, or more commonly in recent years, specially designed screws. (Drywall screws have an acute point, widely spaced threads, and a curved top, allowing them to self-pilot and install rapidly without punching through the paper cover.) These screws are set slightly into the drywall. In some applications, the drywall may be attached to the wall with adhesives.

After the sheets are secured to the wall studs or ceiling joists, the seams between drywall sheets are concealed using joint tape and several layers of joint compound (sometimes called "mud"). This compound is also applied to any screw holes or defects. The compound is allowed to air dry then typically sanded smooth before painting. Alternatively, for a better finish, the entire wall may be given a skim coat, a thin layer (about 1 mm or 1/16 inch) of finishing compound, to minimize the visual differences between the paper and mudded areas after painting.

Another similar skim coating is always done in a process called veneer plastering, although it is done slightly thicker (about 2 mm or 1/8 inch). Veneering uses a slightly different specialized setting compound ("finish plaster") that contains gypsum and lime putty. For this application blueboard is used which has special treated paper to accelerate the setting of the gypsum plaster component. This setting has far less shrinkage than the air-dry compounds normally used in drywall, so it only requires one coat. Blueboard also has square edges rather than the tapered-edge drywall boards. The tapered drywall boards are used to countersink the tape in taped jointing whereas the tape in veneer plastering is buried beneath a level surface. One coat veneer plaster over dry board is an intermediate style step between full multi-coat "wet" plaster and the limited joint-treatment-only given "dry" wall.

Image:Screwgun.jpg

The name drywall derives from drywall's replacement of the lath-and-plaster wall-building method, in which plaster was spread over small wooden formers while still wet. As opposed to a week-long plaster application, an entire house can be drywalled in one or two days by two experienced drywallers, and drywall is easy enough to use that it can be installed by many amateur home carpenters. In large-scale commercial construction, the work of installing and finishing drywall is often split between the drywall mechanics, or hangers, who install the wallboard, and the tapers and mudman, or float crew, who finish the joints and cover the nailheads with drywall compound.

Because up to 17% of drywall is wasted during the manufacturing and installation processes,^{[citation needed]} disposal has become a problem. Some landfill sites have banned the dumping of drywall. Therefore, used drywall and gypsum are often dumped into the ocean where it is not known to cause harm to sea life. The EPA regulates this ocean dumping by permit. Most manufacturers with an environmental concern take back the boards from construction sites, and burn them at high temperature to eliminate the paper and bringing back the gypsum to its initial plaster state. Since recycled paper is used during manufacturing, the environmental impact is minimal. More recently, recycling at the construction site itself is being investigated.

[edit] Fire resistance

When used as a component in fire barriers, drywall is a passive fire protection item, subject to stringent bounding. It exhibits fire resistance because it is endothermic. In its natural state, gypsum contains water of crystalisation bound in the form of hydrates. When exposed to heat or fire, this water is vaporized, retarding heat transfer. Therefore a fire in one room, which is separated from an adjacent roon by a rated drywall assembly, will not cause this adjacent room to get any warmer than the boiling point until the water in the gypsum is gone. This makes drywall an ablative material. "Type X" drywall is formulated by adding glass fibers to the gypsum, to increase the resistance to fires, especially once the hydrates are spent, which leaves the gypsum in powder form. Type X is typically the material chosen to construct walls that are required to have a fire-resistance rating.

A typical fire problem: the measures taken by the plumbers and the drywallers are at cross-purposes.

Another example: this steel sleeve, a penetrant itself, causes more problems than it solves.

Penetrants have been punched and burned through drywall, compromising its integrity.

[edit] North American market

North America hails as one of the largest gypsum board users in the world with a total wallboard plant capacity of 40 billion square feet per year.<ref>Mineral Commodity Summaries, January 2006</ref> Moreover, the home building and remodeling markets in North America have increased demand for last five years. The gypsum board market is one of the biggest beneficiaries of the housing boom as "an average new American home contains more than 7.31 metric tons of gypsum."<ref>Donald W. Olson (2002) Gypsum History and production</ref>

The introduction in March 2005 of the Clean Air Interstate Rule by the United States Environmental Protection Agency requires power plants to "cut sulfur dioxide emissions by 73%" by 2018.<ref>Clean Air Interstate Rule</ref> The Clean Air Interstate Rule also requested that the power plants install new scrubbers (industrial pollution control devices) to remove sulfur dioxide present in the output waste gas. Scrubbers use the technique of flue gas desulfurization (FGD), which produces synthetic Gypsum as a usable by-product. In response to the new supply of this raw material, the Gypsum board market is predicted to shift significantly.

[edit] Types available in the USA

Regular white board
Fire-resistive ("Type X"), which comes in various ratings based on the time the product can withstand a standardized fire test. Often perlite, vermiculite and boric acid are added to improve fire resistance.
Greenboard, a drywall that contains an oil-based additive that provides moisture resistance. It is commonly used in washrooms and other areas expected to experience elevated levels of humidity.
Concrete backerboard, which is more water-resistant than greenboard.
Enviroboard, a board made from recycled agricultural materials.
Mold-resistant, paperless drywall from Georgia-Pacific.
Lead-lined drywall, a drywall used around radiological equipment