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- For the musical group "Drywall," see Drywall (musical project)
Drywall (also called wallboard, gypsum board, GWB, and plasterboard) is a building material consisting of gypsum formed into a flat sheet and sandwiched between two pieces of heavy paper. As of 2005, it is the most common material used globally for the construction of interior walls and ceilings.
Some common brand names of drywall are Tablaroca®, SHEETROCK®, Gyprock®, and ToughRock®.
Raw materials in drywall
Drywall is made primarily from the semi-hydrous form of calcium sulphate (CaSO4.½ H2O) plaster created by heating ground gypsum rock (hydrous calcium sulfate). The plaster is mixed with fibre (typically paper and/or fibreglass), 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. When the core sets and is dried, the sandwich becomes rigid and strong enough for use as a building material.
Drywall types
Drywall is available in three forms:
- Regular white board
- Fire-resistive ("Type X") comes in various ratings based the time the product can withstand standardized fire test. Often perlite, vermiculite and boric acid are added to improve fire resistance.
- Green—for use in washrooms and other areas expected to experience elevated levels of humidity. This product contains an oil-based additive that provides moisture resistance.
Greenboard is water resistant drywall. Early versions had asphalt added which gave it a brown gypsum core. It is suitable for humid areas, but not areas that actually get wet. Concrete backerboard (concrete reinforced with fiberglass) should be used where actual moisture is expected. Concrete backerboard is typically used as the underlayment for ceramic tile. Enviroboard is a board made from recycled agricultural materials.
Drywall specifications
In the United States and Canada, drywall is typically available in four-foot (1220 mm) wide sheets of various lengths, commonly 8 feet (2440 mm), 9 feet, 10 feet, 12 feet, and 14 feet. The newly formed sheets are cut from a virtually endless "belt", the result of a continuous manufacturing process. In some commercial applications, sheets up to 16 feet are used. 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. Larger sheets make for faster installation, since they reduce the number of joints that must be finished, especially when the sheets are installed horizontally as is often done in American home building. Often, a sizable quantity of any custom length may be ordered, from factories, to exactly fit ceiling-to-floor on a large project, similar to the picture of sheets installed vertically shown in the upper right corner of this page.
Available thicknesses vary by country. The most commonly used drywall is about 1/2 inches thick (12 mm, 12.5 mm or 12.7 mm depending on country) thick, but can range from 6.35 mm (1/4 inch) to 25 mm (1 inch) thick. For soundproofing or fire resistance, two layers of drywall are sometimes used laid at right angles. In North America, drywall in 5/8-inch thickness with a one hour fire resistance rating is also often used where fire resistance is desired.
Drywall provides an R-value of 0.32 for 3/8" board, 0.45 for 1/2" board, 0.56 for 5/8" and 0.83 for 1" board. In addition to increased R-value, thicker drywall has a higher STC.
Construction techniques
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 and widely spaced threads and a curved top, allowing them to self-pilot and install rapidly without punching through the paper cover.) In some applications, the drywall may be attached to the wall with adhesives.
After the sheets are secured to the wall studs and/or ceiling joists, the seams between drywall sheets are concealed using joint tape and several layers of joint compound (sometimes called "mud"). 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 (actually "finish plaster") that contains some gypsum and some 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 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.
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. A later development was the use of plasterboard that replaced the wooden lath and the first of three coats (the scratch coat) of early plaster. Plaster board was usually smaller than later drywall sheets, being only about 2 foot by 4 foot pieces. Either of these methods are time consuming and labor intensive, although skilled plasterers could do the job with great rapidity. 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, 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, they are then burned at high temperature (thus burning away the paper and bringing back the gypsum to its initial plaster state). Since recycled paper is used during manufacturing, the environmental impact is minimal.
Fire resistance in drywall
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 crystalization. Prior to placement in sheet form, the gypsum was mixed with water; some of that water remains as unbound moisture which is removed during the drying process, and most of it becomes chemically bound in the form of hydrates. When exposed to heat or fire, this water is released as steam, retarding heat transfer. This is the same principle (latent heat of vaporization) that prevents a boiling pot of water from getting any warmer than about 100 degrees C (212 degrees F; at sea level) until the water is all boiled away, at which point the pot will quickly get much warmer. Therefore a fire of several hundred degrees in one room will not cause an adjacent room to get any warmer than the boiling point until the "trapped" water in the gypsum is boiled away, preventing flashover. A special fire-rated (Type X) drywall is formulated by adding noncombustible fibers to the gypsum, helping to maintain integrity at high temperatures. Since it is possible to obtain fire-resistance ratings with drywall assemblies, some residential builders at times use it to construct firewalls, which is illegal.
Common problems with fire-resistant drywall
A common problem with fire-resistance rated drywall assemblies is firestopping. Because of the staging of construction, particularly in North America, penetrants are installed first, by electricians, plumbers, etc. The drywall follows. This is routinely used as an excuse by the contractors who install electrical and mechanical services to disavow any and all responsibility for firestopping drywall penetrations, which can be particularly costly. Consequently, drywallers simply "mud up" to the penetrants and consider themselves to be quite finished. In fairness, it is unrealistic to expect drywallers to interpret mechanical and electrical drawings and specifications and expect them to allow for proper firestops.
In fire testing, drywall assemblies move back and forth and generally "relax towards the fire". Penetrants do not follow this movement, which is unique for each vendor and each system. This unique movement is considered proprietary knowledge on the part of the test submitter, which is usually the drywall manufacturer.
Images
Drywall market in North America
North America hails as one of the largest gypsum board users in the world with a total wallboard plant capacity of 40 billion sq. feet per year (U.S Geological Survey).
Gypsum board market has been changing since the introduction of the new Clean Air Interstate Rule in March, 2005 by the United States Government which demanded that all the power plants “cut sulfur dioxide (SO2) emissions by 73 percent” (EPA - Clean Air Rules of 2004) by 2018. The Clean Air Interstate Rule also requested that the power plants install new scrubbers (industrial pollution control devices) that will remove the sulfur dioxide (SO2) that is present in the output waste gas. These scrubbers use the technique of flue gas desulfurization (FGD) which is used by 27 countries worldwide and the technique is capable of removing 95% of sulfur dioxide *. FGD technique also can produce a usable by-product, synthetic Gypsum. In response to the new supply of this raw material, the Gypsum board market is predicted to shift significantly.
Moreover, the real estate market in North America has been rising for last five years as indicated on the side and new homes and high rising buildings are emerging on every bit of empty land. Gypsum board market is one of the biggest beneficiaries of the housing boom as “an average American Home contains more than 7 metric tons of Gypsum” (U.S Geological Survey). Due to the newly installed scrubbers and the housing boom, the Gypsum board market is changing at a much higher rate than expected. The shift will affect many parties including gypsum board companies, by-product suppliers, share holders, potential investors, home builders, home buyers and many others who are involved in the housing business.
Common drywall tools
- Corner trowels
- Dimpler
- Drywall screws or nails
- Electric screwdriver
- Keyhole saw or drywall router
- Taping/joint knives
- Utility knife
See also
External links
"Drywall"