Drywall 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 sulfate (CaSO4.½ H2O). The raw gypsum (mined or FGD) must be calcined before use. Flash calciners typically use natural gas today. The plaster is mixed with fiber (typically paper and/or fiberglass), plasticizer, foaming agent, potash as an accelerator, EDTA or other chelate as a retarder, various additives that increase mildew and fire resistance (fiberglass or vermiculite), and water. This 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 in a large drying chamber, the sandwich becomes rigid and strong enough for use as a building material. Drying chambers typically use natural gas today. Depending on plant efficiency and energy costs, 25% to 45% of drywall cost today is related to energy, primarily natural gas.
Drywall is also commonly known as gypsum board, wallboard, plasterboard (USA,UK, Ireland, Australia, Lebanon), Gibraltar board or gib (New Zealand - GIB being a trademark of Winstone Wallboards), rock lath, Sheetrock (a trademark of United States Gypsum Company), gyproc (Canada, Australia, UK), pladur (Spain - after the Pladur brand), or rigips (Germany and Central Europe - after the Rigips brand), or simply board.
The most commonly used drywall is one-half-inch thick but can range from one quarter (6.35 mm) to one inch (25.4 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.
Most plasterboard is made in 1200 mm wide sheets, though 900 mm wide sheets are also made. 1200 mm wide plasterboard is most commonly made in 2400 mm lengths, though 2700 mm and 3000 mm length sheets are also commonly available.
The most commonly used thicknesses of plasterboard available are 12.5 mm (modern equivalent of half an inch), typically used for walls, and 9.5 mm (modern equivalent of three-eights of an inch), typically used for ceilings. 15 mm thick board is commonly available, and other thicknesses are also produced.
Plasterboard is commonly made with one of two different edge treatments: Tapered Edge, where the sides of the board are tapered at the front to allow for jointing materials to be finished flush with the main board face, and Straight Edge, where there is no different thickness at the side of the board.
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 mudmen, or float crew, who finish the joints and cover the nailheads with drywall compound.
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, the now-ubiquitous drywall screws.
Drywall fasteners, also referred to as drywall clips or stops, are gaining popularity in both residential and commercial construction. Drywall fasteners are used for supporting interior drywall corners and replacing the non-structural wood or metal blocking that traditionally was used to install drywall. Their function serves to save on material and labor expenses; to minimize call backs due to truss uplift; to increase energy efficiency; and to make plumbing and electrical installation simpler. Many green building and energy efficiency models suggest using drywall fasteners to conserve resources and save energy, including the U.S. Dept. of Energy.
Drywall screws have a curved, bugle-shaped top, allowing them to self-pilot and install rapidly without punching through the paper cover. These screws are set slightly into the drywall. When drywall is hung on wood framing, screws having an acute point and widely spaced threads are used. When drywall is hung on light-gauge steel framing, screws having an acute point and finely spaced threads are used. If the steel framing is heavier than 20-gauge, self-tapping screws with finely spaced threads must be used. 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.
Fire testing of drywall assemblies for the purpose of expanding national catalogues, such as the National Building Code of Canada, Germany's Part 4 of DIN4102 and its British cousin BS476, are a matter of routine research and development work in more than one nation and can be sponsored jointly by national authorities and representatives of the drywall industry. For example, the National Research Council of Canada routinely publishes such findings The results are printed as approved designs in the back of the building code. Generally, exposure of drywall on a panel furnace removes the water and calcines the exposed drywall and also heats the studs and fasteners holding the drywall. This typically results in deflection of the assembly towards the fire, as that is the location where the sublimation occurs, which weakens the assembly, due to the fire influence. When tests are co-sponsored, resulting in code recognised designs with assigned fire-resistance ratings, the resulting designs become part of the code and are not limited to use by any one manufacturer, provided the material used in the field configuration can be demonstrated to meet the minimum requirements of Type X drywall (such as an entry in the appropriate category of the UL Building Materials Directory) and that sufficient layers and thicknesses are used. Fire test reports for such unique third party tests are confidential. Deflection of drywall assemblies is important to consider to maintain the integrity of drywall assemblies in order to preserve their ratings. The deflection of drywall assemblies can vary somewhat from one test to another. Importantly, penetrants do not follow the deflection movement of the drywall assemblies they penetrate. For example, see cable tray movement in a German test It is, therefore, important to test firestops in full scale wall panel tests, so that the deflection of each applicable assembly can be taken into account. The size of the test wall assembly alone is not the only consideration for firestop tests. If the penetrants are mounted to and hung off the drywall assembly itself during the test, this does not constitute a realistic deflection exposure insofar as the firestop is concerned. In reality, on a construction site, penetrants are hung off the ceiling above. Penetrants may increase in length, push and pull as a result of operational temperature changes (e.g. hot and cold water in a pipe), particularly in a fire, but it is a physical impossibility to have the penetrants follow the movement of drywall assemblies that they penetrate, since they are not mounted to the drywalls in a building. It is, therefore, counterproductive to suspend penetrants from the drywall assembly during a fire test. As downward deflection of the drywall assembly and buckling towards the fire occurs, the top of the firestop is squeezed and the bottom of the firestop is pulled - and this is motion over and above that, which is caused by the expansion of metallic penetrants themselves, due to heat exposure in a fire. Both types of motion occur in reality because metal first expands in a fire and then softens once the critical temperature has been reached, as is explained under structural steel. To simulate the drywall deflection effect, one can simply mount the penetrants to the steel frame holding the test assembly. The operational and fire induced motion of the penetrants themselves, which is independent of the assemblies penetrated, can be separately arranged.
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. 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 was predicted to shift significantly. However, issues such as mercury release during calcining need to be resolved.
The official document (summarized below) is known as GA-214-96 "Recommended Levels of Gypsum Board Finish"
Usage: Temporary construction or when final decoration is undetermined.
Usage: Above false ceilings or other areas which are out of public view where a degree of fire and noise resistance is required.
Usage: As a substrate for tile walls and ceilings as well as in garages, warehouses, and other places where appearance is not a primary concern.
Usage: Suitable base for heavy-medium textured paint or other thick finishes.
Usage: "Standard" household and office walls. Used with light or non-textured finishes. Not suitable for harsh lighting conditions which may highlight minor imperfections.
Usage: The skim coat is a final leveling agent suitable to smooth out a surface to be used under the harshest lighting conditions that may otherwise highlight any imperfections under the finished surface. This finish is highly recommended for gloss and entirely non-textured surfaces.
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