Drywall (also known as plasterboard, wallboard, gypsum panel, sheet rock, or gypsum board) is a panel made of calcium sulfate wiktionary:dihydrate (gypsum), with or without additives, typically extruded between thick sheets of facer and backer paper, utilized in the construction of interior walls and ceilings. The plaster is mixed with fiber (typically paper and/or Glass (fiber) or asbestos), plasticizer, foaming agent, and various additives that can decrease mildew, increase fire resistance, and lower water absorption.
Drywall construction became prevalent in North America as a speedier alternative to traditional lath and plaster. Sackett Board was invented in 1894 by Augustine Sackett and Fred Kane, graduates of Rensselaer Polytechnic Institute. It was made by layering plaster within four plies of wool felt paper. Sheets were 36" × 36" × 1/4" (914 × 914 × 6.4 mm) thick with open (untaped) edges. Later air entrainment technology made boards lighter and less brittle, then joint treatment materials and systems also evolved. Rock lath (gypsum lath) was an early substrate for plaster. An alternative to traditional wood or metal lath, it was a panel made up of compressed gypsum plaster board that was sometimes grooved or punched with holes to allow wet plaster to key into its surface. As it evolved, it was faced with paper impregnated with gypsum crystals that bonded with the applied facing layer of plaster.
In 2002 the European Commission imposed fines totaling €478 million on the companies Lafarge (company), BPB plc, and Gyproc Benelux, which had operated a cartel on the market which affected 80% of consumers in France, the United Kingdom, Germany and the Benelux countries.
Drying chambers typically use natural gas today. To dry 1 MSF () of wallboard, between is required. Organic dispersants/plasticisers are used so the slurry will flow during manufacture, and to reduce the water and hence the drying time.Global Gypsum Magazine, January 2009, p. 18 Coal-fired power stations include devices called scrubbers to remove sulphur from their exhaust emissions. The sulphur is absorbed by powdered limestone in a process called flue-gas desulphurization (FGD), which produces a number of new substances. One is called "FGD gypsum". This is commonly used in drywall construction in the United States and elsewhere. wide panels in varying lengths to suit the application, though 48-inch is by far the most common width. Lengths up to 16 feet (4.9 m) are commonly available, though the most common length is 8 feet (2.4 m). Common panel thicknesses are , 3/4-inch (19.0 mm) and 1-inch (25.4 mm) for specific applications.
Plasterboard is commonly made with one of three different edge treatments: tapered edge, where the long edges of the board are tapered with a wide bevel at the front to allow for jointing materials to be finished flush with the main board face; plain edge, used where the whole surface will receive a thin coating (skim coat) of finishing plaster; and, finally, beveled on all four sides, used in products specialized for roofing. However, four-side chamfered drywall is not currently offered by major UK manufacturers for general use.
Drywall is cut to size, using a large T-square, by scoring the paper on the finished side (usually white) with a utility knife, breaking the sheet along the cut, and cutting the paper backing. 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 nail (engineering) or drywall screws and often glue. ''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 (construction) that traditionally was used to install drywall. Their function serves to save on material and labour expenses, to minimize call-backs due to truss uplift, to increase Efficient energy use, and to make plumbing and electrical installation simpler.
Drywall screws heads have a curved taper, which allows them to self-pilot and install rapidly without having to be punched through the paper cover. When finished driving, these screws are Countersink slightly into the drywall. Screws for light-gauge steel framing have an acute point and finely spaced threads. If the steel framing is heavier than 20-Sheet metal 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 installer conceals the seams between drywall sheets with 'joint tape' and several layers of 'joint compound' (sometimes called 'mud'), typically spread with a taping knife or putty knife. 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. This application uses blueboard, 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.
Sound transmission may be slightly reduced using regular -inch panels (with or without light-gauge resilient metal channels and/or insulation), but it is more effective to use two layers of drywall, sometimes in combination with other factors, or specially designed, sound-resistant drywall.Ballou, Glen. ''Handbook for sound engineers''. 3rd ed. Boston: Focal, 2002. Print. 75-76.
Drywall is highly vulnerable to moisture due to the inherent properties of the materials that comprise it: gypsum, paper, and organic additives and binders. Gypsum will soften with exposure to moisture, and eventually turn to a gooey paste with prolonged immersion, such as during a flood. During such incidents, some or all of the drywall in an entire building may need to be removed and replaced. Furthermore, the paper facings and organic additives mixed with the gypsum core are food for mold.
The porosity of the board—introduced during manufacturing to reduce the weight of the board, lowering construction time and transportation costs—enables water to rapidly reach the core through capillary action, where mold can grow inside. Water that enters a room from overhead may cause ceiling drywall tape to separate from the ceiling as a result of the grooves immediately behind the tape where the drywall pieces meet becoming saturated. The drywall may also soften around the screws holding the drywall in place and with the aid of gravity, the weight of the water may cause the drywall to sag and eventually collapse, requiring replacement.
Drywall's paper facings are edible to termites, which can eat the paper if they are infesting a wall cavity that is covered with drywall. This causes the painted surface to crumble to the touch, its paper backing material having been eaten. In addition to the necessity of patching the damaged surface and repainting, if enough of the paper has been eaten, the gypsum core can easily crack or crumble without it and the drywall must be removed and replaced.
In many circumstances, especially when the drywall has been exposed to water or moisture for less than 48 hours, professional restoration experts can avoid the cost, inconvenience, and difficulty of removing and replacing the affected drywall. They use rapid drying techniques that eliminate the elements required to support microbial activity while also restoring most or all of the drywall.
It is for these reasons that greenboard
Drywall is made primarily from gypsum (CaSO4•2H2O). As its chemical formula shows, gypsum contains chemically combined water (approximately 50% by volume). When gypsum panels are exposed to fire, heat is absorbed as a portion of the combined water is driven off as steam. This chemical process is called calcination. The thermal energy that converts the water to steam is thus diverted and absorbed, keeping the opposite side of the gypsum panels cool as long as there is crystalline water left to be converted into steam or until the gypsum panel is breached. In the case of regular gypsum board, as the crystalline water is driven off, the reduction of volume within the gypsum core causes large cracks to form, eventually causing the panel to fail due to loss of structural integrity. This is similar to the cracking that can be observed in a dry lake or river bed.
When used as a component in fire barriers, drywall is a passive fire protection item. In its natural state, gypsum contains the water of crystallization bound in the form of hydrates. When exposed to heat or fire, this water is vaporized, over a range of temperatures from 80° to 170 °C (see calcium sulphate), retarding heat transfer until the water in the gypsum is gone. This makes drywall an Ablation material because as the hydrates sublime, a crumbly dust is left behind, which, along with the paper, is sacrificial. Generally, the more layers of Type X drywall one adds, the more one increases the fire-resistance of the assembly, up to four hours for walls and three hours for ceilings.USG Corporation. ''The gypsum construction handbook''. 7th ed. Kingston, MA: R. S. Means ;, 2014. Print. Evidence of this can be found both in publicly available design catalogues, including DIN 4102 Part 4 and the Canadian Building Code on the topic, as well as common certification listings, including certification listings provided by Underwriters Laboratories and Underwriters Laboratories of Canada (ULC). "Type X" drywall is formulated by adding glass fibres 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 and ceilings that are required to have a fire-resistance rating.
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.[http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc41733/nrcc41733.pdf Performance of wood stud shear walls exposed to fire] 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 (engineering) of the assembly towards the fire, as that is the location where the Sublimation (chemistry) occurs, which weakens the assembly, due to the fire influence.
Cosponsored tests result in code recognized designs with assigned fire-resistance ratings. The resulting designs become part of the code and are not limited to use by any one manufacturer. However, individual manufacturers may also have proprietary designs that they have had third-party tested and approved. This is provided that 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 or in the Gypsum Association Fire Resistance and Sound Control Design Manual) and that sufficient layers and thicknesses are used. Fire test reports for such unique third party tests are confidential but may be made available to code officials upon special request.
It's important to consider deflection of drywall assemblies to maintain their assembly integrity to preserve their ratings. Deflection of drywall assemblies can vary somewhat from one test to another. Importantly, Penetrant (mechanical, electrical, or structural)s do not follow the deflection movement of the drywall assemblies they penetrate. For example, see cable tray movement in a :Image:Tray cross barrier.jpg. 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 water 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. This is motion above that caused by expansion of metallic penetrants due to heat exposure in a fire. Both types of motion occur 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, which is independent of the assemblies penetrated, can be separately arranged.
Drywall provides a thermal resistance R-value (insulation) (in US units) of 0.32 for per year). Moreover, the homebuilding and remodeling markets in North America in the late 1990s and early 2000s increased demand. The gypsum board market was one of the biggest beneficiaries of the housing boom as "an average new American home contains more than 7.31 metric tons of gypsum."[http://minerals.usgs.gov/minerals/pubs/commodity/gypsum/gypsmyb01.pdf Donald W. Olson (2002) ''Gypsum''] 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.