Drywall

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

Drywall, also commonly known as gypsum board, plasterboard (UK, Ireland, Australia), gib board (New Zealand - GIB being a trademark of Winstone Wallboards), rock lath, sheetrock (a trademark of United States Gypsum Company^[1]), and gyprock (Canada - likely a portmanteau of "gypsum board" and "sheetrock") 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.

Specifications (USA and Canada)

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.

Construction techniques

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.

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 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.

History

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. In 1916, the United States Gypsum Company invented a 4' x 8' sheet of gypsum pressed between sheets of extremely strong paper, which they called "Sheetrock."[1] Despite being used extensively at the Chicago World's Fair in 1933-34, it was generally seen as an inferior alternative to plaster and did not catch on quickly. It gained popularily during World War II, when the war effort made labor expensive. It was reintroduced in 1952, and the suburban migration of the 1950s was fueled in part by the cheaper construction methods allowed by drywall.[2]

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 the water of crystallisation bound in the form of hydrates. When exposed to heat or fire, this water is vapourised, retarding heat transfer. Therefore, a fire in one room, which is separated from an adjacent room by a fire-resistance rated drywall assembly, will not cause this adjacent room to get any warmer than the boiling point (100°C) until the water in the gypsum is gone. This makes drywall an ablative material because as the hydrates sublime, a crumbly dust is left behind, which, along with the paper, is sacrificial. Generally, by increasing the layers of Type X drywall, the more one increases the fire-resistance of the assembly, be it horizontal, or vertical. Evidence of this can be found both in publicly available design catalogues on the topic, as well as common certification listings. "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 and ceilings 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.

Mechanical shaft with compromised fire-resistance rating through pipe installation.

Fire testing of drywall assemblies for the purpose of expanding national catalogues, such as the Canadian National Building Code, 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. In this case, the code design becomes the basis for bounding. For the purpose of unique designs, certified by organisations holding national accreditation for testing and certification such as Underwriters Laboratories, only the test sponsor's material qualifies for use in field bounding. 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 right here. 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 occurr 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.

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.^[2] Moreover, the home building and remodeling markets in North America have increased demand the 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."^[3]

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.^[4] 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.

Waste

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 may 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.

Types available in the USA and Canada

• Regular white board, from 1/4" to 3/4" thickness
• Fire-resistant ("Type X"), different thickness and multiple layers of wallboard provide increased fire rating based on the time a specific wall assembly 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 in the green colored paper covering that provides moisture resistance. It is commonly used in washrooms and other areas expected to experience elevated levels of humidity.
• Blueboard or gypsum base, the blue face paper forms a stong bond with a skim coat or a built-up plaster finish
• Concrete backerboard, sometimes known as Durock, which is more water-resistant than greenboard, for use in showers or sauna rooms, and as a base for ceramic tile
• Soundboard is made from wood fibers or other dampening materials to increase the sound rating (STC)
• Mold-resistant, paperless drywall from Georgia-Pacific
• Enviroboard, a board made from recycled agricultural materials
• Lead-lined drywall, a drywall used around radiological equipment
• Foil-backed drywall to control moisture in a building or room

Common drywall tools

• Corner trowels
• Dimpler
• Drywall screws and nails
• Drywall Jack
• Electric screwdriver
• Joint compound and Ready-mix lightweight joint compound
• Keyhole saw or drywall router
• Taping/joint knives
• Utility knife
• Surform

See also

• Ablation
• Bounding
• Cement board
• Certification mark
• Compartmentalization
• Construction
• Endothermic
• Fire protection
• Firestop
• Firewall (construction)
• Gypsum
• Product certification
• United States Gypsum

References

Wikipedia information about Drywall This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Drywall". It may not have been reviewed by professional editors (see full disclaimer). Help contribute to Americola and edit this article.