plasterboard

Example of drywall with joint compound, the common interior building material. (This photo shows drywall hung vertically.)

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Drywall is the term used for a common method of constructing interior walls and ceilings using panels made of gypsum plaster pressed between two thick sheets of paper, then kiln dried. Drywall construction is used globally for the finish construction of interior walls and ceilings. Drywall construction became prevalent as a speedier alternative to traditional plaster interior finish techniques, which involved hand-placing base, scratch and finish coats in successive layers by hand. (See also, the history of Homasote, a dry applied wall or ceiling board finish system.) Drywall, by contrast, required hand finishing only at the fasteners and joints. The new process required less labor and drying time, lending its name to the panels used in the assembly.^{[citation needed]}

Panels installed may be known as gypsum board, wallboard, plasterboard (USA, UK, Ireland, Spain, Australia), Gibraltar board or gib wall and ceiling linings (in New Zealand trademark of Winstone Wallboards), rock lath^[1], Sheetrock (a trademark of USG Corporation, rigips (Germany and Central Europe - after the Rigips brand), alçıpan in Turkey, and placoplatre (France).

History

“Sackett Board” was invented in 1894 by Augustine Sackett. It was made by layering plaster within four plies of wool felt paper. Sheets were 36" x 36" x 1/4" thick with open (untaped) edges."^[2]

"Gypsum Board" evolved between 1910 and 1930 beginning with wrapped board edges, and elimination of the two inner layers of felt paper in favor of paper-based facings. Later "air-entrainment technology" made boards lighter and less brittle, then joint treatment materials and systems also evolved. "^[2]

"Rock 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.^[1]

Manufacture

A wallboard 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, CaSO₄·2 H₂O, (mined or obtained from flue gas desulfurization (FGD)) must be calcined before use. Kettle or Flash calciners typically use natural gas today. The plaster is mixed with fiber (typically paper and/or fiberglass), plasticizer, foaming agent, finely ground gypsum crystal as an accelerator, EDTA, starch or other chelate as a retarder, various additives that increase mildew and fire resistance (fiberglass or vermiculite), wax emulsion for lower water absorption 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. ^[3].

Drying chambers typically use natural gas today. To dry 1 MSF (1,000 square feet) of wallboard, between 1.75-2.49 million BTU is required. This is the main reason why organic dispersants/plasticisers are used i.e. to reduce the amount of water to produce gypsum slurry flow during wallboard manufacture.^{[4][unreliable source?]}

Specifications

USA and Canada

Drywall panels are manufactured in 48 inches (120 cm) wide panels in varying lengths to suit the application. Common panel thicknesses are 1/2" and 5/8", with panels also available in 1/4" and 3/8". 5/8" panels are used where a fire-resistance rating is desired or where additional mass is needed for the reduction of sound transmission.^{[citation needed]}

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.^{[citation needed]}

Europe

In the UK and Europe, plasterboard is manufactured in metric sizes, with the common sizes being corollaries of old imperial sizes.

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.

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.^{[citation needed]}

Plasterboard is commonly made with one of two 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, and straight edge, where edge thickness is the same as the middle of the board.

Construction techniques

Drywall is delivered to a building site on a flatbed truck and unloaded with a forked material handler crane. The bulk drywall sheets are unloaded directly to upper floors via a window or exterior doorway.

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.^{[citation needed]}

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, glue, 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 labour expenses; to minimise call backs due to truss uplift; to increase energy efficiency; and to make plumbing and electrical installation simpler.

Drywall screws are designed to be self-tapping.

Drywall screws heads have a curved taper 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.

Electric screw gun used to drive drywall screws

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 minimise 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 specialised 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 resistance

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 vapourised, retarding heat transfer. Therefore, a fire in one room that 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, the more layers of Type X drywall one adds, 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, including, but not limited to DIN4102 Part 4 and the Canadian Building Code on the topic, as well as common certification listings, including but not limited to certification listings provided by Underwriters Laboratories and Underwriters Laboratories of Canada (ULC). "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, 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.
Finished, painted, fire-resistance rated drywall assembly. A common deficiency: Lift ceiling tiles and find electrical and mechanical service penetrations without a firestop.	Improper drywall and absent firestops	Improper Firestop and Fireproofing interface, August 2000	Improper breach of fire-resistance rated drywall assembly, August 2000
The "I-was-there-first" scenario, resulting in improper drywall firestops with plastic piping.

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.^[5] 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, 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, which is independent of the assemblies penetrated, can be separately arranged.

North American market

North America is one of the largest gypsum board users in the world with a total wallboard plant capacity of 42 billion square feet per year (world wide 85 billion square feet per year).^[6] 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."^[7]

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.^[8] 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. ^[9]

Waste

Because up to 17% of drywall is wasted during the manufacturing and installation processes^{[citation needed]} and the drywall material is frequently not re-used, disposal can become a problem. Some landfill sites have banned the dumping of drywall. Some manufacturers take back waste wallboard from construction sites and recycle it into new wallboard. Recycled paper is typically used during manufacturing. More recently, recycling at the construction site itself is being investigated. There is potential for using crushed drywall to amend certain soils at building sites, such as clay and silt mixtures (bay mud), as well as using it in compost.^[10]

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, the 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.^{[citation needed]}
• Blueboard, blue face paper forms a strong bond with a skim coat or a built-up plaster finish providing both water and mold resistance.
• Cement board, 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 to increase the sound rating (STC)
• Soundproof drywall is a laminated drywall made with gypsum, other materials, and damping polymers to significantly increase the STC^{[citation needed]}
• Mold-resistant, paperless drywall^{[citation needed]}
• Enviroboard, a board made from recycled agricultural materials
• Lead-lined drywall, a drywall used around radiological equipment^{[citation needed]}
• Foil-backed drywall to control moisture in a building or room^{[citation needed]}
• Controlled density (CD), also called ceiling board, which is available only in 1/2" thickness and is significantly stiffer than regular white board

Common drywall tools

Levels of finish

"In 1990, four major trade associations, the Association of Wall and Ceiling Industries International (AWCI), the Ceilings and Interior Systems Construction Association (CISCA), the Gypsum Association (GA), and the Painting and Decorating Contractors of America (PDCA), presented the consensus document Levels of Gypsum Board Finish. The document was created to "precisely describe" the desired finish of walls and ceilings prior to final decoration. This precise description enables contractors to better understand the requirements of architects and building owners in order to enhance the satisfaction of the client. Specifications that include the Levels of Gypsum Board Finish also promote competitive bidding that allows the bidder to consider the correct labor and materials to finish the wall suitably for its final decoration." [1]

The official document (summarized below) is known as GA-214-96 "Recommended Levels of Gypsum Board Finish".

Level 0

No taping, finishing, or accessories required.

Usage: Temporary construction or when final decoration is undetermined.

Level 1

All joints and interior angles shall have tape set in joint compound. Surface shall be free of excess joint compound. Tool marks and ridges are acceptable.

Usage: Above false ceilings or other areas which are out of public view where a degree of fire and noise resistance is required.

Level 2

All joints and interior angles shall have tape embedded in joint compound and wiped with a joint knife leaving a thin coating of joint compound over all joints and interior angles. Fastener heads and accessories shall be covered with a coat of joint compound. Surface shall be free of excess joint compound. Tool marks and ridges are acceptable. Joint compound applied over the body of the tape at the time of tape embedment shall be considered a separate coat of joint compound and shall satisfy the conditions of this level.

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.

Level 3

All joints and interior angles shall have tape embedded in joint compound and one additional coat of joint compound applied over all joints and interior angles. Fastener heads and accessories shall be covered with two separate coats of joint compound. All joint compound shall be smooth and free of tool marks and ridges. It is recommended that the prepared surface be coated with a drywall primer prior to the application of final finishes.

Usage: Suitable base for heavy-medium textured paint or other thick finishes.

Level 4

All joints and interior angles shall have tape embedded in joint compound and two separate coats of joint compound applied over all flat joints and one separate coat of joint compound applied over interior angles. Fastener heads and accessories shall be covered with three separate coats of joint compound. All joint compound shall be smooth and free of tool marks and ridges. It is recommended that the prepared surface be coated with a drywall primer prior to the application of final 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.

Level 5

All joints and interior angles shall have tape embedded in joint compound and two separate coats of joint compound applied over all flat joints and one separate coat of joint compound applied over interior angles. Fastener heads and accessories shall be covered with three separate coats of joint compound. A thin skim coat of joint compound, or a material manufactured especially for this purpose, shall be applied to the entire surface. The surface shall be smooth and free of tool marks and ridges. It is recommended that the prepared surface be coated with a drywall primer prior to the application of finish paint. 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.

Usage: Gloss and entirely non-textured surfaces.

Defective Chinese imports

There are reports that a substantial amount of defective drywall was imported into the United States from China and incorporated into tens of thousands of homes during rebuilding in 2006 and 2007 following Hurricane Katrina and in other places. Complaints include foul odor, health effects, and corrosion of metal within the structure. The same drywall was sold in Asia without problems resulting, but US homes are much tighter than Asian homes. A number of lawsuits are underway in many jurisdictions, but many of the sheets of drywall are simply marked, "Made in China", thus making identification of the Chinese manufacturer difficult. An investigation by the Consumer Product Safety Commission was underway in 2009.^[11]

See also

References

External links

Wikimedia Commons has media related to: Drywall

• Gypsum Association is an organization owned by several manufacturers of gypsum board in the US and Canada