Drywall

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

Drywall, Plasterboard or also called gypsum board are panels made of gypsum plaster pressed between two thick sheets of paper, the panels are used to make interior walls and ceilings.

Plasterboard panels are also known as wallboard^{[citation needed]} (USA, UK, Ireland, Australia), Gibraltar board or GIB wall and ceiling linings (in New Zealand, trademark of Winstone Wallboards^[1]), rock lath,^[2] Sheetrock (a trademark of USG Corporation), Gyproc (a trademark of Compagnie de Saint-Gobain).

The sheets of the drywall can be made from fiberglass instead of paper to prevent mold growth. Mold growth is common when using paper based plasterboard that has been exposed to water due to plumbing leaks or floods.

Drywall construction became prevalent as a speedier alternative to using plaster based interior finish techniques, which involved forcefully spreading a substrate of coarse plaster, known as the base (made up of the scratch coat and (optional) brown coat), onto the wall’s lath-work before finally applying the smoother finish coat, each layer added in succession and all by hand (see lath and plaster).^[3] Drywall, by contrast to plaster, requires hand finishing only at the fasteners and joints. The drywall process requires less labor and drying time, lending its name to the panels used in the assembly.^{[citation needed]}

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.”^[4]

“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. “^[4]

“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.^[2]

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 may increase mildew and/or fire resistance (fiberglass or vermiculite), wax emulsion or silanes 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.

Drying chambers typically use natural gas today. To dry 1 MSF (1,000 square feet) of wallboard, between 1.75 and 2.49 million BTU is required. Organic dispersants/plasticisers are used mainly to reduce the amount of water, hence reduce the eventual drying time, needed to produce gypsum slurry flow during wallboard manufacture.^[5]

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″ (13 mm) and 5/8″ (16 mm), with panels also available in 1/4″ (6 mm) and 3/8″ (10 mm). Both 1/2″ (13 mm) and 5/8″ (16 mm) panels of TYPE ‘X’ (a gypsum board with special core additives to increase the natural fire resistance of regular gypsum board^[6]) are used where a fire-resistance rating is desired. Regular 5/8″ (16 mm) panels are used (with or without light gauge resilient metal channels) where additional mass is needed for the reduction of sound transmission.^{[citation needed]}

Drywall provides a thermal resistance R-value of 0.32 for 3/8″ board, 0.45 for 1/2″, 0.56 for 5/8″, and 0.83 for 1″ 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 120 cm wide sheets, though 90 cm wide sheets are also made. 120 cm wide plasterboard is most commonly made in 240 cm lengths, though 270 cm and 300 cm 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 plain edge, used where the whole surface will receive a thin coating (skim coat) of finishing plaster.

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 minimize 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 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.

Water damage and mold

Drywall water damage in a closet.

Drywall is easily damaged by exposure to water. While it can be waterproofed through covalent waterproofing, if waterproofing is absent or if the waterproofing layer is punctured, water will cause drywall to swell and eventually disintegrate, requiring replacement. Drywall is a porous, lightweight substance that supports the growth of mold. It is for this reason that greenboard and cement board is used for rooms expected to have high humidity.

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.