Drywall
[2] The plaster is mixed with fiber (typically paper, glass wool, or a combination of these materials); plasticizer, foaming agent; and additives that can reduce mildew, flammability, and water absorption.
In 1910 United States Gypsum Corporation bought Sackett Plaster Board Company and by 1917 introduced Sheetrock.
Later air entrainment technology made boards lighter and less brittle, and joint treatment materials and systems also evolved.
[8] In 1936, US Gypsum trademarked ROCKLATH[9] for their gypsum lath product.In 2002, the European Commission imposed fines totaling €420 million on the companies Lafarge, BPB, Knauf and Gyproc Benelux, which had operated a cartel on the market which affected 80% of consumers in France, the UK, Germany and the Benelux countries.
The raw gypsum, CaSO4·2H2O, is heated to drive off the water and then slightly rehydrated to produce the hemihydrate of calcium sulfate (CaSO4·1/2H2O).
The plaster is mixed with fiber (typically paper and/or glass fiber), plasticizer, foaming agent, finely ground gypsum crystal as an accelerator, EDTA, starch or other chelate as a retarder, and various additives that may increase mildew and fire resistance, lower water absorption (wax emulsion or silanes), reduce creep (tartaric or boric acid).
[11] The board is then formed by sandwiching a core of the wet mixture between two sheets of heavy paper or fiberglass mats.
The sulfur is absorbed by powdered limestone in a process called flue-gas desulfurization (FGD), which produces several new substances.
Small features such as holes for outlets and light switches are usually cut using a keyhole saw, oscillating multi-tool or a tiny high-speed bit in a rotary tool.
Their function saves material and labor costs, minimizes call-backs due to truss uplift, increases energy efficiency, and makes plumbing and electrical installation simpler.
Veneering uses a slightly different specialized setting compound ("finish plaster") that contains gypsum and lime putty.
[20] Drywall is highly vulnerable to moisture due to the inherent properties of the materials that constitute it: gypsum, paper, and organic additives and binders.
Gypsum will soften with exposure to moisture and eventually turn into a gooey paste with prolonged immersion, such as during a flood.
The porosity of the board—introduced during manufacturing to reduce the board's weight, lowering construction time and transportation costs—enables water to rapidly reach the core through capillary action, where mold can grow inside.
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.
They use rapid drying techniques that eliminate the elements required to support microbial activity while restoring most or all of the drywall.
However, individual manufacturers may also have proprietary designs that they have had third-party tested and approved, provided that the material used in the field configuration can be demonstrated to meet the minimum requirements of Type X drywall and that sufficient layers and thicknesses are used.
These fibers reduce the size of the cracks that form as the water is driven off, thereby extending the length of time the gypsum panels resist fire without failure.
The core of Type C panels also contains vermiculite which acts as a shrinkage-compensating additive that expands when exposed to elevated temperatures of a fire.
There is potential for using crushed drywall to amend certain soils at building sites, such as sodic clay and silt mixtures (bay mud), as well as using it in compost.
"[27] The introduction in March 2005 of the Clean Air Interstate Rule by the United States Environmental Protection Agency requires fossil-fuel power plants to "cut sulfur dioxide emissions by 73%" by 2018.
[28] 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.
[29] 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.
Volatile sulfur compounds, including hydrogen sulfide, have been detected as emissions from the imported drywall and may be linked to health problems.
Several lawsuits are underway in many jurisdictions, but many of the sheets of drywall are simply marked "Made in China", thus making the manufacturer's identification difficult.
[citation needed] Drywall panels in Canada and the United States are made in widths of 48, 54, and 96 inches (1.2, 1.4, and 2.4 m) and varying lengths to suit the application.
