Though drywall long ago overtook plaster as the dominant finishing material for interior walls, you may be unsure of what drywall is exactly or what it is made from. The outside of a sheet of drywall is a kind of paper, but the interior sandwiched between the paper pieces is a mixture of minerals, water, starch-based glue, asphalt-based wax emulsions and paper pulp as well as chemicals to reduce flammability or prevent molding. The exact mix depends upon what kind of drywall you purchase. Though there are variations, all drywall is made up of one main mineral.
While there are a number of substances in drywall, most are not minerals. The major mineral component in all drywall is gypsum, chemically known as calcium sulfate dihydrate. This simply means that gypsum is formed from calcium, a sulfur compound and water. In its natural form, gypsum is white in color. It has several uses in construction and in general use, and for drywall, some of its major virtues are that it's noncombustable, does not react significantly with many materials and has very low toxicity.
While gypsum is found naturally in the ground, it can also be made by humans. When power plants burn coal, this produces a number of byproducts and gases, including sulfur dioxide. This sulfur dioxide is reacted with a limestone slurry. Limestone is made from calcium carbonate. The reaction between the limestone and sulfur dioxide gas creates calcium sulfate instead, or gypsum, making what would be an undesirable gas into a mineral that is used in drywall. This process is known as flue gas desulfurization, or FGD gypsum.
Boron is a mineral as well as an element. Found naturally in a number of different compounds, the mineral forms very hard, transparent crystals. One of its compounds, boron carbide, forms crystals that only diamond rivals in hardness, and it can be used as a very effective abrasive. In drywall, however, boron is often added to the gypsum to serve as a fire retardant. Boron does not add to the toxicity of drywall and is in fact a mineral essential to plant health in particular.
Though drywall's major mineral is gypsum, the gypsum can contain impurities depending upon where it was mined, if it was mined and not created chemically by humans. This may include other calcium compounds, like calcium carbonate or calcium hydroxide, as well as quartz, which is made from silicon and oxygen. Trace metals may also be present, such as copper, zinc or manganese. Some of these trace metals may be toxic, such as mercury or lead, but the acceptable levels present in drywall are regulated.
- Glenn Construction: Green Board Drywall & Cement Board
- Centers for Disease Control and Prevention: Gypsum
- National Gypsum: What is FGD Gypsum?
- Florida Department of Environmental Protection: Innovative Drywall Recycling Grant
- CalRecycle: Wallboard (Drywall) Recycling
- Georgia State University: Boron
- Nature's Way Resources: Gypsum (CaSO4)
- U.S. Green Guilding Council's Green Home Guide: Is There Such a Thing as Green Drywall?
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