Sheetrock is the brand name for the drywall produced by the United States Gypsum Company, and while it's common, it isn't the only type of drywall around. Drywall consists of a paper-covered, hard-packed gypsum core, and it usually comes in 4- by 8-foot sheets with thicknesses from 1/4 to 5/8 inches. It's one of the most common waste materials produced on construction sites, and it's important to dispose of it responsibly.
Its Gypsum Composition
The original drywall, Sheetrock consists of 90 percent gypsum and 10 percent paper. Gypsum is a naturally occurring mineral known as hydrous calcium sulfate, which is a mixture of calcium sulfate and water. The gypsum used to make drywall is mined from ancient seabeds, where it collected over eons. The plaster used to coat drywall, which must often be discarded at the same time as the drywall itself and is often referred to as mud, is 100 percent gypsum. Gypsum is hard and powdery when dry, but it turns into a slurry when mixed with water.
Drywall as Landfill
Many builders simply bag up the drywall left over from a construction project and throw it in the landfill, but there's a problem with this approach. Although neither gypsum nor paper are toxic, the materials can provide a substrate for microorganisms to grow. When organic matter is added to the landfill, these organisms convert the sulfate in gypsum to hydrogen sulfide, a foul-smelling gas. The resulting odor problem can be so severe that some communities ban the disposal of drywall in landfills. Gypsum from discarded drywall can also leach into the soil during heavy rains and contaminate the groundwater.
Many communities recycle the gypsum in drywall to use as a soil conditioner, with facilities at landfill stations to handle this recycling. Among the many ways it benefits soil, gypsum replaces sodium, making the soil less salty, and it provides a source of calcium and sulfur without raising pH. It also helps loosen compacted soil. Drywall castoffs from new construction are the easiest to recycle; when recycling drywall from remodeling projects, it's necessary to remove nails and pieces of wood trim first. Drywall from older houses may have been painted with lead-based paint, and because lead is toxic, this drywall should not be recycled.
The best drywall disposal solution is to avoid creating waste in the first place. One way to minimize waste is to order sheets with dimensions appropriate for the room you're drywalling and to cut judiciously. Scrap pieces of drywall also come in handy as concrete forms. If you're engaged in new construction, Cal Recycle recommends placing scrap pieces of drywall in the wall cavities before you cover them. You can also save drywall pieces for another project, offer them for free online as salvage or donate them to the project of another builder or organization, such as Habitat for Humanity.