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Q.My excavation contractor offered to bury my scrap drywall on site, but I've heard buried gypsum can create a harmful gas. I've also read that it's okay to bury small amounts if you disperse it. Is it okay to bury drywall on site at all, and if so, what's the proper way to do it?

A.Alex Wilson, editor of Environmental Building News in Brattleboro, Vt., responds: You're right that it's not a good idea to simply bury scrap drywall in a hole. Under oxygen-depleted conditions, such as in a landfill or several feet underground in a covered hole, the gypsum (calcium sulfate) in drywall can decompose to release the noxious gas hydrogen sulfide. This gas is hazardous at high concentrations and an odor problem even at very low levels. Problems have sometimes arisen when builders have buried the scrap drywall from a house. The rotten egg smell is not at all popular with homeowners.

However, scrap drywall can safely be used as a soil amendment in the oxygen-rich, active top few inches of soil if it is properly pulverized and applied. Drywall is composed of paper facings and gypsum. Gypsum is often used as a fertilizer, adding both calcium and sulfur. Along with the benefits of the gypsum, the unbleached paper adds tilth to soil. The following recommendations should help you avoid problems and use drywall scrap properly as a soil amendment:

  • Only new (unpainted) drywall scrap should be used as a soil amendment.
  • The drywall should be pulverized to allow rapid disintegration; no pieces should be larger than 1/2 inch in diameter. Some builders have used a brush chipper successfully to pulverize the drywall (wear a dust mask!).
  • Pulverized drywall can be spread on the soil surface or tilled into the top layer of soil (no more than a few inches deep).
  • The pulverized drywall should be spread evenly over the entire lot or area being seeded.
  • Pulverized gypsum may be added at rates of up to 1 pound per square foot (22 tons per acre), though spreading it much more thinly is generally recommended. Gypsum's effect on soil quality varies depending on the type of soil, so it's best to ask your county agricultural extension agent for guidance on how much added gypsum is appropriate for your local soil.
  • Pulverized drywall should be applied to soil only in areas with adequate drainage and aeration (no standing water or anaerobic conditions).
  • Finally, you should find out if there are specific regulations in your area that address the disposal of drywall scrap in this manner, or if any permit is required for this practice.

For more on the use of drywall scrap as a soil amendment, visit the Gypsum Association website: http://www.gypsum.org/topical.html.