Gypsum concrete underlayment is a mixture of gypsum, Portland cement and sand supplied in bag form. Typically, it is mixed with water, and pumped or poured while in a liquid state over suitable substrates. The underlayment mix then is poured over a structurally sound concrete or precast floor at a minimum depth of 1/2 inch, or a depth of 3/4 of an inch over a structurally sound wood subfloor.
At this point in time, there are approximately 150 certified applicators in the field. The primary reasons for using gypsum underlayment are to meet accepted sound and fire ratings, and to provide a suitable surface for the installation of flooring.