Gypsum concrete

[6] US patent 4,444,925 lists the components of Gyp-Crete as atmospheric calcined gypsum, sand, water, and small amounts of various additives.

Additives listed include polyvinyl alcohol, an extender such as sodium citrate or fly ash, a surfactant such as Colloid defoamer 1513 DD made by Colloids, Inc., and a fluidizer based on sodium or potassium derivatives of naphthalene sulfonate formaldehyde condensate.

While the exact mechanism is not known, it is thought that as the concrete sets, water migrates to the surface, bringing with it fine, dusty particles.

Once all the sand and calcined gypsum have been mixed in, the rest of the water is added until the proper consistency is attained.

Finally, the additives are mixed in and the whole batch of concrete is moved to the holding tank to be pumped out into the required area via long hoses.

It was stated that gypsum calcined at atmospheric pressure produced poor results due to it having flaky particles, and that gypsum calcined under a pressure of 15-17 psi produced better results because it had denser, crystalline particles.

The latex emulsion and antifoaming agent were no longer necessary as the concrete was strengthened by the Portland cement.

[13] In the late 1940s, copper tubing and Portland concrete were used to install radiant heat flooring.

However, this practice fell out of use in the United States within 15–20 years because the Portland concrete was too corrosive on the copper tubing.

In the 1980s gypsum concrete again became widely used in the United States for radiant heat flooring as cross-linked polyethylene (PEX) tubing could be used with gypsum concrete for radiant heat flooring without concern for corrosion on the PEX tubing.