In the late 1940s, copper tubing and Portland concrete were used to install radiant heat flooring. The copper tubes would be laid out around the ground and then the Portland concrete could be poured to cover the tubing and make an even base for the floor. 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 plastic PEX tubing could be used with Gypsum concrete for radiant heat flooring without concern for corrosion on the PEX tubing. Notes 1. The table in the patent lists the PVA content as 0.45 grains (0.00002%). Later on, it is stated that the PVA should be in a 1:0.005625 ratio with the calcined gypsum. This yields a PVA content of 0.45 lbs (0.16%). References Concrete Soil-based building materials