A �”-thick sheet material of concrete and fiberglass used as underlayment in showers, on countertops, and other places where a moisture barrier is desired. The sheets are installed in much the same manner as gypsum drywall. The 3’x5’ sheets are cut to size and fastened to the structural backing, such as the cabinet base or wall studs, using drywall screws. Joints between panels are sealed with drywall joint tape and thinset mortar or whatever adhesive is to be used to set the tile. The surface covering is then applied according to manufacturer’s instructions.