While watching Ask This Old House today, the show included Richard Trethewey applying thinset to the cement board surface then he applied a waterproof polyester membrane fabric that is used to waterproof the walls of the shower stall. Who makes this material and where can I get it locally? I live in the Los Angeles area and would like to get it for the tile work I will do tomorrow. Maybe Lowes or Home Depot carry it, but when I went to both today, each said they didn't know if they carried it or not. I appreciate any help.