When Pat went to put ceramic tile on his shower stall Mike told him to be sure to use green backer board. This is a mistake that many make because green backer board, although water-resistant, is not (unfortunately) waterproof. What Pat really needed was concrete backer board, which combines both cement and a fiberglass mat. This protects much like a traditional metal lath and Portland cement undercoat. In green board, the center core of gypsum is treated with chemicals making it only water-resistant, and the paper color notes it is for use in high- moisture areas (such as on bathroom walls and ceilings). For true waterproofing in extremely wet areas, Mike should first install a "barrier" material over the studs such as black roofing felt. Then install concrete backer board (also called cementitious backer unit or CBU), and shower tile will stay on walls for many years. And that's the On The House tip for today.