A backer board designed for use in wet areas such as showers. Because cement is not harmed by water, cement board will not deteriorate when water gets through the grout. While there is no doubt that the gypsum based products are the easier to work with and less expensive, you will pay a price for this convenience. The price will be a complete new tile and backer board installation job within 7 - 10 years. If you follow the instructions provided by the manufacturers and the Tile Council of America, you very likely will have a permanent ceramic tile installation.