When we ask who has the last word in the use of tile-related products or procedures, we need to begin with a firm foundation. The TCNA Handbook and American National Standards Institute (ANSI) specifications are the foundation or the starting point when we look at the how and/or why of properly installed tile.
The Industry Standards and Details: As an example, we will look at the requirements of a shower receptor installation as found in the Handbook detail B415. Under the Membrane Options section it states: “A waterproof membrane (A118.10) or vapor retarder membrane (A108.02-3.8) must be specified for walls to prevent moisture intrusion and protect adjacent building materials. Specifier shall indicate if complete waterproofing of walls is required, including treatment at termination points.”
The critical word in this statement is just two letters “or” as highlighted in the quoted text. This means that the installer installs either a waterproof membrane on the surface of the backer board or a vapor retarder membrane on the studs prior to installing the backer board, not both. Never install vapor retarder membrane and a topically applied waterproof membrane on a shower wall. The reason for this is that moisture can be trapped between them with no way to be released.
Detail B415 utilizes either Cement Backer Board or Fiber-Cement Backer Board on the walls, but other Handbook wall details include a Mortar Bed, Coated Glass Mat Water-Resistant Gypsum Backer Board, Cementitious-Coated Extruded Foam Backer Board, Fiber-Reinforced Water-Resistant Gypsum Backer Board, or a Bonded Waterproof Membrane. They are all installed differently, so follow the written instructions.
The Manufacturer’s Directions: It can’t be stressed strongly enough that the installer must follow the written instructions of the manufacturer of the products being installed. Always carefully read and follow the provided directions since product installation methods may vary from one manufacturer to another. Don’t assume that all backer boards are installed exactly the same way. Also, when possible, use one manufacturer’s products or system. Most times the installed system includes the manufacturer’s warranty.
The Local Building Code: We have seen that the Handbook and ANSI instruct the installer how to install the specified products and that the product manufacturer has specific instructions for its products. However, the final use and installation of products in the tile assembly is controlled by the local building code. The local building code has the final word on what products are required and what products may or may not be used in that particular city, township, county, or parish. Always check the code in the area where the work is being done, since the code can and does vary from one place to another.
Be careful! You may be required to tear out what has been installed if it does not meet the local code.