At the latest conference, the program focused on waterproofing materials. The number of contractors attending the conference who believed—in spite of manufacturer specifications and recommendations to the contrary—that cement backerboards, latex thinset mortar, and latex grout could all be relied on to provide complete waterproofing for tiles installed in wet areas, was amazing. And at a time when more states are holding contractors liable for longer periods of time (longer than the traditional one year), more failures are being reported, especially in wet-area installations. But it’s not that installers are using the wrong products; it’s that they are installing them incorrectly.
For wall installations, the minimum acceptable membrane recognized by the tile industry is a layer of 15-pound, tar-saturated, felt paper, or a sheet of 4-mil plastic film positioned behind cement backerboards. However, there are a couple of reasons why this kind of membrane cannot be relied upon for some wet area installations that get plenty of use. The first is that when the backerboards are installed, the nail- or screw-fasteners puncture the membrane. The second is that when the joint below the first course of tiles is filled with a resilient caulk—on a tub surround, for example—the caulk often seals the membrane to the tub, and acts like a dam, trapping the water that penetrates the tiles and grout. This water can seep through the fastener penetrations and damage the wood structure supporting the tiles. A much better approach is to install a surface-applied membrane to the surface of the backerboards before the tiles are installed.
For floor installations, many contractors install cement backerboards without a membrane, and a few will omit the bedding layer of thinset mortar. Installing backerboards without the bedding layer almost guarantees that there will be water damage to the structure, even if a surface-applied membrane is installed. To assure that moisture is not a problem, the backerboards must be installed properly, and a waterproofing membrane must also be applied to the surface of the boards prior to the installation of the tile.
Floor covering installers who have installed sheet goods directly over wooden underlayments in bathrooms and other wet area floors—and who have sealed the edges of such floors with a resilient caulk—do not have to worry too much about water penetration, as long as the sealant remains intact and the sheet goods are kept in good condition, with no rips or tears.
Unfortunately, some installers use the same ¼- or ⅜-inch wood panels they use for sheet goods as underlayments for ceramic tile installation. The results are often disastrous, as these thin wood panels are not recommended for use with ceramic tile; movement in the underlayment that does not affect flexible sheet goods can quickly damage rigid ceramic tiles. In addition, intact sheet goods act like waterproofing membranes, helping to protect the underlayment, while tiles, grout, and thinset may allow the passage of moisture, which can damage wooden underlayments. However, covering a ½-inch, exterior-grade plywood underlayment with a waterproofing membrane can result in a watertight ceramic tile floor capable of supporting a greater load than a plywood subfloor covered with a cement backerboard.
Finally, to assure that the waterproofing membrane and the tile perform as expected for the life of the installation, all ceramic floor tile installations need to be surrounded with a perimeter expansion joint. The term expansion joint can mean different things to different installers, so to avoid confusion: expansion joints for tile are grout joints filled with a resilient material instead of hard grout. Without appropriate expansion joints, membranes can crack or leak, and tiles can shear off the surface from normal movement in a structure. Expansion joints could easily be the subject of many articles, so I encourage all ceramic tile installers to refer to EJ 171 in the Tile Council of America Handbook (TCA 1-864-646-8453).
Waterproofing membranes should not scare you away from installing ceramic tiles. They are a key to both increased profitability and reduced liability.