In this article, you'll learn...

  • What additional measures to take when installing tile in a wet environment 
  • What is Res2 (Residential Limited Water Exposure)
  • What is Res3 (Residential Wet)

The beauty, functionality, durability and longevity of ceramic tile are all for naught if the location of the installation is not properly considered. Wet areas present significant challenges that must be addressed prior to the start of the installation to ensure that the properties mentioned above are provided.

To understand tile installation in wet areas, we first need to define the subject. The TCNA Handbook supplies these definitions in the Environmental Classifications section. There are also very similar statements for commercial applications when applicable. 

  • Res2 (Residential Limited Water Exposure): Tile surfaces that are subjected to moisture or liquids but do not become soaked or saturated due to the system design or time exposure. If waterproofing is desired, it must be clearly specified and includes areas adjacent to R3 areas. Examples: Floors in bathrooms, kitchens, mudrooms, laundry and foyers, where water exposure is limited and/or water is removed; some backsplashes, some wainscots, some countertops.
  • Res3 (Residential Wet): Tile surfaces that are soaked, saturated or regularly and frequently subjected to moisture or liquids. Examples: Shower floor; floors and other horizontal surfaces where water is not removed or drained, such as some countertops; tub wall, shower walls and enclosed pool area walls.

Since we know that the tile itself does not create a waterproof environment, additional measures need to be taken as part of the installation process. For the most part, the tile surface, either glazed or unglazed, does repel water, but other than a porcelain product, the body of the tile is absorptive to some degree. The only way to stop the movement of the water absorbed through the grout joints and into the tile body is to provide a positive water barrier behind the tile, while also providing a load-bearing capacity.

The application of a waterproof membrane is an excellent way to segregate the water from the substrate. These products come in three basic categories — liquid, trowel-applied and sheet — and they are designed to accomplish three objectives. The first is to bond tenaciously to the surface, which is being protected. Second, the membrane must allow the mortar or adhesive to bond adequately in order to support the weight of the tile products being installed. And third, it needs to prevent the water from entering the substrate efficiently and effectively.

The liquid- and trowel-applied products range in consistency from a cream to a thick paste and are applied over a number of manufacturer approved surfaces. They are designed to be applied by using a brush, a heavy-napped roller or a trowel meeting the required thickness. Many of these products require two or more coats with a specified dry time in between coats. The use of a wet film thickness gauge is an excellent way of obtaining the desired thickness.

Sheet waterproofing membranes are available in a number of widths, thicknesses and compositions. Depending on the manufacturer, they range in size from 1 meter (39.37 inches) up to 1.524 meters (60 inches) and vary from 8 to 40 mm thick. The product composition may be chlorinated polyethylene (CPE), polyethylene or polyvinyl chloride (PVC), which is covered on both sides with a fleece webbing or scrim that allows it to be bonded with a specified thin-set mortar or adhesive. The key here is to contact the manufacturer for their written instructions, which must be followed implicitly. Combining products and/or methods from various suppliers is a recipe for failure.

An additional product is also included in this grouping. Uncoupling membranes, which are designed to allow independent movement between the floor tile and the substrate and limit the transfer of stresses, can also provide a waterproofing capacity if the product joints and wall connections are installed according to the manufacturer’s recommendations.

Almost all of the methods contained in the 2013 TCNA Handbook provide a section entitled “Membrane Options.” For example, under Shower Receptors, method B415 states the following:

  • A waterproof membrane (A118.10) may be specified to prevent moisture intrusion and protect adjacent walls and building materials. Specifier shall indicate if complete waterproofing of walls is required, including treatment at termination points.
  • Check with membrane manufacturer for suitability for applicable conditions, as not all membranes are suitable for stream, high-temperature and/or chemical exposure or exterior use.
  • When glass tile is used, consult glass tile manufacturer for membrane options and recommendations.

As you can see, not all products will function effectively in all applications. The manufacturer’s guidelines should be part of the planning process in order to deliver the desired result.

Many of these products call for a thin-set mortar to be used to either bond the sheet membranes to the substrate or to bond the tile to the membrane. Depending on the manufacturer, it may be a Dry-Set Cement Mortar (A118.1), a Modified Dry-Set Mortar (A118.4), an EGP (Exterior Glue Plywood) Latex-Portland Cement Mortar (A118.11) or the latest addition to this category, an Improved Modified Dry-Set Cement Mortar (A118.15). This may sound like a broken record, but consult the manufacturer for specific instructions since one size does not fit all.

There is one additional aspect of these mortars which is critical in wet areas. Is the mortar recommended to be used in wet interior areas or outside? This may sound odd, but some mortars are not to be used in wet areas due to the latex composition used in the mortar. Be certain the chosen mortar does not include language such as “interior use only” or “not for exterior use.”

While on the topic of bonding materials, be cautious of using organic adhesives in wet areas over membranes. The Handbook, in nearly all the Bathtub/Shower Walls and Shower Receptors details makes this comment: “Do not use organic adhesives to bond tile to a membrane or other impervious substrate.” The Setting Materials Selection Guide further states: “Adhesives are not suitable for swimming pools, exteriors or areas exposed to temperatures exceeding 140 degrees Fahrenheit.” Again, consult the manufacturer for specific use and suitability.  

When considering a tile installation in wet interior and exterior installations, be certain that the use and placement of expansion joints, as detailed in the Handbook method EJ171, is addressed.  All tile that is exposed to water will grow over time. While this growth is very small, the tile does not contract in size after the water is eliminated. If the expansion joints are not large enough to handle this growth, the tile may pop up or “tent” in the middle of the floor. Expansion joints are extremely important and necessary for a quality installation.

For exterior areas, any installation that includes a drain, and particularly stall showers, the floors must be sloped toward the drain to fully evacuate the water. The plumbing code typically requires membranes to be sloped a minimum of ¼ inch per foot and extend at least 3 inches above the height of the curb or threshold. Additionally, all surfaces in a shower must be sloped to the drain, including thresholds, curbs, seats, windowsills, niches and shelves.

Last, but certainly not least, is the subject of mold. Nobody wants or likes to see mold growth.  With a properly designed project, installation done by qualified labor and routine maintenance, the enjoyment of a wet-area installation will be achieved.