Trying to install tile in wet areas is a big deal. That's because wet areas present substantial challenges that must be addressed prior to the tile installation. And, if you don't carefully consider the location of your installation, then the beauty, functionality, durability, and longevity of ceramic tile are of little value.
Let's explore then what's involved and what you need to install tile in wet areas.
Defining Wet Areas for Tile Installation
What is a wet area tile installation?
The Tile Council of North America (TCNA) Handbook provides an explanation in the Environmental Exposure Classifications section. There are also 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 include 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 walls, shower walls, and enclosed pool area walls.”
There is a misconception that tile is waterproof which must be corrected through tile-related education. The tile surface, either glazed or unglazed, may repel water, but other than a porcelain tile, the body of the tile is absorptive at various degrees.
The only way to stop the movement of the water into the structure of the building is to provide a positive water barrier behind the tile and, if required, a load-bearing capacity.
Four Requirements for Installing Tile in Wet Areas
All surfaces in a wet area must slope toward the drain including a niche as seen in this image.
Step 1: Slope Surfaces Toward the Drain
Exterior areas that include a drain and stall showers must be sloped toward the drain to fully evacuate the water. The plumbing code requires the floor to be sloped a minimum of ¼” per foot to a maximum of ½” per foot.
Additionally, all surfaces in a shower, including thresholds, curbs, seats, windowsills, niches, and shelves, must be sloped to the drain.
Last, but certainly not least, is the subject of mold.
Nobody wants or likes to see mold growth, but it can be controlled. Mold requires three things to flourish, a food source, a supportive environment, and water. If water is properly directed to the drain, mold can be minimized. With a professionally designed project, installation done by qualified labor, and routine maintenance, the enjoyment of a wet area installation will be achieved.
>> See Does Your Tile Slope To the Drain?
Step 2: Select a Waterproof Membrane and Mortar
Choosing the appropriate waterproof membrane is an excellent way to segregate the water from the substrate. These products come in three basic categories: liquid-applied, fabric-reinforced, and sheet. Each is designed to accomplish three objectives.
- Bond tenaciously to the surface which is being protected.
- Support the weight of the tile being installed.
- Prevent water from entering the substrate efficiently and effectively.
Liquid-Applied and Fabric-Reinforced Products
The liquid-applied and fabric-reinforced membranes range from a creamy to a gel-like consistency and are applied over several manufacturer-approved substrates. 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 between coats. The use of a wet film thickness gauge is an excellent way of obtaining the required thickness.
Sheet Waterproofing Membranes
Sheet waterproofing membranes are available in several widths, thicknesses, and compositions. Depending on the manufacturer, they range in width from 39-3/8” (1 M) up to 72” (1.83 M) and vary from four to forty mils in thickness. The product composition may be chlorinated polyethylene (CPE), polyethylene, or polyvinyl chloride (PVC) which are 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 completely and without deviation.
Combining products and/or methods from various manufacturers is a recipe for failure which will not be covered by the manufacturer’s warranty.
Uncoupling Membranes
An additional product is 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 from the substrate, can also provide a waterproofing capacity if the product joints and wall connections are installed according to the manufacturer’s recommendations.
>> See The Ultimate Guide to Underlayment for Tile
Consult the TCNA Handbook for Proper Membrane Options
Many of the methods and details contained in the 2024 TCNA Handbook provide a section entitled, “Membrane Options.” For example, under Shower Receptors, method B415 states the following:
- A waterproof membrane (A118.10) or vapor retarder membrane (A108.M-2.8.1) must be specified for walls 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 the 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 the 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 to deliver the desired result.
This may sound like a broken record but always consult the manufacturer for specific instructions since one size does not fit all and can result in failure.
Step 3: Chose a Mortar That is Recommended for Use in Wet Areas
Always Consult the Mortar Manufacturer for Instructions
Many of these products call for a Dry-Set or more popularly known as thin-set mortar to be used to either bond the sheet membranes to the substrate and/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) Modified Dry-Set Mortar (A118.11), or the latest addition to this category, an Improved Modified Dry-Set Cement Mortar (A118.15).
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. In the Handbook, many of the Bathtub/Shower Walls and Shower Receptors details make these comments:
The Limitations section states,
“When organic adhesive is used – not for areas exposed to temperatures exceeding 140° F.” (Some details call for temperatures not exceeding 125° F.)
“Organic adhesive may be used on walls only; do not use on floor or curb.”
The Notes section states,
“Do not use organic adhesives to bond tile to a membrane or other impervious substrate.”
Again, always consult the manufacturer for specific use and suitability.
>> See Do You Ignore Grout Manufacturer Directions?
Step 4: Always Install Movement Joints
When considering a tile installation in wet interior and exterior installations, be certain that the use and placement of movement joints, as detailed in the Handbook method EJ171, are addressed. But remember, according to EJ171, “The design professional or engineer shall show the specific locations and details of movement joints on project drawings.” Tile mechanics install these joints but they do not design or locate them.
All tile that is exposed to water will grow over time. While this growth is small, the tile does not contract in size after the water is eliminated. If the movement joints are not large enough to accommodate this growth, the tile may pop up or tent in the middle of the floor.
These joints are extremely important and necessary for a quality installation.
>> Why Do You Need Expansion Joints When Installing Tile?
>> Quick and Easy Movement Joints... the Right Way
Are You Ready For Installing Tile in Wet Areas?
I hope you feel better prepared to successfully install tile in wet areas. This knowledge and standards-based approach to tile installation is an important part of the CTEF mission, curriculum, and certification programs. Consider learning more about the Certified Tile Installer program.
Thanks for reading and please tell your friends where you found this information.
Scott
