Another premise that we need to understand is that a tile installation is not waterproof in and of itself. That may sound unusual, but there are people who believe that tile on any surface creates a waterproof environment. This is not true, and the failure of the substrate material causes the tile to also be considered a failure when in actuality the tile may have had little or nothing to do with it.
Specifying the appropriate tile
No one wants a tile failure due to moisture; consequently it is incumbent upon each person involved in a tile installation to do his or her part. This would include architects, specifiers, manufacturers, distributors, retailers, designers, and lastly, tile installers. Many times, the installer, normally one of the last people on the job, is viewed as the culprit in a failure. However, if proper methods and/or manufacturer’s guidelines are followed to the letter, the installation should -- and will -- function well. If not, most times they will fail. The real question is, “Who in this chain of command specified the products or the system used?”
There are many methods in the TCNA Handbook that speak to the issue of installing tile in areas affected by moisture. In fact, the 2012 edition makes this statement under the heading Materials in the details; “Multiple options exist for membranes, mortars, grout and other materials and MUST BE CLEARLY SPECIFIED to be included. If not specifically indicated, optional materials are not included and mortar/grout choice defaults to minimum performance specification indicated. Consider each system component and intended use to determine minimum requirements and to specify options.”
The person who specifies what is to be used and what is to be done could be anyone from the list of players in the last paragraph. This individual shoulders the responsibility of providing the appropriate method selected and the materials used.
Areas that encounter small amounts of water in a home would be the kitchen countertop and backsplash and the whirlpool tub. Normally, these areas see limited amounts of water, but can have significant quantities of water given the fact that some folks are more careless with the amount of water used, and whether or not it is removed in a short period of time. The safest practice here is to include a waterproof membrane to be certain that the substrate and/or framing beneath are not compromised.
The major water-containing site both residentially and commercially is the stall shower. In a perfect world, large amounts of water move from the shower head to the drain. The difficulty here is to treat the areas in between in a fashion that will continue the water in that path. The use of a waterproof membrane, whether it is liquid or sheet, segregates the wet from the dry area. These topically applied membranes, placed between the tile and the substrate, function to keep the water away from the wall cavity.
Further water management is mandated in the Handbook calling for all surfaces to be sloped or pitched to the drain, including the shower floor and seats. The plumbing code typically requires membranes to be sloped a minimum of ¼ inch per foot. Likewise, entrance thresholds, niches, shelves and window sills should slope to the drain to ensure that no standing water remains in these areas.
95% mortar coverage
Another aspect of the tile installation in wet areas which is required by both the ANSI Specifications and the TCNA Handbook is the 95% mortar coverage on the back of the tile. These guidelines call for the mortar coverage to be evenly distributed to support edges and corners. When this almost-to-full coverage is achieved, there is no room for latent water to accumulate behind the tile, causing certain portions of the grout to appear wet and dark rather than dry and uniform in color.
Exterior tile installations function similarly to shower floors. They must be sloped or pitched to evacuate the surface water to a floor drain, scupper or edge; they require a minimum of 95% mortar coverage and properly designed and installed movement accommodation joints. These three requirements are essential for a successful exterior installation and mandatory in areas affected by freeze-thaw conditions. If water is allowed to gather in these areas, the expansive nature of freezing water will eventually cause the tile to come loose and crack. Once this occurs, additional water can enter the tile installation and further exacerbate the problem.
Additionally, the tile type must be considered in order that it will function properly. Some natural stone products and highly absorptive unglazed tiles may soak up large amounts of moisture and cause an unsightly appearance. Many times, the application of an impregnator may solve this problem, but it is best to consult the manufacturer to determine the best product for the job. Generally, tiles that are considered to be semi-vitreous (3 to 7% absorptive) and non-vitreous (7 to 20% absorptive) should not be used in exterior wet areas where the temperature will fall below freezing.
Using compatible products
Each of the aspects of tile installations talked about here is important, but there is one final piece to this puzzle that is imperative for success. Use products that are compatible with each other. While this sounds like a no-brainer, it is often not considered. One last recommendation is to use installation products made by one manufacturer, when possible. Consult their technical service department and ask them for a complete specification covering all facets of the project -- along with their warranty to back it up.
As stated at the outset, water always wins. However as we have seen, if properly specified, installed and maintained, water can be managed and kept exactly where we want it to go -- down the drain. Moving moisture from the source, across the tile surface and away from the tile assembly provides for a successful tile installation that will function for many years without issues.