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Specifying ceramic, glass, and stone tiles for exterior and interior wet areas

All photos courtesy Ceramic Tile and Stone Consultants
All photos courtesy Ceramic Tile and Stone Consultants

by Donato Pompo, CTC, CSI, CDT, MBA
Exterior decks and balconies, and interior showers and bathrooms, have historically been problematic areas for the installation of ceramic, glass, and stone tiles. Typically, problems are due to installer error, not using appropriate materials, or not providing clear enough specifications. In each case, it is the result of not following industry standards.

These standards are created by industry consensus groups through organizations such as American National Standards Institute (ANSI), Tile Council of North America (TCNA), ASTM International, or International Code Council (ICC). These groups combine their many years of experience and science to establish standards so problems and failures can be avoided and not repeated. If the standards are not followed, then known potential problems cannot be circumvented.

In the last decade or so, since the demand and use of tile and natural stone has dramatically grown, there have been a lot more failures caused by those materials being subjected to excessive moisture. Obviously, tile and stone are resistant to problems as indicated by the many installations still functional after thousands of years of use and exposure to various weathering conditions. However, when things are done incorrectly in a tile and stone installation, particularly where water is involved, it can lead to aesthetic failures and substantial collateral damage of adjacent materials, significantly reducing the application’s life.

As a forensic investigator for more than 12 years, this author has investigated many failed exterior decks and balconies, and interior showers and bathrooms. The common denominators to tile and stone failures in these applications were the lack of proper slope, plugged weep holes, and inadequate flashing to contain or manage the water that resulted in various types of damages.

Need for moisture management
Frequently, exterior decks and balconies are subjected to water not only directly from rain, but also through drains and scuppers. These areas are also often washed down regularly, further subjecting them to large volumes of water.

As a useful comparison, one may consider the volume of water that showers are subjected to annually. If a person takes a 12-minute shower each day in an average-sized shower with reasonable water pressure and an appropriate shower head, the amount of water is equivalent to a roof being subjected to about 25,400 mm (1000 in.) of rain per year. Given these areas are likely to be subjected to more water than a typical roof, it is imperative extra care and attention is spent specifying and constructing them. This is accomplished by properly managing the water so it is controlled and safely evacuated from those areas.

The green algae on top of the limestone is the symptom of a moisture problem. Water was draining toward, rather than away from, the house as is required in the International Residential Code (IRC) for grading and foundations. Further, there was no vapor retarder under the concrete to keep the moisture away from the natural stone.
The green algae on top of the limestone is the symptom of a moisture problem. Water was draining toward, rather than away from, the house as is required in the International Residential Code (IRC) for grading and foundations. Further, there was no vapor retarder under the concrete to keep the moisture away from the natural stone.

Lack of adequate slope is a common problem in both exterior horizontal applications, as well as interior wet horizontal applications such as shower floors, shelves, and seats. It is clear in the tile and stone industry standards, as well as in the Uniform Plumbing Code (UPC)—International Association of Plumbing and Mechanical Officials/American National Standards Institute (IAPMO/ANSI) UPC 1—and the International Building Code (IBC) and International Residential Code (IRC), the slope-to-drain away from the building should be a minimum two percent slope. That calculates out at 6 per 305 mm (1/4 in. per 1 ft). UPC says the slope-to-drain in a shower must be a minimum of 6 per 305 mm (1/4 in. per 1 ft), but not more than 13 mm per 305 mm (1/2 in. per 1 ft).

It is important for this slope-to-drain to be at the surface of the tile or stone, but it is also critical the minimum 6 per 305 mm is at the surface of the waterproof membrane. Drains come in two sections. Where the drain clamps down on the waterproof membrane, below the surface of the tile assembly, there are weep holes in the drain so any water migrating to the membrane can then evacuate.

Sloping to drain
One of three common problems this author encounters is the waterproof membrane is not properly sloped to the drain. In a shower, this can result in the tile mortar bed staying constantly damp, leading the room to take on a musky odor; it may also cause a stone or tile floor to look wet, and the excessive moisture might result in the stone spalling (deteriorating) and/or staining.

Sometimes, the waterproof membrane is flat or even negatively sloped away from the drain, or there are low spots on the membrane surface where water collects. These same conditions can be found on an exterior deck or balcony. Obviously, an exterior deck or interior commercial floor with multiple drains is a somewhat complex installation for the waterproof and tile installers.

In these cases, one must transition areas peaking and sloping in one direction or the other toward the respective drain. It is critical to ensure the drains and slopes are properly laid out to allow for all the water reaching the membrane to readily evacuate through the drain weep holes. Even when there are drainage mats installed atop the waterproof membranes to facilitate the water’s evacuation from the mortar bed into the drain, there can be expensive problems if the membrane is not properly sloped.

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