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

by Catherine Howlett | May 1, 2013 3:52 pm

All photos courtesy Ceramic Tile and Stone Consultants[1]
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.[2]
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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This is a shower pan substrate under the waterproof membrane that is wet due to a leak in the membrane. The plumber’s level shows the surface is not sloped to drain as it should be. The red arrow is pointing to black microbial growth on the wood shower dam, indicating water was getting to the wood dam.[3]
This is a shower pan substrate under the waterproof membrane that is wet due to a leak in the membrane. The plumber’s level shows the surface is not sloped to drain as it should be. The red arrow is pointing to black microbial growth on the wood shower dam, indicating water was getting to the wood dam.

Plugged weeps
The second common drainage problem this author sees involves plugged weep holes. Industry standards state the weeps are to be covered with pea gravel or with a plastic protector to ensure the holes stay open. Often, this weep protection is left out, and the mortar is placed over top the holes, plugging them. Thus, if the waterproof membrane is properly sloped to drain, the water cannot escape into the drain. Again, this leads to musky odors, wet appearance, or stone spalling and staining, as previously noted.

In some instances, both the weep holes are plugged and the membrane is not properly sloped to drain. A good example of multiple compounding deficiencies is an exterior deck this author investigated that had a natural stone on its surface. The stone had badly spalled in some areas after a few years of use. An intrusive inspection of the tile assembly revealed it had a primary waterproof membrane under a drainage mat that was below a mortar bed to which the stone was attached.

Not only were the weep holes plugged, but when water was poured over the membrane where a stone had been removed, it flowed away from the drain, despite being only 305 mm (12 in.) away. A hose was run for 15 minutes and the water never reached the drain—the waterproof membrane was clearly not properly sloped. Essentially, there was a reservoir of water stored under the stone installation, replenished by rain and weekly deck maintenance. This constant and excessive exposure to moisture migration resulted in the stone becoming badly spalled and stained.

Spalling is typically caused by moisture migrating from the stone’s underlying substrate up through to its surface where the moisture evaporates. As the moisture travels from under the stone through the cementitious materials, and through the stone itself, the moisture picks up various minerals (i.e. salts) that dissolve in the moisture. When the moisture reaches the stone’s surface, it evaporates—the minerals precipitate into solids again. This expansion or crystallization of the mineral, referred to as efflorescence, causes the surface of stones to deteriorate to some degree. With constant cycles of evaporation of moisture at the surface, this can badly deteriorate and/or stain the stone.

In this photo, the seam in the shower pan waterproof membrane was not installed correctly and allowed water to migrate through.[4]
In this photo, the seam in the shower pan waterproof membrane was not installed correctly and allowed water to migrate through.

Incomplete waterproofing or vapor retarders
In some projects, waterproofing or vapor retarders are not complete or continuous; they tend to lack flashing at transition areas. Considering the potential collateral damages a defective balcony can incur, it is important to construct it like a big shower pan. Assuming the deck has been properly pre-sloped, the waterproof membrane must continue, or be flashed, up the wall at least 76 mm (3 in.) above any thresholds to prevent water from causing any potential collateral damages.

All seams and transitions must be properly sealed or flashed. These are the areas most vulnerable to problems, so they need extra attention to ensure they are correctly installed. All penetrations must be properly waterproofed, flashed, and sealed with a sealant. The waterproof membrane should never be penetrated, unless it is unavoidable, and then the penetration has to be properly flashed and sealed with the appropriate sealants to ensure it never leaks.

When the decks have drains, they should be strategically placed to not only allow for adequate drainage, but also to make sure the selected tile can manage the various slope transitions. For example, larger tiles are limited in accommodating slopes and transitions than smaller units.

This author often finds decks are sloped to the outer edge without any type of gutter or drain. The water drains over the side of the balcony and eventually results in staining along the stucco, or staining and spalling the stone siding.

The latest trend is to use trench or lineal drains that can be installed at the perimeters of decks or showers. The trench drains can be installed so the tile or stone is attached to the center, enabling it to blend within the flooring and allowing drainage around the tile edges. There are gutters designed for tile that can be installed at the perimeter edges of decks so the water runoff can be controlled and directed into drains. It is never a good idea to let water runoff the edge of decks. Water should always be directed into drains or scuppers connected to irrigation drainage.

Another big issue in terms of the lack of continuous moisture or vapor barriers and flashing is with on-grade slabs. ASTM E1643, Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs, states the vapor retarder is to continue from under the slab and up the sides of the slab and footings. This is the only way to keep moisture from the landscape soil to migrate laterally into the slab on the exterior decks as well as migrating into the interior areas of the slab.

Some pool decks do not have a vapor retarder; others do, but typically do not continue up the sides of the slab. In either case, the landscaping may be butted up to the slab edge, and even the stone edge. This allows the water full of minerals from the soil to migrate ultimately into the stone surface, resulting in spalling, staining, and other potential problems.

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In terms of regular showers and steam rooms/showers, continuous waterproof membranes and flashing are critical. Shower tubs and shower pan receptors should be waterproofed and flashed with the wall vapor retarders to provide a continuous path for water to reach the drains.

This badly spalled limestone tile is from a high-rise exterior suspended deck. Although it had a drainage mat over a waterproof membrane, the latter was not properly sloped to the drains and weep holes were plugged. This resulted in the stone being subjected to continuous moisture that caused the spalling.[5]
This badly spalled limestone tile is from a high-rise exterior suspended deck. Although it had a drainage mat over a waterproof membrane, the latter was not properly sloped to the drains and weep holes were plugged. This resulted in the stone being subjected to continuous moisture that caused the spalling.

Tubs and prefabricated shower receptors should have a minimum 25-mm (1-in.) flange at their edge so the wall vapor barrier overlaps it to ensure the water travels toward the drain and avoids getting behind those receptors. Often, those receptors do not have the 25-mm flange. Either way, this author always recommends taking a bitumen flashing material, with the self-adhesive front and back, and have those transitions flashed 152 to 305 mm (6 to 12 in.) from the receptor edge to the wall, and overlapped with the wall vapor retarder.

This author also recommends flashing the inside corners of the shower framing and at the transition of shower pre-sloped dams, seats, and shelves. Anywhere there is a transition in a shower application, there is a potential for a breach allowing moisture to migrate into the wall cavity, which can result in huge collateral damages.

Per UPC and industry standards, the waterproof membrane is to extend over the face of the dam and outside the rough jambs of the shower opening at least 76 mm (3 in.). Waterproof folds, laps, and reinforcing webbing must extend at least 102 mm (4 in.) in all directions from the corner. This is even more critical in steam rooms, particularly if they will be used frequently.

Steam rooms or steam showers require even more care and protection. There should be insulation boards installed behind the low-perm vapor retarder. All transitions should be properly flashed. Movement joints should be installed at all transitions using sealants meeting the industry-required ASTM C920, Standard Specification for Elastomeric Joint Sealants, and suitable for the intended use, whether it is a regular shower or a steam room. This includes inside corner transitions at wall-to-wall, floor-to-wall, and seat-to-wall corners, at the respective outside corners, and around all penetrations.

The movement joints provide protection not only against expected movements within the structure and materials (i.e. dynamic structural, moisture, and thermal movements), but also to keep water out of those vulnerable transition areas. Steam rooms need special steam-proof doors and light fixtures, and they need to be sealed at their perimeters as well as at plumbing wall escutcheons and flanges. The acrylic, latex, or siliconized sealants do not meet ASTM C920 requirements and they do not perform well over time.

Specifying and MasterFormat
How can architects help ensure exterior decks, balconies, and showers are given the attention they need to avoid failures? It is the same old answer: write a project-specific detailed MasterFormat specification that is complete, concise, correct, and clear. In the specification it is not only important to specify the appropriate reference standards in Part 1–General and the correct products in Part 2–Products, but it is also critical to specify the key steps of the installation in Part 3–Execution.

It does not matter who is at fault when there is a problem—everyone ends up paying, either in time to defend themselves, money to fix the issue, or with their reputation. It is in everyone’s best interest to ensure installation specifications are thorough, clear, and unambiguous. The following paragraphs summarize the key content that should be in specifications for tile and stone installations for exterior decks and balconies, and interior showers.

Part 1–General Requirements

  1. The key industry standards must be called out:
  1. A specific quality assurance (QA) section needs to be prepared to verify material performance and suitability for the intended application.
  2. Single-source responsibility from an installation product manufacturer should be required, and should include a minimum 10-year labor and material manufacturer warranty. The product quality required for the extended warranty is much higher, and it ensures compatibility between all products. It is also important to require a letter in writing be provided from the manufacturer, before installation, stating its products are suitable for the application.
  3. Tile-installers—both setters and helpers—should be certified or verified in order to demonstrate they know and are current with industry thin-set standards (e.g. Certified Ceramic Tile Installers [CTI] through the Ceramic Tile Education Foundation [CTEF] or Tile-installer Thin-set Standards [ITS] verification through the University of Ceramic Tile and Stone [UofCTS]).
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Part 2–Products

  1. The specifications should be performance-based. Reference specifications only call out products meeting the minimum requirements, which are essentially the least-expensive products with the lowest acceptable level of performance.
  2. Stone should meet ASTM minimum/maximum physical property requirements for their respective geological classification. Ceramic tile should meet ANSI A137.1 standards, and glass tile should meet ANSI A137.2 standards.
  3. Installation products should be provided by a single-source manufacturer who provides a minimum 10-year labor and material warranty. Thin-set adhesives should meet or exceed ANSI A118.15, American National Standard Specifications for Improved Modified Dry-set Cement Mortar, for higher performance.
  4. Waterproof membranes must meet ANSI A118.10, American National Standard Specifications for Load-bearing, Bonded, Waterproof Membranes for Thin-set Ceramic Tile and Dimension Stone Installation, and ANSI A108.02 requirements. Perm rate for steam rooms/showers needs to be specified. Waterproof membranes on exterior decks or balconies over occupied spaces must be a primary roofing membrane.
  5. Sealants for movement joints must meet the appropriate ASTM C920 requirements for the application. They must also be installed with polyethylene backing and primers per sealant manufacturer requirements.

 

When decks are installed correctly, they can look beautiful and perform flawlessly for many years, as is the case for these limestone columns and covered and exposed deck flooring. The horizontal surfaces have adequate slope to allow the water to flow into the property drainage system. Stone was isolated from landscaping and had a vapor retarder underneath. [6]
When decks are installed correctly, they can look beautiful and perform flawlessly for many years, as is the case for these limestone columns and covered and exposed deck flooring. The horizontal surfaces have adequate slope to allow the water to flow into the property drainage system. Stone was isolated from landscaping and had a vapor retarder underneath.

Part 3–Execution

  1. The specific installation method and detail from TCNA Handbook for ceramic, glass, and stone tiles must be specified.
  2. It must be noted in Division 03–Concrete that concrete substrates are to meet ANSI A108.01 tolerances and surface textures in preparation for tile work.
  3. Substrates for exterior decks and balconies, and interior showers, must be sloped to drain at 6 per 305 mm (1/4 per 12 in.). The type and location of drains need to be specified.
  4. Installers must be required to inspect substrate conditions before commencing with the installation. When there are any obvious defects or conditions preventing a satisfactory tile installation, the installer is to notify (per ANSI A108.02) the architect, general contractor, or other designated authority in writing, and is not to proceed until satisfactory conditions are provided.
  5. When concrete surfaces do not readily absorb water or have any type of contaminate, they must be scarified until the surface is acceptable. When the concrete surfaces in wet areas do not meet the required 6 per 305-mm slope-to-drain or the ANSI A108.02 tolerances, they must be corrected by the concrete subcontractor.
  6. A movement joint layout plan needs to be provided, and the architect must specify types of movement joints as referenced in TCNA EJ171 Movement Joint Guidelines. The tile installer should be instructed to submit Requests for Information (RFIs) if he or she is not clear with the requirements.
  7. It should be specified that substrates are to be cleaned with no contaminates and must readily absorb water. It should also be specified that the backs of the tiles and stones must be cleaned.
  8. The specifier should state waterproof membranes are installed per manufacturers’ directions and must be continued up walls over any horizontal surfaces, and over any dam. Flashing should be detailed in the plans shown at all appropriate transitions. Waterproofed areas should be flood-tested per ASTM D5957, Standard Guide for Flood Testing Horizontal Waterproofing Installations.
  9. In the specifications, it should state drain weep holes must remain open and protected with an appropriate amount of pea gravel or with a weep hole protector cover.
  10. It should be specified that tile and installation products must be installed per manufacturers’ instructions and industry standards. Products should also be mixed per manufacturers’ instructions. Temperature limitations must not be exceeded, and shading or heat must be provided as required. Also, work is to be protected from both weather and other trades.
  11. For exterior and wet interior areas, it must be specified the adhesive contact between the tile and its substrate is to be 95 percent with no voids at corners or edges (and with no voids larger than 50 x 50 mm [2 x 2 in.]). Voids in wet areas will collect water and can result in efflorescence and spalling problems.
  12. A detailed quality control plan, to be implemented by a third party, must also be provided.

Conclusion
Exterior decks and balconies, and interior wet areas, are more prone to problems because of their exposure to large volumes of water. Failures of these areas are typically due to a combination of installer error, improper material use, and not having thorough specifications and details. Three common deficiencies found are the lack of an adequate slope-to-drain at the waterproof membrane surface, plugged drain weep holes, and the lack of adequate waterproof flashing to keep moisture from migrating into the substrate and tile or into adjacent materials causing expensive collateral damages.

To avoid these problems, architects must write detailed specifications that are specific, complete, and clear. Installers must be current with industry standards, and follow those standards and the manufacturers’ directions while installing the tile. Installers are mechanics with the skill to provide quality workmanship, but they should not be expected to make architectural decisions—architects must give the installers the details they need to do their job correctly.

Most installers learn their skill on the job and do not have the opportunity to learn the industry standards. So it should be specified and verified the tile-installers are up to date with the current industry standards.

This author has never investigated a tile or stone failure and found all the industry standards and manufacturers’ instructions were followed. It is always the opposite. The failure is never due to one deficiency, but is always because of many compounding problems. Simply put, the key to a successful tile and stone installation is to follow industry standards and write good specifications.

MasterFormat and SectionFormat provide the structure for good-quality specifications, which if used correctly and thoroughly, will limit risk and liability when specifying ceramic tile, glass tile, and stone applications.

Donato Pompo, CTC, CSI, CDT, MBA, is the founder of Ceramic Tile and Stone Consultants (CTaSC), and of the University of Ceramic Tile and Stone (UofCTS). He has more than 35 years of experience in the ceramic tile and stone industry from installation to distribution to manufacturing of installation products. Pompo provides services in forensic investigations, quality control (QC) services for products and installation methods, training programs, testing, and onsite quality control inspection services. He received CSI’s 2012 Construction Specifier Magazine Article of the Year Award. Pompo can be reached at donato@ctasc.com[7].

Click here[8] to read the article Case Study: Shower failure.

Endnotes:
  1. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/05/SandstonePoolDeckSpallingEfflorescence.jpg
  2. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/05/LimestonePoolDeckFailureAlgaeSymptomNoSlopNoVaporR.jpg
  3. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/05/PreSlopeLevelNotSloped.jpg
  4. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/05/membraneSeamImproper.jpg
  5. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/05/PoolDeckLimestoneSpallingEfflorescence01.jpg
  6. [Image]: http://www.constructionspecifier.com/wp-content/uploads/2013/05/SuccessfullLimestoneExteriorDeckResidence1-copy.jpg
  7. donato@ctasc.com: mailto:donato@ctasc.com
  8. here: http://www.constructionspecifier.com/case-study-shower-failure/

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