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Members of the architecture and design community continue to demand high performance from the beautiful ceramic tile and stone installations specified in their projects. Today, professional, specialized contractors are asked to install these finishes in more places than the usual "wet areas" generally characterized by commercial kitchens and bathrooms. Tile and stone can be used in virtually any room of any building for functional purposes, or simply for its beauty.
However, due to the increased use of tile and stone in commercial interiors, builders have to adjust the way their structures are designed and built beneath ceramic tile and stone applications.
Traditionally, it’s been taken for granted that the structure could be of the same construct that’s beneath hardwood, resilient or carpeted areas, but with the increasing popularity of large-format tiles and stones – and longer spans for larger rooms – failures can occur if the structures aren’t designed properly. Builders must rely on strong interior design plans for these construction projects. The areas that receive ceramic tile and stone must be designed to a more rigid standard than those which are finished with other materials.
Structural Requirements for Installations
Before any work starts, the surface must be rigid enough to accept the tile or stone. The TCNA Handbook for Ceramic, Glass and Stone Tile Installations, published by the Tile Council of North America, explains that it’s the responsibility of the project architect, designer or engineer to determine if the substrate meets the proper stiffness and deflection criteria.
The substrate needs to meet the maximum allowable deflection for the finish and the installation system that will be installed. Deflection is the potential movement which the installation may experience when subjected to load and use. Ceramic tiles and stones are very rigid and thus will not be able to handle excessive movement in the substrate. All substrates therefore should meet the maximum allowable deflection rating of L/360 for ceramic tile and L/720 for stone applications installed over wood framed constructs. Some adhesive manufacturers will allow an L/480 deflection standard for stone applications.
It’s important to keep in mind that these maximum allowable deflection standards are very different from the L/360 design standard that’s called for in most building codes. The building code requirement applies to a uniformly applied load across the spans, but it’s not uncommon for ceramic tile and stone applications to be exposed to concentrated loads.
A good example is when a person is walking over a structure wearing high heels. This exerts a tremendous concentrated downward force upon a very small area. A person weighing 150 pounds and concentrating her weight load on a small heel is distinctly different than the same 150 pounds being uniformly distributed over the span of an entire floor. Appliances that sit on "legs" or wheels will also concentrate their weight load, as well. Therefore, when ceramic tile and stone floors are exposed to concentrated loads, the engineer and/or specifier must specify an appropriate substrate to accommodate it.
Some other things to note:
- What will the areas that receive the tile and stone be used for?
- How many people will be using that area?
The more people that will use a space, the more rigid the structure must be. A floor that is designed at a 40 pound total live and dead load may be suitable for usage by four or five people. But what if this business space changes and that same floor space is subsequently used regularly by 30 people? What may have been rigid enough for a small group of people may now be pushed beyond its deflection limits, which can cause cracking of grout, or even worse, cracking of tiles and stones.
Exterior glue plywood, cement backer units and concrete are the most common flooring types for builders. There are also many uncommon types which remodelers frequently come across. These include existing finishes like ceramic tile and stone or resilient flooring. They even run into substrates that still have old adhesives on them.
Tile and stone are able to be successfully installed over certain types of uncommon finishes, provided that proper precautions are taken.
With all tile and stone installations, proper surface preparation is perhaps the most important phase of the work. Even when it needs to be specifically addressed, not enough time or resources are generally allocated to ensure that this is done correctly. This scenario is especially true in renovation work. (One never knows what one may run into when starting to renovate a commercial interior.)
All substrates must be free of any bond-breaking or bond-inhibiting materials. These may include sealers, waxes, curing compounds, form release agents, paint, dirt, grease, oils, old carpet adhesives or other contaminants. They must be completely removed prior to the tile or stone installation.
One of the best ways to remove these contaminants is via the mechanical abrasion method. Usually, the contaminants have penetrated into the substrate's pores and will block an adhesive's ability to create a mechanical bond or attachment to the surface. It’s not good to use chemicals or acid to strip/remove these contaminants. Chemicals or acids may penetrate into the substrate and will become virtually impossible to remove.
Commercial renovations present a potential number of problems to consider:
If you find existing hairline cracks on a concrete substrate, use an anti-fracture membrane to help reduce the transmission of the cracks to the tile or stone.
Protection from water damage is another area to be addressed both from the positive and negative side. Although times are changing, most tile and stone used is still in wet areas of the interior. It’s important to remember that tile, stone and grout aren’t completely waterproof. Today's buildings need to be protected from potential water damage from spaces above or from adjacent areas.
Most adhesive manufacturers provide thin, load-bearing positive side waterproofing membranes which are compatible with their adhesive and grout mortars. Waterproofing membranes also protect the structure itself and the construction cavities against water damage, minimizing the potential for stain-causing mold and mildew. In addition, moisture mitigation membranes/treatments may be required when installing moisture sensitive finishes or when moisture sensitive installation materials are used within the assembly.
Expansion allowance should also be included in all tile and stone installation systems. Above grade, exterior, wet area and installations exposed to direct sunlight will require more frequent and wider expansion joint placement.
The designer should provide direction on the design, placement and construct of all expansion joints. If the designer can’t provide specific jobsite information/requirements, the TCNA Handbook for Ceramic, Glass and Stone Tile Installation provides information on the design, placement and construct of expansion joints – reference TCNA information section EJ171 for additional information.
For example, for interior dry areas, the expansion joints should be placed a maximum of 25 feet in each direction in the field of the installation, at all perimeters, against restraining surfaces and at changes of plane. The sealant chosen for these joints should be durable, weather-resistant and able to handle any movement the installation will be subject to. Typically, silicones and urethane sealants are best for these applications. Most sealants produced will match the grout colors used. Latex or acrylic caulks should not be used for these applications. They are only suitable for interior, non-wet, non-traffic areas.
Porcelain vs. Ceramic Tile
Porcelain tiles are the most popular type of tile (including thin gauged porcelain tile, panels and slabs) in use today. They have a very low porosity rate – generally less than 0.5%. A typical ceramic-bodied tile usually has a porosity rate of 3% or even greater. This means that your adhesive mortar needs to have a greater ability to formulate a bond with the back of the much denser porcelain tile, or the mortar will not have the ability to penetrate or absorb into the body of the tile and mechanically "grip" it (like it can with a more porous ceramic-bodied tile). A conventional dry-set or low-end thin-set mortar will not provide the desired results for porcelain tiles.
For best results, specify a suitable, latex-fortified thin-set mortar to install porcelain-bodied tiles. These are ANSI A118.4, ANSI A118.11 or ANSI A118.15-compliant thin-set mortars. The Tile Council of North America clearly requires that a latex-fortified thin-set mortar be used to install porcelain-bodied tiles. It’s recommended that you check with your adhesive manufacturer for a single source comprehensive installation system that is fully warranted for labor and materials. This process will ultimately provide builders, renovators and end-users peace of mind for years to come.
What type of grout should be used in today's commercial interiors? Building owners and facility managers are demanding low-maintenance materials in every area of their structures. Floors, walls and countertop installations fall into this arena.
Historically, grout has been the hardest part of a tile or stone installation to maintain and keep clean. There are grouting materials which address this concern. Epoxy-based grouts are available and have a porosity rate of less than 0.5%, and therefore never need to be sealed. Just think of the labor and materials cost savings realized by not having to seal the grout every year.
Today, special single component (ready-to-use) technology grout is also available with special features: it offers antimicrobial protection to inhibit the growth of stain-causing mold and mildew, has low volatile organic compounds, is available in a wide array of color offerings and can even be specified with sparkling or glow-in-the dark features. This special grout provides all the benefits of epoxy grout and is as easy to install as cement-based grouts, making it a popular choice among customers. These grouting materials are also included in the adhesive manufacturer's comprehensive warranties. This adds great value to the final, completed building project.
Arthur Mintie is senior director of technical services with LATICRETE International Inc., a global manufacturer and marketer of installation systems for ceramic tile and stone and construction chemicals used in commercial, industrial and residential applications. Visit www.laticrete.com for more information.
This article was originally published in June 2011 and updated March 2020.