Setting material manufacturers have been diligent in developing many new products to aid big tile installation. Many of these new products are highly engineered and task specific. In the past, most manufacturers worked on a Good, Better, Best system. These traditional thinset products provided different levels of performance for typical sized tile of the day and are still adequate for many of today’s larger tile product applications; but often with current construction techniques, consumer expectations, and installation requirements, sometimes tile installations benefit from task-specific products.
Environmental conditions affecting setting material considerations may include but are not limited to: the type and condition of the substrate, the desired drying time prior to traffic, the flatness of the substrate, temperature and humidity conditions of the job-site and the in- service use of the ceramic tile floor. Under these conditions installations can often benefit from use of specialized setting materials. We see many installations currently being done using traditional and time-honored products by seasoned tile installers who insist on using products they are familiar with when they are not appropriate for the installation conditions. Probably the biggest error in this area is using a standard thinset where a medium bed is appropriate.
Without question, setting materials manufactures have responded well to the bigger-is-better trend with appropriate bonding materials. Unfortunately that same foresight has been lacking in those who provide the structures and substrates we install over. Neither architects nor builders are providing the flatter floors that popular formats and patterns require. In my opinion that is due in no small part to our failure as an industry to educate them in the requirements. Often in the course of the sale or specifying process nobody wants to acknowledge the tighter tolerances for substrates required by such large brittle clay and mineral-based surfacing material. The popular choice of staggered rectangular tile complicates things a little further due to natural and inherent warpage accentuated by placing the end of one tile at the middle of another, making it even more intolerant of undulating surfaces.
Very large tile requires what is known as super flat floors. While it is possible to specify the necessary tolerances during the building process, they come at a substantial additional cost. The skilled labor able to produce such surfaces can also be challenging to find. The tile industry flatness recommendation of ¼” in 10’ is adopted and reflected in the tile industry documents but is a recommendation published by the wood and cement trade organizations. These recommendations came about long before it was even possible to manufacture the tile sizes that are common today. Recently there has been some movement to acknowledge the need for flatter floors. The American Concrete Institute (ACI) publishes recommendations for slab work that is incorporated into both the Tile Council of North America Installation Handbook and the American National Standards for the Installation of Ceramic Tile. ACI has recently published a new document that addresses many concrete issues relative to flooring products including flatness. This document, ACI 302.2R-06 provides suggestions for dealing with various issues that typically arise. If you deal with concrete slabs extensively using any type of floor covering you would find it a very useful document in providing fact based information for educating everyone affected. It is available at www.concrete.org. Of course much of our work takes place over existing slab work installed sometime ago. When that is the case, attempting to correct out-of-plane conditions with thinset while installing tile is very labor intensive and often results in an unsatisfactory installation. Floor filling underlayment products, self levelers, or even mortar beds may be required to achieve satisfactory flatness tolerances needed for large tile in many instances.
The next big challenge in large tile is selecting the appropriate bonding material. This is where we can easily prevent problems. Selecting the appropriate thinset does not have to be a daunting task but you must consider both the site conditions and end use. If you are fortunate enough to have a flat surface you may want to consider a contact mortar. Contact mortars are designed to trowel smoothly and flow when under the tile to achieve coverage. With very large tile or if the area needs to be quickly returned to in service conditions, a rapid set version may be available. Contact mortars may allow for troweling and eliminate the need for back buttering large tile in some cases. If, however, the tile needs to be back buttered due to irregularities in the tile or substrate, a medium bed mortar would be more suitable. Using a traditional thinset where additional build-up is required is a recipe for disaster we see all too often. Regular thinset is designed for a side profile thickness of 3/32 to 3/8 of an inch. When used in thicker applications it loses its ability to bond and shrinks excessively causing fractures in soft tile and stone and possibly bond loss on dense tile such as porcelain. When installing any tile on walls, but large tile in particular, some of the new lightweight or non-sag thinsets offer superior bonds and faster drying times than conventional thinsets or mastics. Most mastic also has a maximum tile size limitation, typically 8”x8”. This is due to their inability to dry when used under large tile or thicker applications.
When selecting the appropriate trowel, not having thinset squish out of the joint is not part of the selection criteria! Industry recommendations for coverage are 80% interior areas and 95% wet or exterior installations. Selection depends on various reasons such as floor texture, tile backs, and floor flatness among a few. With very large tile, naturally occurring warpage may also influence the notch required to achieve coverage. For many years the primary acceptable thinbed method of installing large unit tile has been to trowel the floor and back-butter each piece of tile. This remains an industry recommendation and a sound method of installing large tile. In the mid ‘90s, research by the National Tile Contractors Association showed that using a U-notch trowel and combing all the ridges the same direction followed by placing the tile perpendicular to the ridges with a back and forth motion achieved the needed coverage without back buttering in some instances. Applying thinset to the back of the tile is always a good thing but very time consuming in today’s competitive environment. It does not eliminate the need to trowel the floor as well. Setting material manufacturers continually research products to achieve good coverage with minimal effort. Tool manufactures have also stepped up their research in this area. Several have come up with some oddly appearing notch configurations with amazing differences in coverage when compared to a conventional trowel configuration. Personally, I have found these to be the simplest way yet to achieve good coverage under the tile. What ever your choice of methods, there is no right or wrong as long as you get good coverage under the tile.
A big tile article would not be complete without a discussion of grout joints and “rectified tile.” Rectified tile is squaring the tile on all sides by cutting or grinding so that measurable variance from tile to tile is minimized. The January 2008 FCI issue contained an article on rectified tile and grout joints. At five pages in length it is much more through than a paragraph here will allow. The article can be reviewed at the FCI website (www.fcimag.com) article archive for that issue. If you missed that issue there are important new developments in the area of standards that will aid the installer substantially such as minimum grout joint width and new limitations on tile size, warpage, and thickness variations. My last words of wisdom: big tile and small grout joints still need movement joints. Even the perfect job is not going to stay that way if the installation cannot move as needed when required.