As the tile industry continues to grow, so does the size of the tile. Better technology is not only making large format tile readily available, but the quality is continually improving and selection is expanding. And consumers love it. Bigger tile means less grout and easier maintenance. I remember when large unit tile, 12” by 12” at the time, first appeared with regularity 20 to 25 years ago. Prior to that, 6” by 6” quarry tile was everywhere with a little glazed 8” by 8” mixed in. Salespeople were eager to pitch consumers on this slightly larger format calling it the “cutting edge of fashion.” They gleefully noted how much easier it is to care for because less grout is used. There was also a promised benefit for the installer; bigger tile meant faster installation and more money.
Manufacturers of setting material have developed many new products to accommodate bigger tile. Many are highly engineered and task specific. In the past most manufacturers relied on a Good, Better, Best system. These traditional thinset products provided different levels of performance and are still adequate for many of today’s installations. Even so, with the construction techniques now in use, increased consumer expectations and the installation specs required for very large tile, the setting material requires special consideration. You need to go with something that is based on the specific needs of the job. One-size-fits-all will not do it. You need to look at the type and condition of the substrate, the desired drying time prior to traffic, the flatness of the substrate, environmental conditions of the job-site and the in-service use of the ceramic tile floor. These conditions often require use of highly engineered latex or polymer modified product. Too often that requirement is overlooked. We still see many seasoned installers sticking with the time-honored products they know and love.
An 18” or 24” tile has additional performance needs in most applications that are difficult to achieve with traditional thinsets. All too frequently, when we see some of the newer, better performing products employed, they are often used in the same fashion as the traditional products: inadequate mixing time and too much water. Installers have been doing this for years. It cuts down waiting time and makes the thinset more “trowelable”. But this use of traditional mixing techniques completely negates the value of a task-specific performance mortar. You can end up with unacceptable characteristics up to and including complete failure. If the enhanced performance is to be realized, the instructions must be followed. It is that simple.
Large tile requires what is known as “super flat floors” that are well beyond what is standard in the substrate trade-and in many cases, the skill of the trade person or the ability of the products and equipment used. The tile industry’s flatness recommendation of 1/4” in 10’ has been embraced by the wood and cement trade organizations. Still, unless specific requirements are established prior to construction and properly implemented, it is safe to assume there will be prep work required when using almost all products larger than 12 by 12. The method used for preparation should be carefully considered. Attempting to correct out of plane conditions with thinset during the installation process is very labor intensive. An unsatisfactory installation is often the result. Floor filling underlayment products, self levelers, or even mortar beds may be required to achieve satisfactory flatness tolerances needed for large tile.
The next big challenge: selecting the appropriate bonding material. This is where we can easily avoid problems. Picking the right thinset need not be a daunting task but you must consider both the site conditions and end-use. If you are fortunate enough to work on a flat surface, you may want to consider a contact mortar. They are designed to trowel smoothly and flow when under the tile to achieve coverage. With very large tile or when working in an area that 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 (one 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. This brings fractures in softer tile and stone and leads to bond loss on dense tile such as porcelain.
Next comes selecting our metering device-which of course, is more commonly known as a “trowel.” For many years the acceptable thinbed method of installing large unit tile (that is, anything over an 8 by 8) was to trowel the floor and back-butter each piece of tile. This has been industry recommendation for years and remains a sound method for installing large tile. In the mid 1990s research by the National Tile Contractors Association found that there are certain advantages to using a U-notch trowel. Use it to comb all the ridges in the same direction, then place the tile perpendicular to the ridges with a back and forth motion. NTCA demonstrated that this achieved the needed coverage without back buttering.
Talk to any old time installer and you will get some argument here. Yes, applying thinset to the back of the tile is a good thing but it’s also very time consuming in today’s competitive environment. Research continues on ways to achieve good coverage with minimal effort. Tool manufacturers have also stepped up their efforts in this area. Several have come up with some odd-looking notch configurations that yield amazing differences in coverage compared to more conventional trowels. Personally, I have found these tools to be the simplest way yet to achieve good coverage under the tile. Whatever your choice of methods, there is no right or wrong as long as you can assure that there is good complete coverage under the tile.
If such variations in the substrate exist, wider grouts between 1/8” to 1/4” will be necessary to hide the transition from one tile to another. If uniform grout joint appropriate to the condition of the substrate is not used, lippage of the tile will occur. Lippage is a condition where one edge of a tile is higher than adjacent tiles. This gives the finished surface an uneven appearance and can even become a trip hazard. Also, it is not a good idea to have movement joints long with tight joints. A 1/4” joint in the tile work every 10’ to 20’ is aesthetically unacceptable. Still, the consequence of no moment joints in tile work will in all likelihood be failure at some point. It could be a year; it may not be for 50 years, as a recent caller found out. All structures move, all tile moves, so if you know it’s going to move, plan for it.