Key mortar into suitable substrate to receive ceramic tile or stone with the flat side of the trowel.

There are many reasons why ceramic tile installations fail. At our office in Jackson, Mississippi, we receive numerous technical calls a day related to job problems. In an industry growing by leaps and bounds, nothing concerns us more than failed tile installations. At the National Tile Contractors Association, one of our main goals is to provide education and training in an effort to minimize job failures. To accomplish this goal, our staff documents these calls in an effort to identify trends that may contribute to jobs that are failing.

Comb-in one direction-with notched side of properly selected trowel.

By far the most glaring issue we come across is the lack of adequate thinset coverage. Failing to achieve industry required thinset coverage is a request for trouble for tile setters. Even if other factors contribute to installation failure, lack of adequate thinset coverage will more than likely cost you money. Your best defense against this situation is simply to not allow it to happen.

The American National Standard Specifications for the installation of ceramic tile (ANSI A 108.5) defines allowable coverage as: Average uniform contact area shall be not less than 80 percent except on exterior or shower installations where contact area shall be 95 percent when no less than three tiles or tile assemblies are removed for inspection. The 80 to 95 percent coverage shall be sufficiently distributed to give full support to the tile with particular attention to this support under all corners of the tile.

Firmly press tiles into mortar and move perpendicular across the ridges approximately 1/8-to 1/4-inch.

The term coverage in this scenario applies to the amount of adhesive remaining on the back of the tile once it is removed for inspection. This must be a minimum of 3/32-inch thick for the thinset to perform properly.

If you or your employees fail to comply to this specification, it will not matter if other factors contribute to a failed installation. You will be deemed responsible because of your failure to accomplish this step. It is that simple.

Pressing firmly, move back in the opposite direction 1/8-to 1/4-inch to flatten ridges into the valleys, removing air from between the mortar and tiles.

Without naming names, I know of numerous situations where this scenario has played itself out to the demise of the tile contractor. Cracks in the substrate, excessive movement, failure to install expansion joints etc. can and have contributed to job failures for ceramic tile. However, if a manufacturer, architect or consultant discovers a lack of adequate thinset coverage, the focus of the problem will shift back to the tilesetter.

What are some of the things that can go wrong when we don’t take the time to ensure we are getting proper coverage? In the photo on page 38, there is no thinset visible at all in sections of the substrate where the ceramic tile has been set. Imagine the hollow sound one might hear on this floor. Undoubtedly, the corners of this tile will crack, the grout will probably crack or pop out of the area in chunks, and one of the corners of the tiles will probably raise up, causing chipped edges, unacceptable lippage and a tripping hazard. Sounds like a lot of fun for those who worked on this job, doesn’t it?

This method can produce specified coverage with the corners and edges fully supported, without backbuttering or beat-in.

To achieve maximum coverage, it is first necessary to select the proper size trowel for the installation. A trowel is a gauge, and its depth will determine the amount of adhesive spread. For most 8-by-8-inch-and 12-by-12-inch-tiles, a 1/4-by-1/4-by-3/8-inch trowel is recommended. Some of today’s tiles come a trifle thicker than the norm and may require a deeper gauge, perhaps 1/2-inch in depth.

Of vital importance to achieving maximum coverage, especially in large size tile installations, is the method in which the adhesive is spread. The NTCA has produced a video called “Trowel and Error,” which demonstrates this money saving technique in just a few short minutes.

The five pictures on the left depict the proper method for spreading the adhesive. After properly setting the tile into the adhesive bed, periodically remove some pieces and check the back to assure proper coverage is being attained.

By following these guidelines, you will go a long way towards eliminating some potentially devastating situations to your financial bottom line. This way, when a problem on your job does arise, what a great feeling it will be to hear the manufacturer’s representative say, “Well, we can eliminate coverage being the problem because this was installed the right way.”