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.
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.
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?
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."