A tile repair job prompted me to post this. There are many factors that influence the quality of a tile installation. While I can’t possibly include all the information in this post, I will attempt to touch on the mastic vs thinset.
There are basically two types of “glue” used to install tile, thinset and mastic. There are even different types of each of those, but we don’t need to get into those details for this discussion. Simply, thinset will offer the widest variety of acceptable installations. Mastic has definite limitations and IF you’re going to use it there’s really only one place….applying wall tile in dry locations. Mastic should never be used in wet locations like showers and tubs. Mastic should also never be used for floor tile. Mastic will re-emulsify in wet locations leading to loose tiles, cracked grout, and the need to have the tile replaced. Thinset is the only thing that should be used for installing tile on floors, and in other wet locations. Grout is not waterproof and will allow a certain amount of moisture to pass through to the substrate and this moisture will not negatively affect thinset the way it will make a mastic tile job fail. Some grouts are better than others for water resistance but none will be water proof.
The above pictures are of a failed tile shower installation. The contractor put a lot of time and effort into creating the custom mud shower bed, removed an alcove wall to create an open view shower with bench, and nice custom glass enclosure. While the tile work didn’t have the best attention to detail like field tile edges exposed at corners instead of bullnose tile or radius trim strips, the biggest mistake was the use of mastic to install the tile. What really lacked common sense is that the walls were installed with thinset, and just the shower floor (the absolute wettest location possible) was installed with mastic. This shower was not used for at least a month after the tile was installed waiting on the custom enclosure to be made and installed. This was more than enough time for the glues and grout to dry and cure thoroughly, yet…..after just several weeks of using the shower the floor tiles were already becoming loose and “smushy” underfoot. The mastic was turning back to it’s liquid state from the water, and seeping up through the grout that was now cracking due to the loose tiles.
In this instance at least the repair was limited to just the shower floor rather than a complete removal and rebuild. It was stripped to the mud bed and even a couple wall tiles were removed to verify how those were installed. I just couldn’t believe that mastic was used on the shower floor, and not everywhere else….but it was true. (Added bonus, it was not sheet rock inside the shower either) So, we dried the mud bed out with a dehumidifier, a fresh liquid waterproof membrane was applied, and new floor tile was installed…with thinset. I’m posting this now since I was recently able to check in on the repairs while doing other unrelated work on the property. Nearly two years since the repair and no recurring problems.