Loose tiles can be salvaged
Tim Carter Ask the Builder
LLOYD MAY These tiles had poor adhesion to the wall. The reasons for failure are many.
Q: The 8-by-10-inch wall tiles in my bathroom are bulging in places. Many are loose and held in place only by the grout.
The tile has been up for eight years, installed by a professional. What might be the cause for this problem?
A: I can see from your photo that the installer used an organic mastic on your wall.
The biggest mistake that many people make when using organic mastic is allowing it to skin over. This happens if you expose the mastic to air for too long before you press the tile into the adhesive. When a skin develops on the mastic, the adhesive doesn’t offer much of a mechanical bond to the tile.
The mastic could have been defective, although I would say that’s a low probability. The tile setter could have used the wrong trowel. The instructions that come with the tile or mastic tell you what size trowel to use for each size of tile. Bigger tile needs a larger trowel.
The wall surface or backs of the tile could have been dusty before the adhesive was applied.
The wall surface could have been irregular, with humps and dips in it. Because the tile is flat and in the same plane, the wall surface must also be a perfect match. If the wall has humps, the back of the tile will touch the hump and then not contact the wall where there is a dip.
To salvage the tile, remove any organic mastic that is stuck to the tile backing. If you soak the tile in water, the mastic will almost always soften. You can scrape it off with a flat spackling knife or a chisel.
Scrape off any mastic from your walls.
Use a straightedge to determine whether the wall surface is flat. Skim coat the wall with cement-based thinset to get the wall surface flat and in the same plane.
You’ll use the same thinset to adhere the tile to the wall. Install the tile the day after you flatten the wall with the thinset. The interlocking of the thinset crystals will create a durable bond.
Tim Carter is a columnist for Tribune Media Services. He can be reached via his website, http://www.askthebuilder.