Why Wall Tiles Fall Off Walls
DEAR TIM: The 8-inch by 10-inch wall tiles in my bathroom are bulging out in places. I pushed on them and they moved. Further investigation revealed many are loose and only held in place by the grout between the tiles. The tile have been up for eight years installed by a pro who supplied the adhesive. What might be the cause for this problem? I believe I can salvage the tile. How can I permanently adhere my salvaged tile to the wall? Lloyd May, Sydney, New South Wales, Australia
DEAR LLOYD: I'm sorry to hear about your dilemma. I've had the same thing happen to me many years ago when I was just getting started in construction. It only took eight days for my tile job to fail, not eight years! It was the first and last time I had a problem with tile failing.
As each day passes, I'm afraid young contractors and tile setters become more detached from the tile setting methods of old. I have vivid memories of using a sledge hammer to remove ceramic tile from a wall. It was cemented, yes - real cement - to a bed of cement mortar that was installed over metal lath. That tile, had I not beat it to death with the hammer, would have stayed on the wall for centuries.
New time and cost-saving methods often push aside time-tested techniques used by the master tile setters of old. Fortunately there's a compromise you can choose allowing you to reinstall your tile so it will not fail.
Let's first discuss the possible reasons for failure. I can see from your photos the installer used an organic mastic on your wall. This glue resembles warm cake icing and is usually water-based. It's not a bad product and can have strong adhesion if you just follow the use instructions.
The biggest mistake many make when using an organic mastic is allowing it to skin over. This happens if you expose the mastic to air for too much time 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 water evaporating from the mastic causes the mastic to stick to itself. The best example I can offer is a piece of fresh adhesive tape that gets coated with dust. The tape is no longer sticky.
The mastic could have been defective, although I would say this is a low probability. The tile setter could have used the wrong sized notched trowel. The instructions that come with the tile or mastic tell you what size trowel to use for each sized tile. Bigger tile need a larger notched trowel.
The wall surface or backs of the tile could have been dusty before the adhesive was applied. Dust and adhesive are bad jujumagumbo. The dust is selfish and steals all the adhesive for itself.
The wall surface could have been irregular with humps and dips in it. I feel this, in conjunction with skinned-over adhesive, is the root cause of your tile failure. As ceramic tile get larger, the wall or floor surface must be flatter and flatter. Since 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. This is why my tile job failed all those years ago. When I pulled my tile of the wall, you could clearly see bare spots on the tile where no adhesive even touched the tile.
I'm glad you're able to salvage the tile. Your job now is to 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.
It's now time for the hard part. You may be able to scrape off any mastic from your walls using the same method. You'll have to spritz the mastic on the wall with water from a spray bottle. You may discover using a paste paint stripper is an easier way to soften the adhesive as paint is nothing more than colored glue.
Once the mastic is off the wall, it's time to use a straightedge to determine if the wall surface is perfectly flat. If there are low spots and humps, you need to skim coat the wall with cement-based thinset to get the wall surface flat and in the same plane. Thinset is a blend of fine silica sand and Portland cement. It's imperative the wall is dust-free and slightly damp when you apply the thinset. You want the thinset to bond very well to the existing wall surface.
You'll use the same thinset to adhere the tile to the wall. Do what the master tile setters did nearly one hundred years ago. Install the tile the day after you flatten the wall with the thinset. The microscopic crystals of the hydrating cement in the thinset already on the wall will interlock with the fresh thinset you trowel onto the wall creating a lasting bond.
Only apply as much thinset on the wall as you can cover with tile in five minutes. Use cold water to mix the thinset to retard the setting time. Do NOT add water to the thinset if it starts to get hard in the bucket before you spread it. Only mix enough thinset as you can use in one hour or less.
Use the correct notched trowel to apply the thinset. Visit a real tile store and obtain written instructions for a similar sized tile. See what size trowel they recommend.