I finally decided to get around to replacing a soap dish wall tile in the bathroom (the dish itself was half broken off, and a different color than the surrounding tile). Naturally, this has gotten more complicated than I would have liked.
Turns out the the soap dish tile was about twice as thick as the rest of the wall tile. As a result I had to take out an adjacent tile to remove the soap dish tile (not a big deal).
Now I have two tiles to replace, only one of the spaces is about a half inch deeper than the other.
For the deeper space, how should I get the surface level? Can I use thinset to build it up level, let it cure, and use thinset again to bond the tile? Or is there some other sort of plaster compound? Or can I get away with just using a lost of thinset all at once when I replace the tile?
I'd use thinset to fill the deep part and let it dry. Then tile the area. Set the tile dry in the left side to see what sort of space you have for the adhesive. The tile needs to float on thinset, so you need at least 1/8" more depth. Less then that, I'd use construction adhesive.
Is this inside a shower? If so - no construction adhesive.
If you try to first fill the depression with thinset the thinset will sag terribly. I think I would use thinset but gob-on enough to fill the depression and let it ooze as you place the dish. Once the dish is in place remove what oozing thinset you can for now. Use duct tape to hold the dish in place. After about twelve hours gently remove the duct tape and carve out the remaining and offending thinset. Then in another twelve hours a wet sponge will clean up the rest of the mess. Thinset just never stays in place on a wall when trying to fill a hole.