6 months after we hired someone from Craig's List to do the tile in our shower, one of the bottom tiles started coming loose
After pulling the tile out, I found out that he has just used silicone to keep the tiles in.
I chipped out all of the grout with a screw driver
And scraped off all of the silicone from the tile
And then scraped off all of the silicone from the wall
This is the thinset I had leftover from a different project.
Follow the directions and mix up how much you need
I'm applying a more than liberal amount as the tile was further out as its had all that silicone back there
Replace the tile, use spacers if needed
Once the thinset drys, time to grout
Mix according to the dorections
Cover the seams, according to the directions
Clean up and you're good to go. If you do contact someone to do work in your house, get references and remember, if they're the cheapest, it's most likely, for a reason.