A buckling or partly raised tile on your shower wall usually means water has gotten behind the tile—often through cracks in the grout—and caused the wall material to expand, pushing the tile outward. This is one of those problems that feeds on itself, getting worse if you put off the repair, because the buckled tile allows more water to get behind adjacent tiles. The solution is to extract and re-set the tile, or put a replacement tile in its place if the existing tile has been damaged by the buckling.
Things You'll Need
Grout saw (square carbide blade with a handle)
Replacement tile, if necessary
Scrape the grout out from around the buckled tile with your grout saw by rubbing the blade back and forth over the surface. Dig down gradually, taking care not to damage the surrounding tile or the wallboard behind the tiles.
Position your chisel so the tip is sitting in the grout line on the edge of the tile, at its base. Gently hit the chisel with a hammer, loosening as much of the mortar as possible. If the tile isn't broken, try not to break it. Chisel around all sides of the tile repeatedly until it comes out. Clean up the wall with your chisel.
Use your putty knife to spread tile mortar on the back side of the tile (either a replacement tile, if necessary, or the original tile, if it's salvageable). Set the tile in place, spacing it evenly with the tiles around it. Let the mortar dry for 24 hours.
Grout the space around the tile, pressing grout into it with your grout trowel. Wipe the excess grout off with a damp sponge. Let the grout cure for three to four days. Don't use the shower during this time.
Apply grout sealant over the new grout lines, painting on a thin layer of it over the grout surface.
Use protective eye goggles while digging out the old grout.