On a wall you usually can, if the existing tile is solidly bonded and you use the right primer and mortar. On a shower you should not, because it buries whatever is failing behind it and raises the floor in ways that break the drain and the door.
The honest version
Tiling over tile is a legitimate technique and it is also the single most common way people spend real money burying a problem. Whether it is a good idea depends almost entirely on where.
Where it works
A dry wall — a backsplash, a half-height wainscot, a floor in a powder room — where the existing tile is sound. Test by tapping every tile with the handle of a screwdriver. A solid tick is bonded. A hollow knock is not, and any hollow tile has to come off. If more than a few are loose, the whole field is suspect.
You need an epoxy or a modified thin-set rated for tile-over-tile, and usually a bonding primer. The existing glaze has to be scuffed and scrupulously degreased. Skipping either step is how it fails in a year.
Where it does not
Inside a shower. Three reasons, and all of them cost money later:
- You cannot see the waterproofing. If the reason you are re-tiling is that something looks wrong, the something is behind the tile. Covering it means it keeps happening in the dark.
- Floor height. Adding half an inch to a shower floor puts the drain below the tile surface and breaks the fall. There is no good fix for that afterwards.
- Weight and thickness. Two layers of tile plus two beds of mortar is real weight on a wall, and it throws out every transition — the door, the curb, the niche, the valve trim depth.
The question to ask yourself
Why are you re-tiling? If the answer is "I do not like the colour" and everything is sound and dry, tiling over on a dry wall is reasonable. If the answer is "there is a stain, a soft spot, a smell, or grout that keeps cracking", you have a water problem, and tiling over a water problem is the most expensive thing you can do with a weekend.
What a tear-out actually involves
Less than people fear on a wall, more than people hope in a shower. A shower tear-out down to studs, new waterproofing and new tile is where most of the $15,000–$28,000 full-bath range goes. It is also the part that determines whether the room lasts fifteen years or three.
← All bathroom questions Bathroom remodeling in Pinellas County →