Install Tile on Tile?

And it can be done, though it’s not the optimal tile-laying base.  Why?

The main issue is glossiness.  Most tile has glazing; that’s why we install tile, after all.  Glazing repels water.  Glazing also repels thin-set mortar, the stuff you’ll be using to lay down your next layer of tile.

The work-around is to roughen up your existing tile with a belt sander.  Put some heavy-duty grit sandpaper in the 40 to 60 grit range, on your belt sander.  Slip on a pair of safety glasses.  Seal up doorways to prevent tile dust and particles from invading the rest of your house.

End up cracking a few tiles?  Don’t worry; no need to repair.  Your next tile layer will cover everything.

Let the weight of the sander and weight of your hands do the work.  Don’t press hard.  You probably won’t be able to get every single square inch of the tiles, but don’t worry.  Just get most of it.

After sanding, clean the tile surface thoroughly–clean enough for a baby to crawl on.

Then install tile on tile, just as if it were any other type of underlayment.