Tile over Tile?

I have tile in my bathroom walls and floor. Is their a way to put tile over tile. I know if I chisel the tile off, the glue is left on the plaster walls and I was told the only option is to cut out the wall and tile over the tile floor. thanks T.C

It can be done, but the tile has to be abraded with a carbide-grit sandpaper. An epoxy mastic should be used. Be absolutely certain that the old tile is sound, and that no additional waterproofing membrane is required.

Dannie