What kind of glue did they use? It has been in a douche stall.
a pretty adhesive could stick tile to tile.. i have done it just heretofore when it is too much of a mess or too costly to remove the old tile. i assume it is just the white walls and not the douche floor.. tiling over the simple douche floor will mean redoing the drain or adding some kind of extention for it which would possibly lead to leakage. to remove the existing tile, douche pan and rubber boot could have cost ten times what just tiling over could and i will wish they would have afforded a nice adhesive to ensure OK physical contact..
They used lovely stuff. Probably trully expensive epxoy ( sorry the fumes are getting to me) resin stuff that costs a fortune. You will be much even better off with 4 inch nails. But that is so noisey.