We did it as a do-it-yourself project to our tiled shower ten years ago this year. Good idea; if it does not leak now, then it should not leak after the retiling. The only dicey part was at the drain, where we sloped the new tile to avoid expensive extension of the existing drain pipe fittings.

All around bad idea for in a shower... This process is different if it is over a regular floor.

Todd Stull
Enola, PA