Imagine, if you will, a 100 year old house in an Historic Neighborhood with small rooms and myriad renovations over the course of a century's worth of innovations in heating, plumbing, interior design and materials. Now imagine what the bathrooms must have gone through! The floors alone have seen wood, tile, broadloom and more tile upon tile. The last incarnation was a cheap mosaic sheet tile on plywood that featured a large lump from years of shifting.
The first thing we did was remove the old tile and replace the plywood. The joists were still in excellent shape! We found a slate look tile for the base look and added a lattice-work marble "rug" of tile to center the small room and give it depth. (This is an excellent way to save money while still incorporating marble.)