can you lay ceramic tile over existing ceramic floor?

Depends on many different factors including size of area to be re-tiled, the condition of the floor you're replacing, and the number of doors, fixtures, and flooring transitions you have to deal with. If the existing ceramic is on a cement slab or on backer board I suggest you chisel up the existing tile and re-tile over the slab, especially if any of the tiles are loose or badly cracked. Renting an impact hammer would help a great deal. If the old floor was laid directly on the plywood subfloor tearing up the floor will be a mess and you'll probably have to put an underlayment of thin backer board down over the mauled plywood. If the old floor is on a plywood underlayment you can probably tear up the plywood with relative ease. Tiling over the old ceramic is possible but will add height to the floor thereby complicating doors and flooring transitions. I've seen contractors just spread thinset over the existing tile and re lay the floor. This wouldn't be my choice for most jobs. I ...  more