We recently pulled up the vinyl in our bathroom to discover that there is backerboard underneath. It is in good shape but has a thin layer of glue on parts. The surface is completely smooth. Can I install tile on this existing backerboard, or do I need to replace the backerboard?
If it's in good shape (clean, planar, etc.), then it is fine to put tile on top of it, assuming that putting tile on it doesn't make the floor too high at the entrance to the bathroom.