concrete floor.

This is obviously a stupid question because i am obviously a novice. But do i have to lay plywood over my concrete floor in the bathroom? Or can i lay the ceramic tile on that concrete floor.

Also, the concrete floor has been painted and sealed with a polyurethane coating. Would it be best to remove that polyurethane coating??? Thanks

Hi,
Plywood is only used to line timber subfloors and protect the ceramic tiles from the movement which always occurs on timber floors. There is no reason to line a concrete floor with plywood (unless you want to raise the height of the floor by a substantial amount).
The only preparation required should be the application of a latex based levelling compoubd to smooth out the floor.
If the existing coating is blistered or soft then it should be scraped and removed. If it is sound then you should be fine but I would still apply a wash latex screed to provide a clean, new surface for the tiles to be laid on.
Jim.