On Aug 7, 8:17 pm, "D'Olier" wrote:
What do I need to tile an upstairs bathroom? I know you shouldn't tile
directly onto the plywood. I've heard you need another sheet of plywood and
then some mortar/backer?? board but then the floor will be about an inch
higher than the hall floor.

If you do determine that you have flexing, and you cannot fully
eliminate that flexing (for whatever reason). Then you should use
smaller tiles on the floor like 6x6. The larger the tiles you use,
the harder your subfloor needs to be. Women dont like to hear that
because the big tiles have been in vogue for a while now, but maybe
you can appease her by putting big tiles on the walls and small on the
floor. If you can get a good solid floor then use thinset for setting
the large floor tiles not mastic. Mastic or thinset is ok for the
walls though.