I've been doing temporary patch repairs by cleaning off the backs of the tiles, vacuuming up the dust, and re-laying them in wallboard compound.
I guess I'm going to have to tear the whole mess out, put down a sheet underlayment, and set the new tiles in mastic.. The hard part will be getting the height set so they mate with the wall edge trim and the toilet flange.
I don't understand what advantage bedding the tiles in mortar is supposed to have, when the floor underneath is going to flex. I suppose it might work on a slab, but not on wood. -- Email reply: please remove one letter from each side of "@" Spammers are Scammers. Exterminate them.