I've just had ceramic tiles laid on top of wooden floorboards in my bathroom. The tiler said that the boards were level and there was no need to screw them down or cover them. He laid the tiles directly onto the boards. I've since been told that they will probably lift and crack. Is this so? If so? How long would it take for this to happen and if it does, will it be possible to take the tiles up to re-do the floor properly without breaking them and will I be able to remove the adhesive/grout? Help!