From my experience, no you dont have to remove all the old mastic, as long as it is still bonded to your subfloor. Unless it is loose or peeling it can be left there. : Is this considered pumbing related? Anyway, I am about to lay some tile. I took up all the old squares and there is a glue residue on the floor. Before I lay the new tile, do I need to get this up, or can I pour the new glue over it?
