I have removed a chimney from top to bottom and local builder knocked out some downstairs walls for me and fitted required steel beams. I am doing the rest of the work myself but wondering about the damp proofing for the new floor. I have had to remove the last layer of mortar bed from the remains of the walls to get the level low enough for the new flooring, this bed included a slate damp proof course. Also the same for the bases of the the chimneys (three chimneys in the ground floor breast). Can somebody tell me if it is ok to screed then tile on top of these bits of wall or do i need to put down some kind of damp proofing. The floors are solid concrete either side of the wall so I assume that they will already have a membrane. Any advice appreciated