I removed the existing tiles that were on my kitchen backsplash and I am planning on putting on new tiles. When I removed the old tiles, the drywall was damaged- no holes but areas where the cardboard paper came loose a bit, peeled, etc.. There is old glue also there and some plaster/tape. Do I need to replace this drywall and put up a new board or can I sand the glued areas and apply compound and/or a coating to repair the loose paper before gluing down the new tiles.