TileProf says: |
Hi Catherine, sounds like a Bitumen damp prrof layer, this is horrible to get off the back of the Tiles, you will need machinery and patience to do this, such as a wet Vac, some Remove and Go and Nano-tech cleaner mixed together and left to soak on the back of the Tiles in a tub for a few days, ther is no easy answer to this problem, sorry.
Regards Russell at Tile Doctor |