I bought some porcelain tiles for my bathroom, only to realise afterwards that they exceed the weight limit for skimmed plasterboard. I have now painstakingly scraped off all the old skim and am left with original plasterboard. Can I now just tile straight onto the plasterboard or do I need to treat it with something first? I have tanked the shower area with BAL WP1 but I assume I dont need to do this for the whole bathroom? I have bought some BAL rapidset flexible adhesive for fixing the tiles. Thanks