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bluebob
forgot to add,or take timeless johns advice.either way you should be ok
sorry guys why should you primme the undersurface joke there is no damp there if you guys are looking for advice then look ere
BAL don't specify priming the tiling surface of ply with their adhesives, and as per Alan P for why you prime the underside.prime the surface and edges of the borad use 18 mm ply ,why prime the under side of the board tip wen srewinf down dont use long screws ,they need to be shorter then lenth of the ply and the floor board take my advice you may hit a pips ahesive needs to be flexible I uesd a webber product with AD250 and primer T