Thank you - most of the chalky stuff is off but there are a few resistent bits left so bit of extra security is great. I bought some of the WBA today - the instructions say 2-4 hours to dry. Is leaving this overnight too long or should it be fine? Will have a chat with the guys tomorrow and suggest the wba but i know they were keen on stabilex. I can promise you they are good guys, and the plasterer they got in was nice as well, I think they just got caught out with the mishap before and they applied pva before the plasterer had seen the walls so he didnt recognise the chalk when he came to plaster. Theyre doing everything they can to put right so all this extra advice is helping hugely thank you. If nothing else it had given me an understanding of what went wrong, and never know when ill come across this stuff again!