Plumber is boxing in pipes in my bathroom using plasterboard (gyproc?). He says I can put a primer on and then paint directly. Is this true? I thought I'd need to get them skimmed. If not, do I need to do anything special to the plasterboard before painting it. I would obviously use a primer, but I'm wondering if I have to do anything special to joins, etc in the board? Also, as the boxing in will adjoin an already plastered wall, is there anything special I should do along these joins, or can I just use some caulk to fill in the gaps? Thanks.