HELP!! I have stripped off wallpaper in my daughter's bedroom only to find ancient paint bubbling underneath. I am in the process of stripping this back to plaster as it was painted directly onto the plaster originally. The house was built in the 30's and I believe the plaster is quite old. It apears to have a brown powder under the paint. How do I seal this properly without damaging the plaster - and should I get it skimmed or just seal and paint? I welcome any advice, and thank you.