Painting Over Black Waterproof Paint - How to Best Prepare Surface? General decorating topics, questions and answers. find help, tips and advice on completing your decorating projects

[caromary58]

We are removing some wallpaper that is silver backed and peels off very easily. Behind the wallpaper is a black slightly streaky coating, which I assume is over plaster as this used to be an exterior wall before an extension was built. I assume that the black coating is some kind of waterproofing paint. I believe that it would be difficult to paint over this - what do I need to do to prepare the surface for paint? NB I am a very amateur decorater but want to do this myself.

Many thanks!

[caromary58]

I'm sorry but I can't work out how to edit my post. I wanted to give a bit more information about the black coating under the wallpaper that I need to paint over.

It is waxy and streaky in appearance, and when I rub it the black comes off on my finger, which confirms that I couldn't paint over it. The fact that the wallpaper comes off so easily makes me concerned that lining paper wouldn't stick well. Does anyone have any idea what this is and how we can cover it?

[proptech]

Hi caromary58

I can't think of any type of coating this can be. As it comes off on your finger, what happens if you give it a good scrub with water ? It may be that it can be washed off with Sugar Soap. The other thing to try is to wet it with white spirit, just a small area to test. That my give us an idea what we're dealing with.
Please get back and let's know.

[ChrisKia]

Sounds like tar or bitumen! ^^
Try to remove it with thinner.