Painting over bitumen paper

Biggles

The room I'm now decorating hasn't been done for some time and last time I papered it. This time, I've been asked to emulsion it.

Most of the paper is stripping off easily but, round the bay window, I found a layer of black-surfaced paper under a thin layer of silver foil.

I'm assuming this was an attempt to damp-proof the bay, much of which is wood and plaster, not brick, and tends to take the brunt of windy and rainy weather. In fact, for some time, the top paper has been peeling off alongside and behind the CH rad right under the window.

The silver foil is beginning to strip off as the wallpaper comes off, so it'll all have to be removed, but the black-surfaced paper, which appears to be bitumen paper, is a tougher proposition. Does anyone have an idea how well it might take emulsion if I decided to leave it on?

Biggles

Bumped and clarified, now that I know I am dealing with bitumen paper.

TheCyclingProgrammer

It seems strange to have bitumen paper on the inside of the wall as I would have thought this would form a waterproof layer on the outside skin, between the rendered or tiled finish and the internal stud work.

Either way I wouldn't have thought it would take paint. Could you rip the plaster off the inside of the bay, back to the bare stud work, then re-line with plasterboard and have it skimmed? Its only a small area so shouldn't cost a fortune.

You could potentially look at insulating the bay at the same time although beware this could be a bit of a rabbit hole depending on how the outside is sheathed as the you need to start thinking about interstitial condensation and making sure the frame can breathe.

But even if you didn't insulate, a freshly plasterboarded and skimmed internal lining will give you a good base for decorating.

Biggles

Apparently it was quite common, some years ago, to line walls with this, presumably to protect the finish on the wall.

I have read that the bitumen would leach into oil paint, but did see a suggestion that emulsion would be OK. I'm hoping someone may have experience of it.