What is this paper/foil layer I'm destroying?

[fozzie52]

My bathroom has a damp wall from where the roof was leaking that (I think) I've cured. The bathroom is a lean-to extension built off the back of the house, and where the roof met the wall there was a big gap. The wall pictured would have been an exterior wall originally.

I'm now attacking the interior and have been scraping away at the damp paint. The wall has been plastered and has a paper/foil layer behind the paint that is damp and moldy and I've been pulling it off. I assume its some sort of vapor moisture barrier? Should I put something back and if so whats it called?

Thanks,
Ben

 

[freddiemercurystwin]

Its probably a foil faced bitumen membrane, used to stick over damp walls, then you can paint or wallpaper over it, a bodge to avoid fixing a damp problem but can be effective in some cases. This is the modern version: https://coveryourwall.co.uk/products/wallrock-dampstop-thermic If you're confident you've cured your water ingress problems then there's no need to reapply it ....

 

[fozzie52]

Ahh. Ok thanks,

The house is very old, and doesn't have a damp course. Do you think it's to help against that? (But there must be three/four foot of tile below it as well so seems odd to me.)