Brown stains appearing on bedroom wall

Hi guys,

Hope you can help me suss out what's going on here. About 3 years ago we had our bedroom walls skimmed, we painted, no apparent problems. As of a few months back we noticed brown spots starting to appear on one of the walls. We're in a first floor flat, it's the wall between us and the outside world ( ), I believe it at one point long ago must have been a fireplace. We painted the plaster first of all with a good coat of white emulsion, then with a bog standard BQ interior matt.

The stains are light brown, range in size from several smaller ones 2" x 2" to a larger fainter stain around 6" x 10", they won't wipe off, there's no particulate matter on the surface. Any ideas what this is and the best way to go about getting shot of it?

Incidently, prior to the skimming the walls were papered, I removed the paper and don't recall seeing anything amiss on the plaster underneath.

Thanks

is there a chimney on the other side of this wall?

I believe there is a chimney yes, although it's been out of use since before we bought the place some 15 years or so ago. As I said above, there were no similar marks on the original plaster, however there was the dreaded woodchip on top so that might have prevented a similar issue before.

Thanks again for the help.

it is likely that there is damp in the chimney and it is bringing soot-stains as it soaks through the wall. Once this happens it is very difficult to stop and you will have to use a stain blocker.

You also need to get that chimney ventilated, and make sure it is not allowing much rain in through the top or by bad brickwork.

If the old fireplace is in your room you can make a hole where it was bricked up and put in an airbrick. There may be more than one flue in the chimney (e.g. one from upstairs fireplace and one from downstairs fireplace) and they both need ventilating.

As well as the stains, this will also stop damp.