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What are these chimney breast marks?

Evening all,

Can someone please help me? Here’s a picture of my sister’s chimney breast:

You see those 3 marks on the top left of it, any ideas what they are?

She says, “There are three stains in all - the largest (the middle one) is approx. 230mm wide. They’re on the wall - that’s a chimney breast that has three vented pots for three fireplaces, none of which are in use (probably last used decades ago!). The old plaster (original lath and plaster, possibly 100 years old) was taken off and the wall plaster-boarded and skimmed in January so it was very definitely dry by the time I got round to painting it in August (!). It has two coats of bare plaster emulsion on it. The stains came through in a matter of days. They don’t feel any different to the rest of the wall - not colder or damper.”

I’m thinking some kind of soot/damp mixture from badly flashed chimneys… So: check for exterior damage, get if fixed, cut a section of plasterboard out, let it all dry well, seal it with some sort of chemical sealer (advice please…) fill with nicely shaped plasterboard, fill and joint the cracks properly, problem solving primer, repaint.

Does anyone have any other guesses?has anyone seen those stains before?

Thanks in advance,

Dave and Dave’s sister…

Hi Dave.
I have just decorated my lounge with emulsion paint. It was papered before so I thoroughly sanded the walls prior to painting and would you believe it, I have just discovered a small round mark about 120mm in diameter over the chimney breast. I am about to have my flue swept so I will see if that makes a difference thinking that maybe there is either a soot ball or something resting in the flue. For the record the flue has a great draught so I do not think it is condensation. If it fails I think I will apply some zinsser and overpaint. I’m afraid it does not resolve your problem at the moment but it may give you some thoughts.

I feel your pain! Thanks for getting back to me, good idea to get the chimney swept, if it’s blocked I guess that would be a symptom.

Hi Dave
Today I had the chimney swept and asked the guy about the mark on my chimney breast and he said it could be a blockage of some sort or an old bird’s nest or condensation due to a lack of air movement or draft in the flue. In my case it was neither of these so I shall monitor the patch and see if it goes and if not revert to the Zinsser option.
Best of luck.

Thanks for letting me know. The air movement thing rings a bell with an old chimney problem I had a longish while ago.