Mold on wall (chimney)

Dear house-building forum,we have bought a terraced house from the 80s and are now really getting involved with DIY for the first time. That is why I am registering here and asking our first question, or rather describing the problem.

According to the building surveyor, the house had no defects, but now, when moving out, the owner notices that on a wall that faces inward but is the wall of the chimney flue, mold has appeared (for 30 years a wardrobe stood tightly against it). Attached is a picture. We first want to know:
- can I try to fix this myself by removing the wallpaper and putting up new wallpaper?
- and should one then use wallpaper that also insulates, like a thicker one?
- does the wall then need any special treatment, even if it is not damp?

I think as a layman that it should not be a masonry problem in the first floor? There is no water in the chimney flue... In the basement it would probably be worse?

Many thanks in advance for a few tips!
Peter

PS: So far, we have not found any mold on other parts of the chimney flue.

Hello,

According to the building inspector, the house was without defects

What qualifications did this lady have, how did you find her, and what does the report say regarding liability?

Best regards from the Rhineland

Hello Peter,

It also doesn’t say expert report, but "purchase advice" above it.

That is more than annoying ...

Proving to the seller that he knew about it is hardly possible (and he probably really didn’t know, the wardrobe was right in front of it).

To be honest, I am not quite as sure as you are.

After my mother’s death, I took over the parental house. Already upon entering the house, I noticed a slightly "musty" smell, which in my opinion was not due to the house being unoccupied for a few days. Following the smell, I found a damp wall behind a wardrobe on the upper floor. We immediately moved the wardrobe away, removed the moldy wallpaper as well as the mold itself. Our first idea – a leaking chimney duct on the roof side – brought the solution. After we hired a mason to install the sealing, the moisture and smell stopped. By the way, the actual chimney duct is located exactly opposite the formerly damp spot; water finds its own ways.

What I want to express with this is that, from this experience, I can hardly imagine that the owner was not informed about the water intrusion; wardrobe or no wardrobe. Unavoidably, odors arise that do not stop at any barrier.

According to the building inspector, the house was without defects, [...] We would initially only like to know:
- can I try this myself by removing the wallpaper and re-wallpapering?
- and should I then take wallpaper that also insulates, like a thicker one?
- does the wall have to be treated specially, even if it is not damp?

If the actual cause of the water ingress is not found and fixed, the measures mentioned above will hardly do you any good in my opinion. Somewhere – presumably at the roof – water is coming in; you have to find this spot.

Once this has been done, if I were you, I would present the invoice from the graduate engineer as well as from the seller and see what comes of it; especially if the repair involves a major expense. Maybe you are lucky, and it is done with a couple of hundred euros.

Rhenish greetings

Re-taping will not help. The cause must be found. Either water damage or a thermal bridge.

Hello and thanks again for your further tips. Yes, the moisture must be coming from somewhere. I have found out the following: - according to the floor plan, there is a pipe running from the oil heating to the right chimney pipe, the moisture on the wallpaper does not come from the left, so in my opinion it is not caused by the unused pipe. Maybe the very old floor plan is not correct either; by the way, three pipes are drawn there or 3x this black and white box). - on the last chimney sweep invoice (before our time) the flue gas temperature is listed as 198 degrees. According to Google, soot corrosion should hardly be possible at that temperature? - if you should be able to see joints in the horizontal gray areas on the wallpaper: isn't a chimney built with flat bricks and not with such high blocks? The distances between the dark "lines" in the photo are about 30 cm.

So if the unused pipe is not to blame and maybe there is no soot corrosion either, then it must come from the rain. We will see what the chimney sweep says about it – his last visit was less than half a year ago. Leaky covers would have been noticed then. In any case, a little roof on top seems sensible to me.

I hope that by fixing the leak we will soon have a dry chimney, maybe even without masonry work...