Mold on the wall

Hello,
I have a question. We rented an apartment that was still fully wallpapered. Now that we have removed the wallpaper, we had to find mold all over the walls in the bedroom and kitchen. We informed our landlord and he said that it was only the backing paper but there could not be mold in the plaster because the plaster has a pH value where mold cannot survive or form. He then advised us to remove the stains with a [Reißbreit] (no idea if that is correct) and then replaster. Now we are, of course, worried because it is the exterior walls that have mold. Could the problem perhaps be deeper?
We have two small children and are very concerned because of that.
I hope you can help us.
Thanks in advance.
Kathleen :)

Hello Kathleen !!!
Well, I would say it's a difficult case because the problem is that you would need to see it on site.
What does the mold approximately look like ??
It could maybe be that the old wallpaper was not breathable and therefore sealed off the wall.
Whether the problem might lie deeper, well, there are a few indications: Is the exterior facade discolored at the spot where you have your mold, or does a gutter run down there, or are there drainpipes or even a water connection (pipes) in the wall in the room itself.
The best thing would be to remove the disposable wallpaper to see if the substrate is also affected. If that is the case, then I would say to chip off all the plaster and replaster.
I hope I could help
Best regards. ;)

Hello Jackal Thank you for your answer. Yes, the wallpaper could be a good explanation because there were partly 3-4 layers. And the mold was partly on the last layer or underneath directly on the wall. I would first have to check the gutter. We have now removed the mold and replastered the surface. I hope the problem is solved now. Thanks again. Best regards Kathleen

Hello Kathleen!! Well, it could really be that mold has formed because of the many layers of wallpaper. Well then, I wish you that your apartment remains an oasis and that no further mold formations occur. Best regards ;)

Hello, I have a question. We rented an apartment that was still fully wallpapered. Now we have removed the wallpaper and had to find that the walls in the bedroom and kitchen are full of mold. We informed our landlord and he said that was only the backing paper but mold in the plaster could not be, because the plaster has a pH value where no mold can survive or form. He then advised us to remove the spots with a scraper (no idea if that is correct) and then re-plaster. Now of course we are worried because it is the exterior walls that have the mold. Could the problem perhaps lie deeper? We have two small children and are very worried because of that. I hope you can help us. Thanks in advance. Kathleen :)

Are they ONLY the exterior walls? Is there nothing on other spots where there was wallpaper before? That sounds at least suspicious.

I also have mold problems and sprayed an anti-mold agent with active chlorine in the bathroom, which worked great, and then I treated it with an anti-mold agent. I think the stuff was from Wepos... Since then, hardly any mold in the bathroom.

Does the entire plaster really have to come off?

Best regards