Dr. Schmidt explains the world: Why does the wallpaper get moldy?

Steffen, I discovered mold on one of the outside walls in my bedroom. Why is the wallpaper moldy there?

You said an important word: exterior wall. I assume it is a building with rather moderately good thermal insulation on the outside walls.

The building was built quickly after reunification. So yes.

So that the outside walls become really cool in winter.

Correct.

If there are several people in a room like this, they breathe out water vapor, which then condenses on cool walls. And by doing so, you’re giving fungal spores, which are almost everywhere in the air, a good opportunity to colonize. And the wallpaper is made of several materials: from the cellulose in the paper to the glue in the distemper and the glue under the wallpaper. All things that mold likes.

If my wall were well insulated, the condensation wouldn’t stick to it. Say: I wouldn’t have any mold?

You probably don’t heat much in your bedroom?

Races.

You see. This additionally cools the wall.

Is mold on walls dangerous?

Only if one of you has an allergy to the relevant type of mold or if one of you has a weakened immune system. If neither is the case, the danger is manageable.

Does ventilation help against mold infestation?

Ventilation is important after showering, where large amounts of condensation form. Then the steam can escape easily. However, there are also rooms without windows. And is the ventilation always effective? That’s why there’s nothing wrong with properly insulating the walls. How did you combat your mold?

I cut the wallpaper a little with the cutter, peeled off the affected part and treated the wall with chlorine spray. Was that right? Or should I have used something else?

You’ve definitely solved the problem right then and there. And if you’re careful not to inhale too much of the spray, it’s certainly okay. Otherwise, such aggressive agents are of course not without danger

What can I use instead? Vinegar?

Vinegar would only superficially solve the problem. Because with mold it is like with all other fungi: you only see a fraction of the entire living organism. Most of it is in or under the wallpaper. You can wipe as much as you want with alcohol, hydrogen peroxide or acetone. Removing and disposing of the wallpaper is probably the safest thing you can do.

I have another problem in the bedroom: my windows. They “sweat” so much in winter that you have to wipe them dry in the morning.

I suspect that the insulating glass in your windows is no longer tight. Modern windows have two to three panes of glass with a cavity in between. Unlike traditional double windows, there is an inert gas in the cavity between the panes as thermal insulation. If this escapes through a leaky connection between the panes, the thermal insulation of the windows is significantly lower. In other words: the windows are cold when it’s cold outside. And then the exhaled water vapor condenses on the window panes. Like on the wallpaper.