Insulate condominium with moldy corners afterward

Therefore the idea to lower the dew point through additional insulation from the inside

The only idea that will lead to success. In my opinion, you will have to use insulation with calcium silicate boards. What is the point of insulating plaster? You would have to expect 5-10 cm of plaster to get even a somewhat reasonable solution.

Painting with lime or silicate paint would then of course be stipulated as mandatory in the rental agreement.

You are not allowed to do that. The tenant can do whatever they want. You are responsible for providing an unconditionally functioning apartment. Sorry.

I see such obligations more often and they work if the resident is not very particular. With some structural peculiarities, last summer it was concrete canopies, even placing larger furniture against the affected wall was not possible and sometimes the renovating painter prescribes that you must not paint over his calcium silicate boards, etc. Whether one is allowed to set that? I wouldn’t be more papal than the pope.

I see such obligations more often and they work if the resident is not particularly special.

They do work / but are not allowed. And if the tenant doesn't feel like it, as a landlord you get the (justified) rent reduction because the mold is due to construction and not due to ventilation behavior. And then it gets expensive. Too risky for me.

sometimes the renovating painter specifies that you must not paint over his calcium silicate boards

That is different because it is specified by the material. But the OP wants to specify the paint as he pleases on normal (insulation) plaster. P.S. If the mold is due to construction on the exterior wall, you should hold the owners' association accountable. The exterior wall is community property. We had to do that for two apartments last year as well. Two walls were then completely fitted with calcium sulfate insulation boards.

It would be interesting to know if other apartments in the building have similar problems. Have you already spoken with the neighbors above and below you?

Thank you very much for the lively discussion.

The only idea that will lead to the goal. In my opinion, you will not get around insulation with calcium silicate boards. What is insulating plaster supposed to achieve? You would already have to calculate with 5-10 cm of plaster to get even a somewhat reasonable solution.

You are not allowed to. The tenant can do whatever he wants. You have to ensure an unconditionally functioning apartment. Sorry.

I am on the path to realization. At this point, I don't like to say it, but unfortunately this time (as so often) is probably right. I spoke with the local Isotec company this afternoon. The expert was on the phone himself and took 20 minutes. Long story short: insulating plaster doesn’t make much sense. If anything, calcium silicate boards on the two exterior walls – also so that we landlords can have peace in the future.

Cost approx. €4,000 including VAT for about 22 sqm of wall area including relocation of electrical connections, Q2 filling, wallpapering, and final coating.

Exact offer will be available after the on-site appointment on 01/15.

I think we will have it done that way.

I just have to figure out how to save the expensive parquet since the heating also has to be moved inward a bit.

I see such obligations more often and they work if the resident isn’t particularly difficult.
With some structural peculiarities, last summer it was concrete canopies, it was even impossible to place larger furniture against the affected wall, and sometimes the renovating painter prescribes that you may not paint over his calcium silicate boards, etc.
Whether you are allowed to specify that? I wouldn’t be more papal than the pope there.

Well, in the end you have to rely on your knowledge of people anyhow and take the tenant who makes the most reasonable impression...

P.S. If it is mold caused by structural reasons on the exterior wall, you should hold the owners’ association accountable. The exterior wall is joint property. We also had to do two apartments last year. They got two walls completely covered with calcium sulfate insulation boards.

That’s true, and I have already thought about it. But who likes to make enemies with their co-owners? And for around €3,000 before tax considerations.

It would be interesting to know if other apartments in the building have similar problems. Have you talked to the neighbors above and below you?

We are the only ones with the problem. Below us is our basement compartment – no problem there. Above us is an engineering office. According to the owner, there is no problem there either. Above that, in the attic, is the kitchen of the apartment. Also no problem there apparently.

Our condominium is the only one whose original floor plan was significantly changed. I already dealt with the chain of resulting mold-promoting causes in a previous post.

Thank you very much for the lively discussion. I am on the path to insight. At this point, I don't like to say it, but unfortunately this time (as so often) is probably right. I spoke with the local Isotec company this afternoon. The expert himself was on the phone and took 20 minutes. Long story short: insulating plaster doesn't make much sense. If anything, calcium silicate boards on the two exterior walls – also so that we landlords can have peace in the future. Cost around €4,000 including VAT for about 22 sqm of wall area including installation of electrical connections, Q2 filling, wallpapering, and final painting. A detailed offer will be provided after the on-site appointment on 15.01. I think we will have it done that way.

In the end, certainly the most sensible solution and also a sustainable solution in the long term. Especially mold issues like this should not be taken lightly. In these cases, I often read about complete solutions, that is, interior insulation, reinforcement, fillers, etc., all from one manufacturer with coordinated components. The whole thing processed and carried out by professionals. You won’t get anything out of it if you repair something somehow now and after 3-4 years you have the problem again.