After screed, mold or mildew stains?

Morning,

thanks for the input! Exactly, it is the ceiling and the walls. Pitch black and really formed within one night. Now after two days with one air exchange (as recommended - since this is probably enough for a small house) it is almost gone (see photo). I am still worried that it is mold and will come back. Therefore, I am leaning towards an expert who will either reassure me or advise me to replace the materials; in both cases, the 500 euros are worth it to me.

Best regards

What size house are we actually talking about? In the photo, I only see plaster and a concrete ceiling, right? There's not much to replace there. Mold only grows on organic materials. It might be that you had some small residues there. Then the problem can actually be gone as quickly as it came.

When the corners are completely dry (in my opinion, you can see that they are still damp), you can - if you want to be absolutely sure - treat them with a mold remover before painting. I don't think an expert will be necessary. However, continuing to ventilate a lot should be at the very top of the to-do list!

The ventilation intensity hardly has anything to do with the house size. The amount of moisture per room volume is the problem. Once a day is absolutely not enough. Feel free to also remove the condensation from windowpanes, window vacuum cleaners are practical for that.

The ventilation intensity has hardly anything to do with the size of the house.

Correct, there is no correlation with window ventilation. It would still be interesting to know how the house builder comes up with the idea to say, "The house is small. Ventilating once a day is enough!". Special case tiny house built solidly? :D

Thank you for the messages! Since the drying phase began, we have always had dry windows (no condensation, fogging, etc.) and our construction manager has explicitly said after several inquiries that airing out once a day is sufficient. The house has an area of 90sqm.