Mold in new construction on drywall

Hello everyone,

we are currently building a single-family house and unfortunately have a mold problem. In several rooms on the upper floor, there are clear mold formations on the gypsum boards (Gipskartonplatten), which appear as small black spots. The mold covers an area of about 2-4 sqm per room. The density of the spots varies depending on the room.

The cause is likely the high humidity in the house due to plaster and screed, which, despite ventilation (3 times daily, each time 20 minutes of shock ventilation and wiping down all windows and doors) and the heating system's screed drying program, still remains at about 80-85% in the mornings 5 weeks after the screed was installed.

Our building expert (not a mold specialist!) is of the opinion that all boards should be replaced. Afterwards, dehumidifiers and fans are to be set up. The builder seems to agree with this. More details will be clarified tomorrow.

I now have two questions:

1. Are the aforementioned measures sufficient, or should a mold specialist also be consulted to identify the mold fungus and conduct an indoor air test regarding spore concentration, in order to possibly derive further measures? I do not want to go overboard, but also not take the mold lightly.

2. We had already filled and sanded the gypsum boards ourselves as a DIY job. Does the builder have to restore the replaced boards to the same condition at his own expense, meaning filling and sanding?

3. Can someone recommend a mold specialist in the Stade/Altes Land region or possibly Hamburg?

Best regards
Supergrover

The cause is likely the high moisture in the house from plaster and screed, which despite airing out (3 times daily, each time 20 minutes of shock ventilation and wiping down all windows and doors) and the screed drying program on the heating system, still remains around 80-85% in the morning, 5 weeks after screed installation.

Precisely because of the screed drying program, moisture is being expelled from the screed.
Drywall panels should only be installed after the drying is completed.
Dispose of all drywall panels with mold and, depending on the size of the house, run about two dehumidifiers for a couple of weeks until hardly any water accumulates.
If the substructure is made of wood and the battens are not yet affected by mold, consider treating the battens prophylactically with anti-mold spray.

Whether the builder will at least partially cover the costs for filling and sanding depends on your persuasion skills. I think he will deny it; getting money back is difficult.
You might be able to negotiate with him for "compensation" in the form of an additional construction service at his expense (maybe digging a hole somewhere or something like that).