Mold after 2 weeks

Hello community,
yesterday I discovered mold behind a picture in our new semi-detached house (external wall, insulated with some kind of wool – I don’t have the exact term right now).
The picture in the children’s room has been hanging for about 14 days and I am correspondingly shocked and confused.
We moved in 3 weeks ago.
Construction phase about 1 year.
Residual moisture in a new building is clear. Maybe I shouldn’t have hung the picture (it’s the only one in the house), but the mold formation seems very fast to me.. (diameter of the spot about 10 cm)
All our furniture etc. is a few centimeters away from the walls because of circulation/residual moisture.
We do shock ventilation in the morning, evening, and sometimes in between.
According to the baby monitor in the children’s room humidity is between 65 – 80%
Our underfloor heating is currently not on.
Now I’m very worried about this and also about the built-in kitchen, which is also, among other things, on the external wall.
How could I best proceed?
Should I immediately get an expert to inspect everything?
Is it enough to treat the affected area with ethanol or should it be sanded off or should a mold specialist be involved etc.?
Suitable preventive measures? Many always say “heat, ventilate, heat, ventilate etc.” – but how do you do that with a slow underfloor heating system?
Maybe someone has answers that can help me.
Thank you very much in advance!
C.

That sounds like you moved in too early. Did you measure the moisture before laying the floors? 80% humidity is already extremely high, I think.

I know from new buildings that after the screed is laid, the house is either heated for 4-6 weeks with dehumidifiers or with the heating on a special screed program. During this time, you have to regularly go to the house and ventilate, wiping the windows dry. The temperature in the house is almost 40 degrees. At least that's how I know it. After that, the residual moisture is measured and a decision is made whether you can move in, or wallpaper and tile.

I am not a professional, but I would remove the wallpaper at the mentioned spot and see if the damage is greater. When in doubt, always hire a professional, especially in the children's room. Maybe have your building inspected by an expert to see if there was any shoddy work. It might cost a few euros but in the end, it can be worth gold.

Or wait until someone with more experience responds. I’m just writing what I would do...

Hello,

obviously this is a massive wall construction?

Your descriptions sound like insufficient building drying.
By the way, I also wonder whether, for example, the maximum residual moisture of the floor was considered when laying the floor coverings (tiles, laminate?).

I once heard that mold can form at 70% relative humidity.
About 40 - 60% is, I think, considered normal.

I would simply confront the builder with this first and ventilate, ventilate, ventilate—as long as it is not more humid outside than inside (but I think this is not so problematic as long as it is not a basement).

Regards...

Hello,

Hello community,
yesterday I discovered mold behind a picture in our new semi-detached house (external wall, insulated with some kind of wool – I don’t have the exact term at the moment). The picture in the children's room has been hanging for about 14 days and I am correspondingly shocked and also confused. We moved in 3 weeks ago.
Construction phase about 1 year.

Has the drying program after screed been completed? When – after pouring the screed – were the walls wallpapered and did you already have problems during that time?

We do shock ventilation in the morning, evening, and sometimes in between.
According to the baby monitor in the children’s room, humidity is between 65 – 80%.
Our underfloor heating is currently off.
Now I’m very worried about this and also in the area of the built-in kitchen, which is also, among other things, on the external wall.
How could I proceed best?

I assume you did not have a ventilation system installed? Ventilating twice a day is definitely not enough! 80% relative humidity is definitely too much!

Before I give any advice here, I ask you first to respond to my answer; then we will see further.

Best regards

Hello,

during the construction phase we had mold growth. I had also reported about this here in the forum. At that time, I had the construction stopped and brought in an expert to determine whether it was a defect in the construction or just normal construction moisture. Fortunately, it was the latter. Since it was winter for us, it was relatively easy to remove the moisture from the house by repeatedly airing it out during the day.
The opinions of the expert and our construction manager differed greatly back then. The construction manager wanted to continue using drying devices and fans, the expert said, get rid of those things and air out several times a day. This works a hundred times better in cold, dry outdoor temperatures than one or several construction dryers, and he was proven right.
It was important that the house was heated properly before airing out because warm indoor air holds a lot of moisture. Then the windows were thrown open and you could literally watch the hygrometers drop from 75% to below 50%. This way, we already managed during the construction and finishing phase to keep the humidity permanently at a tolerable level between 50 and 65%.
Of course, this approach makes less sense in summer, especially since there is often high humidity outside due to the weather. But maybe you can at least use the somewhat cooler evening hours, provided it is dry outside, to air out once in a while.

This approach, of course, makes no sense,

Thank you very much for the feedback. I have already informed the BL and the moisture will be measured soon. The screed was laid for about 8 weeks before we started painting/wallpapering. The drying program was also running. About 2 weeks before the painting work, I still had a dehumidifier in the children's room, among others. About 5L of water came out daily. In the end, only about 2L. No problems with mold during the construction phase. Another consideration of mine would be the picture itself (it comes from someone who already had mold in their basement... the picture frame could have been stored there). Could it be that spores from the picture are transferring to the wall?? I checked the entire house after that... nowhere wet walls or mold. Should I maybe turn on the underfloor heating during the day and then do a shock ventilation in the evening??? Thanks again for your help!!!