Mold on the basement windows after screed

Hello,

following situation:

The screed was laid on Monday/Tuesday this week. The basement windows were probably closed. On Friday I was able to enter the building again and opened the roof windows for ventilation on the upper floor. On Saturday I also opened the basement windows and noticed that there is black and green mold everywhere on the plasterer's formwork.

Normal? Serious? Very serious?

What to do?

Best regards,

Melrin

Completely normal - is the worst time for screed, because you can basically only achieve a somewhat normal climate through technical drying.

Hope you only leave the windows open briefly?

Completely normal - this is the worst time for screed, as you can basically only achieve a somewhat normal climate through technical drying.

Hope you only leave the windows open briefly?

Thanks for the tip, no, I actually had them open the whole (and first) night. How is it best to ventilate the construction site?

Ventilate by shock airing for half an hour - several times a day. And since that usually doesn’t work, you have to dry technically.

For the screed, this kind of ventilation is not good - you should avoid it.

By the way, this gets even worse if you heat - or are you already doing that?

No, fortunately not yet.

So I will close the basement windows again at night.

Why can't I leave all the windows open during the day if it's not raining?

Because the screed then dries out superficially – cracks and excessive curling can then follow.

But the screed layer installer should normally have explained that to you...

And during the day would be bad anyway, because you bring in even more moisture ;). In the current season, only ventilate in the evenings/nights – or (I repeat myself) dry technically, which would be the only proper choice.

If you have nothing with accelerators, the screed must now cure for 21 days (at least with ZE) and be ventilated regularly.

Vapor barrier already installed? If not an inhabited attic, is there an accordingly sealed staircase already in place?