Screed drying - Incorrect drying program set

What kind of screed is this? What you should avoid is the screed getting drafts. If you fully open the windows twice a day, it creates one hour of drafts in the house daily. I tried ventilating with tilted windows.

I am not an expert and cannot say whether something is wrong with your screed. However, in our case, the windows were still wet at the bottom edge in the mornings even after 4 to 5 weeks. At the beginning, we also ventilated too little for a very long time.

Before the screed is ground based on assumptions, there is the possibility to break open the screed at one spot to see the lower layer. This must be done at the points where the "Pinöppel" is stuck in the screed.

:
Please do not take away the only (official) way for the following floor layer to carry out a CM residual moisture measurement!! So leave everything as it is, without opening the screed construction. Moisture cannot be seen, only measured.
For this reason, it is unclear why the only correctly marked measuring point in the room should be opened "without necessity"—and above all without any likelihood of obtaining usable information.
Regarding moisture in the room:
Nowhere is it described that condensation must occur on windows during the installation of screed. So why assume a special situation, which can actually occur in new buildings can, as a prerequisite???
About sanding:
It is indeed the case that calcium sulfate flowing screeds are sanded to open the surface by releasing the pores so that water transport from the screed structure to the room air can take place.
But!
This requires the necessity to carry out such a measure. Such necessity arises only and exclusively if, after several weeks of ventilation, a residual moisture measurement (!) shows that the screed still has too high residual moisture.
When I read your contribution, nothing of the sort has happened so far, everything is based on assumptions and misinformation, thus on "fear-mongering."
It is best to leave the field to the experts.
The floor layer will carry out a CM test at the designated measuring point, record everything in his protocol, and hand it over to you (as the client).
After that, it can be decided whether any additional measures are necessary before laying the floor covering.
If you open the screed construction at the measuring point out of mere curiosity, the floor layer will no longer be able to perform a measurement, will raise his concerns, and put you in the position to decide how to proceed. You will then take on the responsibility and transfer of risks, even as a layperson.
Because the measuring point, where he can safely open the heated screed (and this is presumably what it is when measurement probes are indicated), will no longer be available.
So (deliberately colloquial):
Hands off the screed and wait until the professional (here: the floor layer) comes!
Wishing you continued success:
KlaRa

Hello KlaRa,

thank you for your detailed explanation. There are always 100 different opinions on such matters. As a layperson, this is naturally a high factor of uncertainty for me. At the neighbor’s, the calcium sulfate screed was measured after 7 weeks and was still too damp. The good man who carried out the measurement believed that grinding should have taken place immediately after one week. Likewise, the tiler, who by the way will also lay the tiles for me, said the same. I then called the screed layer. Dorte said that the grinding was only a cleaning grind and had nothing to do with drying. And this grind would also have to be carried out by the subsequent trade. This means I will wait a few more weeks, have it measured, and if it is still too damp, then I will grind and wait a few more weeks again? Most people then ask themselves why not grind directly. That can indeed drive one crazy.

Hello Stefan.
That is (almost) all correct that you noted there.
Ideally, after one week grinding should be done to give the screed time to dry faster afterwards. But technically speaking, that would be a service (the grinding), whose justification could only arise after determining the lack of drying. And after 1 week no screed can be dry (unless made with rapid cement or screed additives).
The mandatory cleanliness grinding of the floor fitter must not be confused with the initial grinding for better drying!
Unfortunately, as the client, you have to allow time and let yourself be driven by the circumstances!
The problem of non-drying calcium sulfate flowing screeds is well known to me from my own experience. For example, a heated screed still had significantly too high values after 6 weeks of continuous heating and ventilation. This is due to the pore size and the associated moisture transport mechanism.
This makes the whole matter even more complex than you might suspect.
Because in such a case, my professional group is responsible for the (also important for courts) assessment of whether this constitutes a "defect" (a legal term) or not.
My recommendation to you:
Nothing has happened yet. There is still no indication that the screed is unusually damp. As the saying goes, don’t spook the horses unnecessarily and look forward to what the floor fitter will tell you next regarding his result (of the CM measurement).
Regards: KlaRa

I haven't been able to detect any moisture development anywhere (on windows or on the concrete ceiling)? Really nothing.

Set up a hygrometer?

Apart from that, condensation requires high humidity and a temperature gradient. Here, it has been at least 15 degrees at night for weeks, usually 25 to now 35 degrees during the day.

I just wanted to find out if there’s anything I can optimize here. Nothing significant has actually happened that would require much thought. The heating program will start next week. I will set up the hygrometer. Of course, I don’t want to waste a lot of time if the screed is still not dry. Hence the question about sanding.