Install click vinyl despite possibly too high residual moisture.

Just beforehand:
Yes, I wouldn’t recommend this to anyone myself and yes, I know that a CM measurement must be carried out, as that is the only really valid method to measure the residual moisture.
And yes, I know we like to lecture here in the forum, but I ask you to put that aside briefly and follow me.

Our CA flowing screed (alpha-hemihydrate) was laid on 26.07.23. Afterwards, the windows were closed for three days and the house was not entered. Then we started ventilating several times a day with shock ventilation. Always keeping an eye on the hx diagram to achieve the lowest possible relative humidity in the house according to the outside conditions.
After three weeks, the functional/cover readiness heating began. The flow temperature was gradually increased and after 5 days was maintained at 50° for a further 14 days. Afterwards, the temperature was slowly reduced to 21°.
Then I determined a residual moisture of <0.2% with an electrical measuring device (yes, inaccurate). So at least the indications look good so far.
Then we had no heating for about 4 weeks, but still ventilated (again optimally according to the hx diagram). Since last week, we have heating again, running at 21°.
So much for the information.

The following problem:
We have to move in before Christmas because we have already terminated our rental apartment and the repayment begins. That means we could only afford that to a limited extent anyway. It would be basically impossible.
From the end of next week, we will lay click vinyl floating. Wineo 600 rigid. Now let’s assume I wouldn’t do a CM measurement. What is the worst that can happen to us, or does anyone here have experience with this? We would leave off the baseboards beforehand and only mount them after a few weeks. We would also only cover the necessary rooms such as the bedroom & living kitchen.
And again, I wouldn’t advise this to anyone myself, but unfortunately we really don’t have a real choice anymore…

to call. Hopefully, they can provide professional advice.

Just do the slide test: https://www.hausbau-forum.de/threads/lage-stadtvilla-oder-einfamilienhaus-auf-500-m2-grundstueck-rechteck.33505/post-538361 The second paragraph in the lower third describes how it works.

The manufacturer, which is Windmöller GmbH, specifies the following in their installation instructions for "Wineo 600 rigid":
"Deviating from DIN 18560, we recommend a maximum residual moisture of ≤ 0.3 %CM for CA heated screed".
DIN 18560 Part 2 specifies a maximum residual moisture of ≤ 0.5 CM-% for CAF.
This means that the carrier board of the design floor covering reacts to (rising from the back) moisture.
Anyone who does not carry out a CM measurement cannot state whether the subfloor is ready for installation accordingly.
This in turn means that whoever installs it anyway bears the full residual risk.
But the original question was what could happen under the circumstances that the subfloor is still too moist.
Well, this condition would lead to swelling of the carrier board, accompanied by warping and length changes.
How extensive these undesirable features are cannot be stated.
In the extreme case, the new top covering is so warped that trip hazards form, the locking heads release from the locking mechanism, and it rises several millimeters.
An irreversible total loss so to speak, which requires a complete renovation, possibly also involving the removal of the kitchen furniture.
The "foil test" mentioned by another forum participant allows for a fairly good, that is, meaningful forecast.
For this you need:
- two hygrometers
- one thermometer
- a thicker PE foil, approx. 40cm x 40cm
- adhesive tape
- pen and a sheet of paper

The underfloor heating must be running, the room well ventilated, and then the foil placed on the screed.
We place the first hygrometer centrally under the foil, then the edges of the foil are tightly sealed on the screed surface with adhesive tape.
After approximately 24 hours, hygrometer 2 and the thermometer are used to record the indoor climatic conditions that have established themselves in the room. Only then are hygrometer no. 2 and the thermometer placed on the outside window sill, the window closed, and after about 30 minutes the two exterior values are recorded.
Now we read the relative humidity under the foil. The temperature is the same as that first measured in the room.

Evaluation option (1):
If the humidity under the foil is <65% and identical to or lower than that measured in the room, then one can assume sufficient drying of the screed.

Evaluation option (2):
This is somewhat more complex but more precise; however, a building physics data table is required to weigh the absolute moisture content (in g/m³) outside as well as under the foil against each other.

Option (1) should suffice for the layperson.
However, as stated at the beginning, the CM residual moisture measurement (note unfortunately) is the only recognized method.
The foil test is based on the KLR method and is hotly and controversially discussed in the professional field.
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Good luck with the further procedure:
KlaRa

Why don’t you just have a measurement taken? Then you are on the safe side and also have certainty for yourself.

Why don't you just have a measurement done? Then you are on the safe side and have certainty for yourself.

Maybe we should ask the questioner first whether there are any measurement points marked in the screed at all? Not an insignificant aspect in order not to hit the heating pipes with hammer and chisel during sampling ...