Fast screed, advantages - disadvantages, additional cost, experiences?

Hello forum community,

I have received an additional price offer for fast screed, the additional cost is 1500 euros for about 120 m², according to the offer it states:

The cement fast screed (VELOX 7 cement fast screed) therefore offers you the advantage over the usual screed system that it is walkable already 24 hours after installation and loadable from the 4th day after installation with 70% of the contractual load. By using fast-drying screed, you can thus save about 4 weeks drying time.

According to the calculation (4 weeks), I would have saved 1 month of rent and 1 month of loan interest, that would be about 1900 euros, would something like that be worth it? Especially since I don’t know if the following trades would then be suitably available and the lead would be lost.

According to Google:
An ordinary cement screed is walkable after 3 days and slightly loadable after about 1 week, but its readiness for covering or full load capacity is only reached after at least 4 weeks. The readiness for covering is reached when its residual moisture corresponds to the air humidity of the room air.

During the drying phase, I wanted to at least fill the walls to Q3 or Q4, meaning that I can enter there after one week or are there problems with the walkability?

P.S. The drywall construction in the house is already finished, I hope that this is not a disadvantage.

It’s not like I can just pull the amount out of my sleeve. I’m still not so sure. Who among you already has experience with this?

With us, 5 construction dryers remained inside for 4 more weeks until release and measurement were okay (normal screed). At a colleague's place, it was dry at the first measurement by the tiler, but when the carpenter relied on that a week later or so, the parquet later warped (probably due to new moisture in the meantime) and had to be removed again.

... to your question, I can't contribute much, just wanted to emphasize again that the values should be correct here :)

Normal screed actually needs a good three weeks before you can start the heating program (takes at least another three weeks). From when and how can you work with your screed? What protocol did you get from the screed layer for the underfloor heating? The surcharge, however, is more than hefty! I had a variant where I could glue the parquet after just over a week. So it saved me six weeks.

Whether the additional costs are worth it for you is something you have to decide. We had to use fast-drying screed for the first house because there were delays, but the subsequent trades were scheduled and the move-out from the rental apartment was also getting closer, so we had no other choice. Of course, the actual measured values ultimately determine the readiness for covering and not the general specification of the manufacturer, but in our case, it matched pretty accurately. We will now use fast-drying screed again because I finally want to finish and am fed up with the endless waiting ;) .

We had 5 drying units running for another 4 weeks until release and measurement were ok (normal screed)
With a colleague it was dry at the first measurement by the tiler, but when the carpenter relied on that a week later or so, the parquet later warped (probably due to new moisture in the meantime) and had to be removed again.
(...)

I would rather suspect that the tiler measured in the bathroom and there, for whatever reasons, the screed was already ready for covering.
In the bathroom, underfloor heating is usually denser because it is designed for a higher temperature.

The parquet layer then simply installed it in the living room, even though he should have measured there himself again... he certainly included the CM measurement in his offer.

I don't believe in this whole rush and would rather save the money.
Because you say it yourself:
In the end, the follow-up trades don't come immediately afterwards anyway, then the construction site stands for 4 weeks and you have both the extra cost AND the rent/construction time interest on your neck. You can also walk on normal cement screed after a few days. How else should you ventilate 3 times a day from the fourth or fifth day...
Only punctual loads should be avoided for some time, so you shouldn't climb a ladder carrying a 50kg sack on your shoulders.

If you want to do your own work anyway, then there is no reason to speed up the construction process with fast screed?
Putty and sand all walls to Q4, that will certainly cost you 2, 3 weeks. Can you do that?

The term "Schnellestrich" means nothing without additional information from the manufacturer. What does the "speed" consist of? Is it the early setting, allowing quick use for subsequent trades, or is it the rapid water binding, which leads to quick readiness for covering? There are screed binders that can do both. But they are naturally more expensive than a standard binder. While the manufacturer's specifications can certainly be relied upon for quick strength development, it looks a bit different for fast covering readiness. Because the drying conditions also depend on the environment, thus the climatic conditions on the construction site. For example, if relatively high humidity of 80% exists in the building due to newly applied wall plaster or similar, nothing can and will dry there. Therefore, according to the manufacturer's specifications, cross-ventilation must be carried out – and the room climatic conditions must also be monitored with a thermometer/hygrometer (and preferably documented). The screed layer has just as little influence on the drying behavior as the binder manufacturer!
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It is also true that cement-bound screeds can become moist again at high surrounding air humidity after the installation readiness has already been determined by CM testing. In a case I worked on, a luxuriously equipped, listed villa, the high-quality parquet had to be completely removed after the parquet layer installed the parquet only 7 months after his (otherwise excellent workmanship) installation. Much too late after the CM measurement. Therefore, the notes listed here on this topic must be observed, that a fast-drying screed cannot be used sensibly if the subsequent finishing trades cannot proceed in a timely manner.
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Construction – a complex, highly interesting field, and one fraught with many pitfalls for the technical layperson!
Regards: KlaRa