Is it sensible for the expert to inspect the base plate?

Since the site manager inspects your on-site work before erecting the house, it’s quite possible that he complains about defects if there are any. It doesn’t bother him at all, quite the opposite; if he sets his house on a faulty foundation slab and problems arise, he’s the one who ends up responsible... because he is the expert, he should have noticed it... If I remember correctly, there are also certain safety factors in building construction. No structural engineer calculates and designs a foundation so that it just barely works as long as the shell builder adheres perfectly to everything. They’re not completely stupid either. Also with the foundation earth electrode. That’s not so critical in the TN-C-S system, but it would be problematic in the TT system.

I just want to know if frost damage could have occurred due to the possibly premature removal of the foil

(...) I am grateful for any advice, but tips like "it would have been better to ... beforehand" unfortunately don't help me at all. As I said, the civil engineering company regularly works in snow and cold temperatures, and we have only heard positive things from friends and acquaintances where the foundation slab was poured under similar conditions. So I am not questioning whether the civil engineering company did everything correctly. I am only concerned whether frost damage could have occurred due to the possibly premature removal of the foil and whether an expert could identify this retrospectively.

Well, if anyone can do it, then an expert can. If you're unsure, get one involved.

It's clear that tips like these don't help you. However, this is a forum, and a lot of people are reading along who might be able to avoid this mistake because of these tips. Regarding your acquaintances... did they have an expert who inspected the foundation beforehand and the slab afterwards? If not, how do they know the work was done well?

I would always be very cautious with such recommendations. Just because the house is still standing where it was built after 5 years does not mean that all work was done 100% correctly.

You’re absolutely right, of course, but in this thread I was specifically concerned about possible frost damage caused by the removed foil. That’s not something a surveyor could have prevented in advance.

With our old landlord, the floor slab was poured in winter 2015, and since we are good friends with his daughter who lives in the house, we at least know that there were never any problems there. And their house construction company apparently said that they rarely see such a nicely poured floor slab. Our prefabricated house supplier also said that although the civil engineering company has been around for over 30 years, they have never heard or seen anything bad from them. So I really have complete confidence that they did it properly.

But to clarify once again, obviously someone partially removed the covering of our floor slab, because when we went back a week later, it was missing in some places. Of course, we don’t know when that happened. We only know that the day after everything was fine. Whether someone took off the covering on day 2 or day 6, unfortunately, we don’t know, because we weren’t on site in between (this is a new development area and there are always many onlookers roaming around).

The question for us is how possible frost damage can be recognized afterward if the foil was already torn off on day 2 (when it was -10 degrees at night). So, apart from cracks, is there anything else to watch for? And would a surveyor perhaps see more than a site manager?