Rust spots on concrete - ceiling to wall - new construction

Hello,
yesterday we had the acceptance appointment (new building). There are 40 terraced houses, but apparently only we have the problem.

There are various rust spots between ceilings and walls on the ground floor. In total, 6 spots that we saw.
2 rust spots are very large, about 3cm, another spot about 5mm, distributed on the ground floor. Attached is a photo of the largest rust spot. The spot is even still wet.

The site manager said that this comes from the connections between the concrete walls. He will fix these defects. In 3 weeks we have the handover appointment and these defects will be repaired by then.

We wrote this in the protocol and accepted the house.

But I couldn’t sleep at all last night, is what the site manager said correct? If the defect is not properly repaired, will the house no longer be stable after a few years? It does not seem simple to me to fix these defects.

What should we do now? Unfortunately, we have no expertise...

Thank you very much for the help.

That is only a cosmetic defect; if properly repaired, you don't need to worry about it.

Thank you for the reply. But where could the rust come from? And it is still wet... If it were only one spot, it wouldn't be a problem, but there are 6 rust spots in the 50sqm living room...

The rust comes from the reinforcement... as soon as the walls/ceilings are dry, the rust will stop... absolutely normal with concrete and not a defect per se, meaning just an aesthetic issue

Hello "Nemnem". The photo is (at least for me) sufficiently conclusive. If this were a cause due to built-in reinforcing steel in the concrete, the situation would look different. In masonry walls, we have no steel reinforcement, and why should we. If we open the spot we see in the photo right up to the cause, we will see that something (let's call it "Rödeldraht") was installed there that normally does not belong there. Reinforcing steel would only rust if the minimum concrete cover was not maintained. However, in that case, in the following years there would be an "unhappy end" with rust flakes falling off. I do not see this in your case, though. Therefore, I partially agree with my predecessor who calls it a "visual issue." Which, however, must be rectified (not can). ----------------------- Regards: KlaRa

I would fully agree with KlaRa. But what if it is actually reinforcement that is not sufficiently covered at these points? Can that be ruled out?