By chance, the expert was on site... and he and the concrete supplier even spoke to the 3 people, telling them that it would leak again... apparently they did not understand.
We had a construction expert on site, thank God, because he just happened to be there when the mess occurred.
That someone is grateful that such nonsense can even happen in the presence of an expert, we have not seen here either. If you didn’t commission and authorize the expert to stop wrong things if necessary before they become final, then at least the following further procedure would have been appropriate: namely that he immediately prepares a qualified notification of defects for you, with which you then run to the lawyer [U].
Your story reminds me of a joke about the local Kölsch humor figures Tünnes and Schäl: Tünnes put a pot of milk on the stove and had to leave briefly. He told Schäl to watch carefully when the milk boils (he of course meant to turn off the stove then). When he returned, the milk had boiled over and Schäl proudly reported that he had watched closely as instructed; it happened exactly at ten o’clock.
The actual foreman was on vacation [...] The joints were also sealed with expanding foam [...] When it started leaking, they panicked and quickly stuffed battens underneath.
There is absolutely nothing sealed.
Doesn’t matter, the workers are obviously not exactly sound either, so it fits (at least together). A foreman who goes on vacation with no replacement and a team that mistakes battens for pressure-proof sealing lips: that sounds to me not like a "renowned," but rather a "notorious" cellar builder.
I have to give the cellar builder credit that he did not try to downplay the crap, but immediately offered the black tank.
I am just imagining having forgotten the bulletproof version on the Chancellor’s A8 and now generously offering him
instead a metallic paint job at no extra cost. Please tell me you don’t seriously believe that you might now get something possibly even more valuable???
Your cellar is junk. Have it removed and replaced by a properly built one. Hopefully the "renowned" cellar builder has enough money to cover all consequential delays!!!
If a cellar has to be executed as a "white tank," there are reasons for this, and a coating is nowhere near sufficient to substitute it. What kind of idiot must the expert be if he does not at least unambiguously say this to you unsolicited? - I can’t believe it!
I see "reproducible" problems in this constellation, which could continue with another cellar builder (and would check whether I wasn’t parting ways with the wrong troublemaker here). [...]
P.S.: I say this repeatedly for good reasons, that you should never order a cellar yourself, but rather include this delivery and service package in the scope of the house provider’s contract. OKKD is a critical interface!