Botched work in the bathroom? Drywall instead of plaster

What exactly does the contract say? Are there witnesses for the conversation about the surface-mounted fittings?

Only the two of us were present at the conversation, the company owner and me. The contract lists two items under "dry construction work" - the paneling of 1. the WC and 2. the risers. Nothing else is mentioned. Not even optionally.

Hard to assess. "Die Beplankung von WC und Steigleitungen" can presumably be interpreted in many different ways. This shows that one should not sign contracts without at least some execution plans – even if they are only hand sketches. I therefore see a certain degree of contributory negligence. The only solution is to sit down together and look for a solution.

Talk to the company. From my experience, it is not uncommon that only the bosses have a precise plan, but unfortunately do not always clearly communicate it to their employees, which then leads to different implementations. If even such important things as the installation dimensions for the washing machine no longer fit, then it is essential to react now before more damage occurs. Currently, it is still relatively easy to fix. We also currently have a major construction site (Kernsanierung EG) and I’m glad to be at home. There are frequent inquiries about details, even though the boss gives instructions in the morning. Often it only becomes clear little by little, especially in old buildings. And I know the problem that sometimes you have to fight for every centimeter because every centimeter simply counts.