The base plate was cast too large - it has now been shortened - is that okay?

For me, there is only one way:

1. Stop construction
2. Grab a spade and expose the foundation (a meter wide is enough)
3. Call in a structural engineer to inspect the slab and foundation

4.1 if the structural engineer gives an written OK, the matter is settled for me
4.2 if the structural engineer gives an written NOK, write a defect report and set appropriate remediation + deadline

Steps 1-3 preferably in the presence of the head of the construction company. If 4.2 applies, you will probably need an expert.

That’s how I would do it (and had to do it, as our foundations were not deep enough and consequently had to be buttressed all around based on the defect report)

Unfortunately, this is not an April Fool's joke.

So it is now "finished".

What does the structural engineer who planned and signed off on the strip foundations, etc., say about the subsequent shortening by 16 cm??

**edit: is the black stuff latex or bitumen?

Good question what the structural engineer says...

The black is [Haftgrund].