Mold or not?

[ricebridge]

That's true. But neither their inspector nor we know exactly how far the mold has spread until it's opened up. That's why I'm asking.

 

[ricebridge]

The wood with gray on it at first glance looks like formwork that has been reused, meaning it's concrete residues. But you should be able to determine that by scratching it and seeing if it's hard.

Yep, further investigations show beyond all reasonable doubt that it's concrete residues. Thanks @Bernieberg, you just saved me a number of sleepless nights.

 

[Peter_Henry]

Yep, further investigations show beyond all reasonable doubt that it is concrete debris. Thanks @Bernieberg, you just saved me several sleepless nights.

Nice