Screw directly into aerated concrete

[cryssarn]

It really sounds a lot like the first layer is plaster and not any lightweight concrete. What's behind it is harder to determine.

I would investigate the wall construction a bit more before making any definitive decisions. Maybe consult with the board? Maybe post pictures here?

I can post some pictures of the holes that were already here. However, I guess they have been worked on for a while and hollowed out a bit, as they didn't become quite so hollowed out for me. It's a rental via Victoria Hem, so no clue there so far.

 

[Pyka]

Check with the janitor, he has probably screwed something into those walls.