Concrete wall broken. Repair.. how?

[mcax]

Hi, bought an old apartment from 1960, not renovated since then either. Removed the wallpaper and the wall fell with it. It's just in one spot but I still wonder how to fix it in the best way. It's about a cm deep and 20cm wide. When I knock, I hear that it's loose a bit more around it. Should I remove that too?
Thanks in advance.

 

[Stefan N]

If it is loose, remove it, then it is easiest to repair with gipsputs.

 

[mcax]

If it's loose, remove it, then it's easiest to fix with gypsum plaster.

Thanks for the help, it was super easy and looks good. We'll see how it looks once it's dried.

 

[anders07]

That looks like blåbetong so consider covering it with something dense, e.g. Microlit and paint with dense paint.

 

[mcax]

That looks like blåbetong so remember to cover it with something dense, e.g., Microlit and paint with dense paint.

Okay, directly on the concrete or?
I have already applied gypsum plaster.

 

[anders07]

Yes, then outside the concrete to enclose any Radon gas... (if it's blue concrete, but I'm quite sure it is).

It doesn't have to be a problem at all, but since you're already at it, it's just as well to fix it properly, I thought...