How is this 50s wall built?

[JohanVSF]

Apartment from the early 50s. I'm curious about how it was built then. One of the nails pulled some material with it when I was removing a door casing, conveniently leaving a small crater that shows the entire wall in cross-section. So how did they build back then? What are the different layers? Can it be seen?

The outermost layer is a pink latex paint, I note, on top of an older mint green paint from back in the day.

Then there seems to be some kind of plaster on a core of some kind of concrete/cement? I'm just guessing.. I don't have a great understanding of this, but I would like to!

 

[Claes Sörmland]

Wall made of some sort of blue concrete/slaggsten/concrete stone that has been plastered in layers and painted.

 

[JohanVSF]

Murad vägg av någon sorts blåbetong/slaggsten/betongsten som putsats i lager och målats.

Ok! Thanks for the quick response!
I was thinking of putting a skim coat over the outermost latex paint. Could there be any issues with adhesion then?