Hello! We're redecorating our entrance hall and while removing the wallpaper off one of the walls we noticed that it was some sort of cardboard instead of plaster. The idea is to paint this wall but I'm not sure how I'm going to do that now. Should I plaster it first (not sure if it's possible because of said cardboard)? Or should I remove the whole thing and then plaster it? I'm not sure what's actually underneath. Any help is appreciated!
https://imgur.com/a/JPU31ke
https://imgur.com/a/JPU31ke