How do I fix this wall?

[ssmart]

I'm brand new to this, and worried I might have made a big mistake already.

A portion of the wall had (ugly) textured wallpaper on it. It was coming up at the edges and I found that most of it tore off pretty easily. I planned to replace it with plain lining paper and a coat of paint.

The problem: I began reading about plasterboard and realized I have no idea what I'm dealing with. Is it plasterboard underneath or has it been skimmed? I can't even figure out how to tell. Most importantly, if it's plasterboard, have I damaged the paper layer of it? And if I haven't, can I paint directly onto the walls (I haven't finished removing all the wallpaper yet, but after that)?

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[1john]

Are you left with a chalky substance that you can pick through with your finger nail, if so it's the plasterboard core, if its pink and quite tough then its been skimmed.

 

[vv2806]

Most importantly, if it's plasterboard, have I damaged the paper layer of it?

The paper layer of the plasterboard is on its back, so it is very unlikely you have damaged it

 

[joe-90]

Coat with Zinsser Gardz and see how it comes up.