Water damaged ceiling repair

[spader]

We had a water leak from the loft while working on the water tank, and the ceiling came down.
The question I have is, what is the bit exposed after the plaster has came off?
Could they be plaster board? Or some other type of boards? They look like card board to me.

What has come off from the ceiling is the outer plaster (which I put on years ago), and also a layer underneath the plaster, which looks like either the old plaster, or plasterboard (about 1cm thickness). There is about 1cm gap between this layer, and the boards exposed.

Then going back to the first question, what are the boards showing are? Can it be attached with the new plasterboards, and will they hold them if they were attached using the plaster screws? Because they look soft and appear to some cardboard type. They are drying off now, and I am waiting the work until they are totally dry.

In the beginning, I thought I could just plaster over the exposed area, and level it up for painting. But more I look at it, it looks like it won't work.
I need to attach some sort of plasterboard securely, and then plaster over the newly attached plasterboard to make it level, it seems to be.

I am just not sure if the exposed board can securely hold the newly added plaster boards with screws.

 

[Wayners]

Dig a bit through paper layer with a screwdriver just expose the soft gypsum plaster behind the paper layer.
If you have no idea what plasterboard looks like call in DIY store and have a look.
Is the board level?
If so SBR and plaster skim over

 

[ree]

The edges of the patch show the finish is blown plaster.There are no signs that from new the skim ever took to the plasterboard. Cant see much p/b nailing either?
Whatever you do you will have to re-skim the damage. So why not knock off skim back to bonded finish, and cut out a square of p/b as far as convenient joists. Then screw a new square to the joists or ledgers pinned to the joists. Noggins will be needed as well.