What to use to stick small area of plasterboard to painted wall

[User1234567890]

I've boxed in some pipes and there's a small external corner that I have built out with a wooden frame, and then it meets the old existing corner. I will be fixing to the wooden frame, but about 20cm x 7ft of the new board will be over an old, 2 part plaster/ and mortar wall. I will prime the old wall with gardz, but wasn't sure of the best thing to stick it on with at that end. Grab adhesive, like pink grip or something else? I can't really do mechanical fixings, as there's a lot of wires and a gas pipe directly behind the old part of the wall. Added a pic so you can see. Cheers.

 

[Wayners]

I'd stick some plasterboard behind existing with clear Stixall.
Then stick some plasterboard over with Stixall.
That will give the new peace something to stick on and not flex along joint

Toupret powder filler to make good and fill hole

 

[robinbanks]

That was close!

For what it's worth I'd consider straight up installing an entirely new sheet of plasterboard; rip that old one off then you're not messing about trying to support a joint

 

[User1234567890]

Thanks mate, there's another long piece of timber, not in the photo that screws to the timber on the left in the photo and sits flush (ish) with the wall to accommodate the new board. Cheers for the info.

 

[User1234567890]

View attachment 391336

That was close!

For what it's worth I'd consider straight up installing an entirely new sheet of plasterboard; rip that old one off then you're not messing about trying to support a joint

It's about 15mm off There's no plasterboard here at all mate. The white painted bit is really old 2 part plaster and under that is a cement render of some kind, and is rock hard. 1950s build. The blocks underneath are pretty crumbly cinderblock, so bashing off back to the blocks is not easy in this part of the house. In others, the plaster falls off if you look at it

 

[robinbanks]

Ah, I see. I thought it was a sheet on the studs that didn't go all the way across. Might it then be easier to pack the studs out with a bit of batten so they finish flush with the surface of the white area, then foam up the white bit with low expanding foam/pb adhesive foam and stick a new bit of PB over the whole lot, screwing it on the stud side (32mm screws, won't hit any pipes etc)