joining new plaster to old, advice please.

[happyhero]

My bedroom ceiling is plasterboard with what looks like multifinish on it and I have just done some work which has ended up with me cutting in a new piece of plasterboard about 500mm x 1000mm, how do i join the plaster?

Can I feather in some multifinish and if so do I need to prepare anything, i.e. pva or tape edges?

But how do I tape joins if existing side is already plastered?

Any help appreciated.

 

[PrenticeBoyofDerry]

Where the new board butts up to the existing plasterboard, you need to rack the plaster back to surface of existing plasterboard. Do this along the full length of joint, removing about a 50mm wide strip.
This will then allow you to tape across the joint of the two boards, then you can blend the finishing plaster across the joint.
I would PVA the area where the joint is, just as a precaution, so old plaster does not cause any unwanted suction.