repairing (?) plasterboard ceiling ....

Well, depending on how big I suppose. The smallest deformation can often be pushed back with some new dampness, but prolonged upward force is needed from a post. Brian

Remove damaged plasterboard, insert some wooden battens to bridge the hole, screw battens to existing PBoard, cut a piece of PBoard to fit the hole, screw the new Pboard to the battens, fill the edges, re-stick paper, have a glass of wine.

Ah, starting to sound like a plan ...

Cut out damaged section and cut a repair piece of plaster board that over-laps a couple of inches all round. Put in place from above with a brick on top seating on sloppy wet plaster. Cut second repair piece that fits the hole but is smaller by 3/8" all round, butter with a bit of sloppy wet plaster and secure in place with plasterboard screws. When that has set plaster up the 3/8" gap using skrim in your skim coat. When set you can remove the brick for next time :)

Andrew

NT

cut out a large section - all the damage

cut a new piece of plasterbaord to fit the hole

get some 1 x 1/2 battern and screw it around the edge of the hole to thecexisting plasterboard, but jutting out to form a rebate

screw the new plasterboard to that.

Skim the resultant hollow with bonding plaster

sand it back if you are a crap skimmer

redecorate the whole section

or

Not sure I would skim it with bonding though... multi-finish or one coat would get a much smoother result.

That'd be me :)

was hoping to keep that bit to the minimum ....

As others have said cut out the damaged section and replace with a bit of new plaster board and skim. More detail and what I'd do:

Cut out the damaged bit plus a couple of inches. Then expand that area to half way across the nearest ceiling joists. Square (rectangle) the hole and fit noggings made from 2 x 2 between the joists hard down on the back of the existing plaster board and sticking out over the over the edge to form a rebate. Remove any skim arround edge of opening for about 2", deeply score it to stop too much coming off... Fix edge of plasterboard to noggins and joists with plasterboard screws. Cut a new bit of plaster board to fit the opening with a good 1/8" gap all round. Fix to joists and noggins with PB screws. Apply skrim tape along the the joins and skim, forcing the skim through the tape and well into the gap behind.

One thing that once worked for me. Cut out the bulging piece. Make it very wet, and put weight on it to flatten it (I generally have breeze blocks lying around in the garden). When dry, screw it to battens. If I'd had some No More Nails at the time, I'd have probably tried that, but I have a big bag of ceiling screws that I need to use up. I don't know if this is all officially a good idea, but the piece is still there, and can't be seen unless you really look hard for it.