On Sat, 16 May 2020 20:48:24 +0100, John Rumm wrote:

I have a loose patch approx 2ft diameter on an overpapered lath &
hair plaster ceiling.

I can get to the rear of the laths (loft).

I would use a prop and a suitable size board to push it up from the
underside first.

I'd not push it right back up yet, just support it. Then go into the
loft and clean any grot away and any loose knibs. Then:

From above, then give the whole area a liberal coat of neat SBR (or
slightly diluted PVA if you can't get SBR), ...

So that it pentrates into the gap between plaster and laths and
broken knib joints. Then depending on how much chance there is of
getting plaster into the ceiling/lath gap, add the fairly soft
plaster, working it into the gap. Then jack the ceiling up. Hopefully
to make new knibs or at least fully filling (where you can) the
ceiling/lath gap.

--
Cheers
Dave.