Fixing horse hair plaster

I have a few ceilings that have dropped away from the ceiling joists a little
They are all really decorative so cant be replaced without huge cost (I have done one that was beyond rescue but kept the centre rose)

I have had the insulation removed (all 1.5 foot deep of it!!) so we can see where it has dropped. I was going to glue above from the roof space and push up the ceiling from below and screw and support until the glue dries.

Does anyone have some advice?

Rod you are the expert, what do you suggest?

I have not bothered trying to repair the walls, I just replastered as most of them were beyond help and had detached from the studs a long time ago and cracked during the restump.


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