Lime plaster ceiling repair (not not in this case)

[photogav]

I hope this is the right forum to place this one. I have an old cottage with lime plaster just about everywhere. When I was renovating it I replaced some of the stud walls with plasterboard instead of lime on laths. However, in my office I liked the wonky floors, unstraight walls and ceiling.

However on one side there are a few spots where the line render has nail popped in a fairly big way. Over the years I have tried various ways of repairing it from scrim taping the nail heads (they will not come out) and filling the hole with lime plaster to trying to build up small layers of various types of filler. Nothing works. The lime shrinks and pops, and the newer fillers fall out too after a month or so.

I have included a couple of pictures to show what I mean.

Does anyone have any idea what I could try?

 

[bobasd]

i gues the damage is on the ceilingand the nailheads are pinning up plaster laths?
your photos show the damage at roughly equal centres.maybe plaster laths have been fixed to centred joists? if you gouge out a little more of photo 3 it will be obvios what is being nailed to.
nailed fixings can be tapped back from the surface or removed with pincers.
after drilling pilot holes,laths over joists should be screwed back up.
push up the ceiling around the above area to see if its also saggin from its fixings?

after cleaning off any loose stuff,wipe on a little white glue/pva andfill an repair using a small bag or bucket of easi-fix or similar plaster repair.

whats happening above,is it the loft or an occupied room?