TMC coughed up some electrons that declared:


It does seem very odd
I cannot work out how they could put up the plaster board before the
joints or why on earth they would want to do so

My thoughts exactly. It would have been a bodge if they'd used small offcuts
of PB. This is just perverted, but not in the Jemma Jameson and a vat of
whipped cream sort of way...

As to a solution I think that I would use some 12 mm ply and put
individual pads under each joist

Sir, you are a genius. I reckon I could cut and chisel out the PB under each
rafter one by one from above and tap a bit of ply in. I could arrange to
lift each joist a fraction using the neighbours just to make it a bit
easier. Seems that if they've used 12mm PB as packing, 12mm ply should get
it back in the same place. I'll check the thickness of the PB in question.
Might just do this without damaging the ceiling.

Time to buy that Fein...

this would be the easiest thing to do and would be better than the
original

I would not even bother fixing the pads in place the weight of the joists
will hold them

Thanks for giving me confidence. If it turns out the wall top is too rough I
could always put a bit of Plastic Padding or similar epoxy in too.

Cheers and many thanks indeed.

Tim