Hope you can help.
I've got a bare plasterboard ceiling - about 2m x 2m - that I need to plaster. Unfortunately, the underlying joists were anything but straight and level, so the plasterboard is fairly curvy. The random nature of the wobbles meant that it wasn't really practical to try straightening it up with wood spacers before putting it up (and I didn't want to lose room height by putting in a false ceiling)...
In order to get a level ceiling I've fixed up wooden grounds over the plasterboard and would like to pad out with undercoat plaster before a top skim. In most areas this will be to about 8mm (+2mm topcoat), but in one corner it goes quite deep, so that by the time you're right in the corner the overall plaster depth will be 25mm deep (undercoat + topcoat). Is this ok weight wise? Reading some of the tiling forums, I believe plasterboard walls are rated to about 32kg/m^2, so working it out I should be ok...?
Some specs: 12.5mm plasterboard, 3"x2" joists at 16" centres, plasterboard screwed to joists with 45mm screws, at 6" spacing along the joists.
So, is this likely to be too deep/heavy, or ok?