Im helping a friend build there home- last month we hung the celing drywall and had a friend finish the seams (hes retired from this feld of work !) the problem is now the seams in the celing are cracking and forming a downword protrusion like the drywall is pushing out the mud and paper tape - NOT the end seams just the edge joints!!nowere else is cracking. the drywall is glued & scrwed to dry joists the roof was on before any rain hit!! what would cause this. the finisher said hes never ever seen this in 50 some years in the buiness. ANY IDEAS ???
Re: drywall cracking
It's good that the roof was finished before hanging the ceilings, but was the framing really dry before hanging the sheetrock? If the boards were peoperly hung perpendicular to the joists or trusses and the framing shrank, it would still push the boards together thus causing the edges to bulge. The end joints, moving equally together, wouldn't show a problem as quickly though they may still give trouble later. If you know the exact span of the house and/or room(s) when built, you can check it again to confirm if there is appreciable shrinkage. The only other possibility I can think of is a severe humidity buildup in the attic. Investigate the attic veltilation while you're up there measuring. And if you've already insulated be sure there is just ONE vapor barrier(paper or plastic)on the LIVING side of the insulation. Multiple and/or reversed vapor barriers will cause moisture buildup in the sheetrock and no end of trouble!
Now the fix: If indeed the framing has shrunk, you do not need to take the otherwise undamaged sheetrock down(hooray)! Just take a saw(a dullish handsaw works great, but anything will do)and cut a kerf along the protruding joint lines, end to end and all the way through(the end jointss might be OK, leave them for now but keep an eye on them). The space thus created will allow for movement. Give it as much time as it takes for the framing to stabilize then retape/refinish the joints. I saw this happen just once in my 28+ years where a garage was trussed with wet yellow pine which had lain in the rain forever, and even the roof sheeting buckled as it dried out. I won't even go into the major warpage that occured there....
Keep your powder and your lumber dry!