Our house is vintage 1950, a post-war minimal traditional. After 60 years it has some sags.
This is actual sheet rock, not wallboard, not gypsum board, not plaster. It's like concrete, attached to the ceiling joists with nails. We have 2 rooms left with the stuff. The other sagged first and we've fixed it.
I've been supporting this one with 2x4's for a year. I'm a guy. I don't care. I could wait another year or 2.
I'm sure the proper thing to is rip down the ceiling and put up a new one. But it's way cheaper to screw the old one up there and camouflage the cracks and ripples with mud and flat ceiling paint. I mean, do you want a 60 year old house to look brand new?
Fortunately my son has been helping. Today the caulk.
He was wearing his "blacks" today, a sure sign of an artist.
This is a "If You Give a Mouse a Cookie" style project, if you get my meaning. David is obviously NOT caulking the ceiling.
P.S. This is an 8' 3" ceiling in a 178 square foot room