my 1924 spanish revival home has beautiful hand plastered ceilings and walls throughout. the living rm ceiling (18x12-14) has sagging plaster in two spots with an area of 1-2ft of sag around each. there are cracks as well outside the sagging areas. in the past there was a small water problem, now fixed. we've inspected the other side of the ceiling from the attic and know that the lath is fine. keys appear to have separated from the plaster although the keys remain in the lath. the sag is roughly .5 inch.
i would love to just re-attach the sagging plaster to the lath using plaster washers and screws but have read online that this kind of sag requires complete replacement of the ceiling with drywall. i've seen drywall repair of this kind in remodeled homes and can't say that it looks very good or authentic.
any advice welcome,