This house was flipped in its history. Ceiling had popcorn removed and texture added, I think. Built 1978. In painting ceiling find it, or rather texture, is sagging about three nickel widths. What can I do to fix this? Area of sagging is in seven places, each less than six inches square, some smaller. Inject some kind of glue and hold up until it sets? Sagging is not noticable unless you push on ceiling.