Brace the sagging drywall with lumber to hold it up and in place while you reattach it, if you don't have a partner to push the drywall up against the ceiling joists. Use an 8-foot piece of lumber (assuming you have a standard 8-foot tall ceiling) firmly wedged between the floor and ceiling.
Pound in protruding drywall nails or screws with a hammer. Try not to break through the paper covering the sheet of drywall.
Screw the drywall into the ceiling joists with 1 1/4 inch drywall screws, about 8 inches apart. You should be able to follow the existing seam; if not, use a stud finder (an electronic device that detects the location of joists or studs behind drywall) to locate the joists.
Place a level across the previously sagging section of drywall to see how flat you got it. If you still find low spots, put in some more screws--but be aware that the drywall may have permanently lost its shape and you'll never get it perfect without replacing it.
Fill the screw holes with two coats of joint compound, waiting 4 to 8 hours between coats for them to dry. Sand them smooth using a fine grit sanding sponge, or drywall sander and 180-grit sandpaper.
Texture the ceiling to match, unless it was smooth. Purchase spray can texture from a paint or hardware store--there are textures to match most ceilings, including orange peel and acoustic popcorn texture.
Follow the directions on the can for application and drying time.
Prime over all the repairs, and paint the ceiling. Plan on repainting the entire ceiling unless it was otherwise in very good condition, and you have the exact same paint that was used originally.
Things You Will Need
- 8 and 4 foot lengths of lumber
- Screw gun
- 1 1/4 inch drywall screws
- Stud finder
- Joint compound
- Texture material
- Prime the ceiling with shellac-based primer to cover brown water stains that resulted from a leak.
- If the ceiling is firm, but still sagging slightly between the joists, paint it with flat paint to disguise the unevenness.