How to Patch a Ceiling
How to put a fresh face on brown, blistered, water-damaged drywall
Score the Perimeter
Place a drop cloth beneath the work area, put on safety glasses, then use a utility knife to make a shallow cut around the damaged area. This cut helps to keep you from inadvertently stripping the paper face off the undamaged drywall during the next step.
Shown: TOH senior technical editor Mark Powers uses a utility knife to cut around the water damage on a drywall ceiling