Spread a drop cloth under the spot to be repaired. Scrape the area with a 4 or 5-inch wide drywall knife to remove the old texture and any paint that has worked loose.
Spray on the first coat of aerosol primer. Hold the can with the top of the can pointed toward the ceiling 12 to 18 inches from the damaged area. Use a ladder to get closer if needed. Depress the trigger and spray an even coat, working in short bursts, releasing the trigger between strokes. Work to cover the water stained area and feather the edges out to blend into the rest of the ceiling. Allow the primer to dry.
Examine the repair area for signs of stain bleeding through. It will typically take two or three coats to hide a water ring. Reapply primer, using the same technique. Keep the can moving to prevent drips.
Shake the can of popcorn texture vigorously. It requires a full volume of propellant to prevent clumping. Extra time shaking will prevent the need for reapplication.
Spray a light coat of popcorn onto the affected area. Keep the can 12 to 18 inches from the ceiling. Move in short strokes in a curving pattern for best results. Stand back from the work frequently to check for evenness.
Apply a second coat of popcorn, if needed. Allow the texture to dry overnight before applying the finishing coats of paint.
Paint the repair area with flat spray paint in white, or off white, depending on your ceiling. Test in a small area and allow it to dry for 15 minutes before painting the entire repair area. Apply the paint using the same technique as primer, with one exception--spray paint works best 8 to 10 inches from the surface. Work in short strokes moving across the repair area in a crisscross pattern to ensure complete coverage.