Covering stains on a popcorn ceiling can be difficult. The textured material that was sprayed on the ceiling years ago may fall off in pieces if you touch it with a roller or brush. It is even more likely if there has been water damage. Make sure that underlying water leaks and wet materials have been fixed, or like a perennial plant the stain could grow back. Simply painting over a stain might look good for a while, but it could start to show through again. Popcorn ceilings applied before the early 1980s may contain asbestos, so have it tested before you start.
Step 1 - Prepare Yourself and the Room
The job is going to be messier than you may think. Bits of the popcorn ceiling will probably fall off. It is wise to wear eye protection, a face mask, and possibly a hat. Move furniture to a safe distance or cover it. Put drop cloths on the floor. Mask off walls or light fixtures that are near the stain.
Step 2 - Cover the Stain With Stain Blocking Primer
Stain blocking primer comes in spray cans or in a paint can. Spraying works in small areas, but for a larger area, it is a good idea to roll it on. The roller should be a type that gets the primer into all the nooks and crannies of the textured ceiling. Give it a second coat if you can still see the stain after it dries. The primer may be the right color to blend in with your ceiling. If so, leave it to dry and enjoy your stain-free ceiling.
Step 3 - For Large Areas, Use an Airless Sprayer
If you rented an airless sprayer, spray the stain blocking primer with the nozzle about 12 inches from the ceiling. Let it dry overnight, and give it another coat.
Step 4 - Repaint the Covered Area
If the ceiling was painted before, you will need to repaint the section where the stain was. Let the primer dry, then roll on your new paint, or use your sprayer. Use an oil-based or acrylic paint. Popcorn texture absorbs water-based paints, ultimately requiring much more paint.
WARNING: Keep your safety glasses and face mask on while you use the paint sprayer.