Many traditional and classical styled homes have thick, swirled plaster ceilings in dining and other formal rooms. Occasionally, these and other less formal plaster ceilings experience water damage, either from a leaking roof or a water pipe above the damaged ceiling. Once the water leak has been fixed and the area has dried out, a large discolouration is often visible. Painting over the stain may not always fix the problem.
Position a ladder beneath the damaged area of the ceiling in the area. Touch the plaster. If you feel a temperature or textural difference between the discoloured area and a nondamaged area, the plaster may still be wet.
Apply gentle finger pressure to see if the plaster is sagging or pulling away from the ceiling. If plaster is going to fall off the ceiling, hire a qualified plaster repair company to reattach the plaster and rebuild the pattern.
Sweep the damaged area with a soft brush to remove any loose paint or debris. If the plaster looks and feels hard, and you're able to clean up the plaster with the soft brush, it's likely the plaster is dry and the damage is contained.
Apply a coat of quick-drying, oil-based stain blocker. These types of stain blockers come in spray, invertible and liquid forms. The invertible can allows you to spray upward. Apply at least two coats to the damaged area and at least several inches in each direction. Allow each coat four hours to dry.
Paint the entire ceiling to unify the paint colour. If the ceiling was newly painted when the damage occurred, you may have existing paint to touch up the stained area. If choosing a new paint, make sure it's compatible with the stain blocker or existing paint.
Some stain-killing primers dry as a bright white colour. If your existing ceiling paint is old, the new primer will stand out as much as the stain.