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About This Project
What causes these dark stains on our cathedral ceilings? We’re tired of repainting every three to four years, so we’d like a better solution.
—W. Rhea, Indiana, PA
The phenomenon of dark stains running along the ceiling joists is commonly called ghosting. It’s generally caused by soot deposits from such sources as candles, cigarette smoke, poorly adjusted gas appliances, pilot lights and cooking grease.
The reason soot collects on the drywall along ceiling joists (generally during winter) is the temperature difference between the underside of the joist (which is cooler) and the space between the joists (warmer, because that area is insulated). This can cause a tiny bit of condensation on the drywall that is directly underneath the joist. Over time, this damp area traps dust and soot particles that eventually form what looks like a shadow.
Stopping the ghosting isn’t easy. You have to warm the ceiling, either by adding more insulation over the ceiling (usually difficult) or by improving warm air circulation, perhaps with a ceiling fan. In addition, we recommend that you reduce potential soot sources.
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