You're a homeowner. One day, you notice some dark, shadowy lines appearing on your walls or ceiling. Your first thought might be mold, which is kind of scary. But if the lines clearly trace the framing behind the drywall, they're more likely to be evidence of a phenomenon called “ghosting” or “thermal bridging.” The good news is that while it’s unattractive, drywall ghosting poses no threat to your health, and there are ways to deal with it. But first you need to make sure it isn't mold.
Drywall ghosting occurs when you have insulation between the framing wood, which can result in a temperature differential—the drywall covered by insulation stays warmer, while the wood framing gets colder due to a lack of insulation. Then, your daily activities inside the house—showering, cooking, even breathing—produce warm air, which creates condensation on the colder spots of the walls or ceiling. Add in dust, airborne dirt, or soot from burning candles or other sources, and those damp, cold areas will start to develop into faint stains—ghosting.
A few things to keep in mind:
It’s important to note that you should test for mold if you see what looks like ghosting—while uncommon, it’s not impossible for mold to develop in a grid-like pattern on your walls or ceilings.
You should investigate your insulation as well—if the insulation in your walls or attic space was installed inconsistently, you can have random cold spots that can develop ghost lines that don’t adhere to the framing grid.
Another way ghosting presents is as circular stains above light fixtures: The heat from the bulbs can rise, find those colder spots on your walls, and combine with soot or dirt to form a ghost stain.
In general, mold tends to be more chaotic in its presentation, developing as more circular stains that don’t adhere to a grid or appear almost as “shadows” of light fixtures. And if the staining on your walls or ceiling is inverted—with dark spots on either side of the framing, leaving “clean” lines—that is more likely to be mold.
If you eliminate the possibility of mold, the great news is that ghosting is an entirely cosmetic problem. It poses no threat to your health. All you’ll need to do is clean the stains properly, prime, and re-paint your walls:
Scrub the walls with soap and water to get rid of the stains. You can utilize a soot sponge if the stains are stubborn, or use a magic eraser-style sponge.
Dry the area thoroughly.
Prime the entire wall or ceiling using a stain-blocking primer to ensure lingering stains don’t resurface. Wait for the primer to dry thoroughly, then re-paint.
It’s important to note that if you don’t address the underlying cause of ghosting on your drywall, it’s going to happen again even after you clean and paint. That could mean adding insulation to your attic or walls and eliminating sources of soot or other dirt in your home. You can also try lowering the indoor humidity of your home to reduce the sources of moisture that cause condensation.
Drywall ghosting might be initially alarming, but is pretty harmless. Unless those faint lines re-arrange themselves into messages, in which case you should move out immediately.
