What Causes Black Spots on Walls?

Drywall Screws

• Drywall screws are specially designed with a black phosphate coating that aids in preventing erosion. Black spots that are uniform in placement and approximately 3/8 of an inch in diameter are likely the result of these screws beginning to wear down. If the problem is only in one room, it is possible that the breakdown is being caused by moisture, either excessive humidity, a leak, or an improperly installed air-water barrier if it’s an external wall. If excessive moisture is the problem, it must be dealt with before any corrective measures are taken against the black spots. A dehumidifier will remove excessive humidity, while removing the drywall and fixing the leak or moisture barrier will treat the other problems. Once the water has dried, replace the damaged drywall and screws. If moisture is not a problem, remove existing screws and replace them with new ones. Any remaining holes or damage is then covered with dry wall mud, primed and repainted.

Soot Stains

• A number of environmental materials can result in black stains along walls or ceilings. Soot from a fireplace or burning candle is a common source of staining and is often released into the air when the fireplace is in use. This material is likely to stick to drywall screws, studs and ceiling joists, since the temperature there is cooler than in other areas, according to Trained Eye Home Inspection. A thorough cleaning should be done, first with a vacuum attachment, then with a soap-and-warm-water solution applied with a sponge or cloth. For tougher soot stains, soot-specific sponges are available from most home improvement or hardware stores.

Nicotine Stains

• Nicotine from cigarette smoking is notable for causing stains on just about anything it comes into contact with, including walls and ceilings. Ordinarily, these stains are a dark brown color but could appear black with age. Removing these stains will require a process similar to removing soot -- vacuuming, soap-and-water scrub and, possibly, an additional cleaning with trisodium phosphate (TSP), which will remove stubborn stains. Repainting is done when this process has been completed and the stain is gone. Otherwise, the stains have a tendency to seep through new paint.

Mold

• Mold problems arise when conditions are optimal for colonization and growth, usually the result of high humidity, a water leak, or flooding where water is left standing for long periods of time. Basements and bathrooms, because they tend to be more wet and humid than other parts of the home, are prone to mold problems. The treatment for mold will vary greatly depending on the type of mold (not all black mold is hazardous) and the severity of the infestation. If the infestation is light, remove colonies with a warm water-and-bleach solution, and allow the area to dry thoroughly. More severe infestations -- particularly Stachybotrys mold -- will require the aid of a professional. Always wear eye and respiratory protection, long sleeves, pants and closed-toed shoes when dealing with mold. Most species cause a minimum of irritation to the respiratory tract, eyes and skin; however, exposure to some species causes more severe side effects, including breathing difficulty, memory loss and death. The source of moisture must be removed or repaired to prevent mold from returning.