DEAR BARRY: I painted the inside of my home only six months ago, and already it needs to be repainted. Portions of the walls have become visibly darkened. Strangely, this occurs wherever there are framing members behind the drywall. I can see where all the wall studs and ceiling joists are located. Not only that, I can see dark spots where all the drywall nails are located. What could be causing this, and what can I do about it? –Bill
DEAR BILL: What you are seeing is a phenomenon commonly called “ghosting.” When ghosting occurs, extremely fine soot particles in the air collect on the walls and ceilings at locations where the temperature is cooler and where there is higher electrostatic attraction.
Cooler temperatures occur at the framing members on exterior walls because the studs are exposed to the outside veneer of the building, and at ceiling joists because they are exposed to the cold air in the attic. Electrostatic attraction occurs at the framing members because the moisture content in the wood is typically higher than that of the drywall. And the drywall nails, being made of steel, also have a high degree of electrostatic conductivity.
If you paint your home again, the ghosting will reappear unless you eliminate the source of the soot particles. Soot typically comes from fireplaces, furnaces and other fuel-burning fixtures that are not venting properly. The fixtures themselves may be defective, but low air pressure in energy-efficient homes is another common cause. Some buildings are so well sealed that low air pressure can occur when exhaust fans are in use. This can adversely affect the venting of combustion exhaust from fuel-burning fixtures.
If you live in a high-efficiency home, you may need to compromise some of its air-tight characteristics by providing some exterior ventilation. For an evaluation of your specific situation, you should consult with an indoor air-quality specialist. Your local gas company may even have consultants who provide this kind of service and advice.
You should also have your gas fixtures checked by the gas company to be sure that there are no safety issues with the venting of exhaust.