The buildup of ghost marks can be caused by any combination of moisture, cold spots, static electricity, air currents, and a supply of dust, soot, and other particulates that can drift with the air.
Cold spots on walls and ceilings get damp from condensation, and air-borne dust clings to the dampness. In this situation, ghosts indicate studs, joists, wall headers, or even individual sheetrock screws, which are naturally poor insulators. The ghosts also reveal gaps in the insulation, which could be caused by dampness, mice, or poorly fitted insulation. Fixing these cold channels requires carefully determining the exact source of the leak and deciding on the most cost-effective method to plug it.
Too much moisture can be caused by overusing humidifiers, drying clothing on indoor racks, or leaving a stone foundation or dirt-floor cellar unsealed. Moisture can also be released into the air from propane log fires, unvented gas ranges, and kerosene heaters. Proper venting and more careful attention to indoor humidity can help. It also reduces the moisture that mold and mildew need to get a foothold.
On the other hand, too little moisture in the air can increase the buildup of static electricity, which charges the dust particles and makes them more likely to cling to walls, ceilings, and everything else.
Hot-air heating systems will also increase static by drying out the air and blowing it through the ducts, where friction causes the electric charge to build up. There’s a balancing act involved, and keeping your furnace cleaned and tuned can help.
But where does all that dust come from? A lot of the dust is soot and ash, and here the main culprits are smoking, woodstoves and fireplaces, poorly tuned furnaces, kerosene heaters, propane logs, cooking on unvented stoves, and even candles (particularly scented ones with soft wax). Cutting back on any of these will help reduce the soot load in your house.
Dirt comes in on firewood, shoes, clothes, pets, and also drafts that seep in around leaky windows, gaps in vent systems, alongside chimneys, and through any other small crack.
Use that hot-air furnace to help clean the air by changing its filter frequently. More frequent vacuuming also helps, as does wiping feet, cleaning welcome mats, and those other tidy-up chores your mother was always nagging you about. Using the vent fan over your stove will help reduce that source of soot and other particulates. Free-standing domestic air filters and “purifiers” can also help remove particulates that cause ghosting.
What About Painting?
It’s important to note that painting over ghost marks doesn’t work. You need to clean the walls and ceiling thoroughly so the paint will adhere properly. If moisture is the culprit, you must dry them out, too. But this is a temporary fix.
Even if the paint covers them, ghost marks will simply reappear over time unless the root causes are cured.
Of course, you could always try to color-match your paint to your ghost marks so no one will notice them, but the ghosts will still be lurking there, and you’ll still be living with all those cold spots, damp spots, sooty drafts, and dirty ducts. For your own health, it’s a good idea to get rid of ghosts by curing the root causes.
As a side effect, your house will look better, too!