Ghosting on Walls and Ceilings: What is it and What to Do About it?

Oftentimes, inspectors and contractors will receive phone calls from homeowners who describe a mold problem that has recently developed on the walls and ceilings of their homes. Usually, they describe the mold patterns as black stains or spots on the walls and ceilings that seem to follow the framing of the house.

The good news for these homeowners is that the stains are usually not mold and they are unlikely to present a health hazard to the occupants or a structural hazard to the building. The problem they are describing is called “ghosting” or “thermal bridging.” While this issue is not harmful, it can be a nuisance.

If you’ve noticed this unusual staining pattern in your home, it is helpful to understand why ghosting on walls and ceilings is happening and what can be done to correct it.

Understanding the problem of ghosting on walls

To visualize thermal bridging, let’s think about a home in the wintertime – say you own a house in Denver, CO. You are inside your cozy warm space cooking, cleaning, breathing, and showering – all of which create humidity inside the home. You might also be burning candles, incense, or wood for a fire. In the winter, the insulation in your house, if it is doing its job, will help keep the cold out and the warm in. Insulation is installed in the stud bays inside the walls and on the floor of the attic. The limiting factor for most insulation is that it does not cover the wood framing of the building, just the empty spaces between the framing.

Ghosting happens when mildly damp, warm, and possibly sooty interior air condenses on the sections of walls and ceiling that are colder because part of the wood frame is uninsulated. This results in black sooty stains on your walls and ceilings that follow the patterns of your home’s framing. Sometimes stains can even reveal nails in a wall because the metal is more prone to becoming a condensing surface. Typically, the amount of condensation is not enough to cause a mold or structural problem, but it does create irritating lines on your walls and ceilings. So, how do you fix this?

Steps to repair ghosting and black stains

The first step you need to take to stop ghosting on walls is to eliminate indoor air particles. Stop burning candles, firewood, or incense. The next step is to monitor the relative humidity inside the house. Buy an inexpensive humidity and temperature meter and try and keep your indoor humidity below 55 percent during the cold winter months. You can typically do this by turning on bath fans, which will have a drying effect on your home as you vent out moist warm air and replace it with dry cold air. Finally, you will need to use stain-killing paint to seal up the stains and repaint the walls and ceilings. 

If you see the staining developing in larger patterns on the wall or ceiling, in places between the framing, this indicates the wall or ceiling is likely not insulated correctly. Unfortunately, the only fix is to open up the wall or ceiling and insulate it properly.

What if the black stains are actually mold?

If you call a professional and determine that the black stains are actually mold, you have a few options depending on how severe the mold is. Regardless of what you do, it is essential that you contact an expert to assess the situation and determine the health risks. Once you’ve done so, you can call in a cleaning company, which will scrub the infected area down with special detergents and cleaning agents. Or, if the mold is less severe, you can create a mixture of cleaning agents and scrub the mold yourself. To do this, follow the steps below:

• Create a solution that is 1/4 bleach and 3/4 water.
• Thoroughly soak the affected areas of the wall until it is saturated with the solution.
• Let the solution soak into the affected areas for 5-10 minutes.
• Scrub the affected area with a brush until the mold stains are removed.
• Repeat until stains have been cleansed.

How can I prevent mold from forming?

To prevent mold from forming, check out the following tips:

• Make sure to run your bathroom’s fan while bathing and after to prevent moisture from accumulating. If possible, shower with the door open to encourage circulation and proper ventilation.
• Mop up any significant spills from water or other liquids quickly.
• Use mold-resistant paint in bathrooms and other rooms where there is significant moisture.
• Clean your bathroom frequently.

So, the next time you notice black stains in your own home or in homes on the housing market you are considering purchasing, don’t panic. Contact a local inspector or contractor with a specialization in mold removal and they can help you determine the severity and extent of the problem, whether it’s ghosting on the walls or mold.

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