How to Remove Mold From Inside Walls

Mold inside your walls is a sure sign of moisture intrusion. Mold also leads to the deterioration of insulation, studs, and drywall. Some types of mold can be hazardous to your health. And for anyone thinking of selling their home, mold in the walls will undoubtedly show up on the inspection report. 

Mold remediation in walls is a relatively simple, though messy, project that can stretch for a week or two. Because of this and because of safety concerns, many do-it-yourselfers decide to hire a professional mold remediation company.

7 Common Signs Mold Is Inside Your Walls

Musty Smell

Mold has a musty smell often compared to wet cardboard, wet pets, or an old house’s basement.

Visible Mold

Mold inside walls often stays within the walls. But when it does migrate to the drywall paper, wallpaper, paint, or baseboards, it appears in patchy clusters of small spots. Mold can be black, white, gray-green, or gray-brown.

Dampness

Walls might be temporarily damp from the use of a shower or from cooking. But if they are permanently damp and there is no apparent moisture source from within the room, it’s likely that the drywall, insulation, or studs inside are wet.

Soft Drywall

If the drywall is mushy, flakes away, or indents under your touch, it is probably wet. If the drywall is wet, it will most likely be moldy, too.

Stains

Dark stains on walls usually indicate previous or current dampness within the walls.

Previous Flooding

If flooded water has come into contact with the walls, it’s almost certain that mold is growing in the walls.

Poor Health

Not all mold is toxic and not all people are susceptible to the effects of mold spores, though they can lead to various negative health effects.

How to Check for Mold Inside Your Walls

1. Locate the center of the area most likely to have mold inside.
2. Shut off power to the area at the electric service panel.
3. With a pencil and straightedge, lightly mark a square approximately 6 inches by 6 inches.
4. Cut along the outline with a drywall jab saw.
5. Remove the cut-out and inspect its back for mold.
6. If there is no insulation in the wall, look at the back wall. Also, hold a small mirror inside and shine a flashlight on the mirror to inspect the back of the drywall.
7. If there is insulation, any mold on the drywall or studs will have spread to the insulation. So, the presence of mold on insulation usually means mold on other building materials. 

When to Remove Mold From Inside Walls

Unlike some other types of deterioration around the home, there is no acceptable level of mold in your walls and no waiting period. Once you discover mold, it’s best to open up the walls and remove the mold as soon as possible.

Mold can spread and affect other areas of the walls, insulation, ceiling, flooring, studs, and joists. The longer you wait to remove the mold, the longer mold has to grow.

Before You Begin

Removing mold from inside walls is a four-step process: removing moldy drywall and other materials; killing mold; encapsulating remaining mold; and rebuilding part or all of the wall with new drywall, insulation, and other building materials.

• Removal/Disposal: Moldy drywall and insulation must be removed. None can be reused.
• Kill Mold: Spray the mold with a liquid biocide to kill it. Alternatively, exposing the mold to air and light for long enough will kill it. Do not use household bleach.
• Encapsulate Mold: Cover the mold with a fungicidal mold encapsulant. Choose a coating that contains the active ingredient calcium hydroxide. Do not use ordinary house paint.
• Rebuild: The area must be rebuilt with new building materials. New insulation is added to exterior walls (interior walls do not require this). Drywall is hung, then painted. For areas with persistent mold, you may even choose mold-resistant drywall.

Safety Considerations

Wear NIOSH-approved breathing protection, disposable gloves, and coveralls or old clothing that you can wash at the end of each day. Double-bag the moldy debris in large plastic contractor clean-up bags. Avoid carrying the bags through the house; drop them out of windows if possible. If your area regulates the disposal of moldy debris, do not place the bags in the regular municipal trash run. Instead, check with your city for transfer stations designated for this type of trash.