Mold on Walls

Discover the common causes of mold on walls, and learn how to prevent mold growth in your home.


A detail shot of mold climbing up the corner of the wall.

Photo by: beti gorse

beti gorse

A detail shot of mold climbing up the corner of the wall.

By: Sean McEvoy

Mold on walls is a common problem for homeowners, particularly in damp, humid areas like basements, crawlspaces and bathrooms. You can take steps to identify problem areas and prevent mold on walls and mold in walls — and if your home is already affected by mold growth, you can address the problem with various mold removal products.

Hallmarks of a Healthy Home

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Healthy Living

Your personal health is directly related to your home’s health. For example, poor indoor air quality, a major symptom of a "sick" building, can indicate larger problems with dust, insects, chemical contaminants and mold — and produce a range of acute and chronic illnesses in humans.

To keep your home healthy, it's important to understand the hallmarks of a healthy home and the threats that can jeopardize it — and your own well-being.

A Healthy Home Is Organized

It's important to have a system to keep track of medicines, cosmetics, pesticides, cleaning chemicals, fire tools (candles, matches, lighters) and toxic substances.

You should know what you have, where it is and who can get to it.

"Label reading is a really good skill," advises Meri-K Appy, president of Safe Kids USA. "Based on my 30 years in this business, those words of caution — flammable, danger, caution, hazardous, keep out of children’s reach — come from someone's tragedy."

An organized garage is a safe garage. Tools that are heavy, sharp or powered should be hung up (or locked up) so they won't fall or be within the reach of children.

A Healthy Home Is Dry

Water may be the source of life, but too much of a good thing can have terrible consequences for a home, including molds, mildews, bacteria, insects and structural rot that can trigger allergies, headaches or asthma.

"Condensation or slow leaks inside walls are particularly insidious because they occur sporadically over a long period," says Carl Grimes, president of the Indoor Air Quality Association. "You often can't see or smell anything without opening up the wall and by then you might already be experiencing health problems."

The goal is to prevent moisture intrusion from top to bottom: cracks and holes in the roof and siding where rainwater can get in, plumbing leaks and poor drainage and groundwater runoff. The EPA recommends a relative humidity of 30 percent to 50 percent for home interiors, so good ventilation is a must.

It's also important to install the proper moisture barrier or retarder for your climate and housing type. If things get wet — and they will — they need a way to get dry.

A Healthy Home Is Ventilated

Proper ventilation protects you from unhealthy indoor air pollutants, including chemicals, combustive gases and biological contaminants, and protects your house by removing excess heat and moisture. Signs of inadequate ventilation include stuffy air, moisture condensation on cold surfaces or mold and mildew growth.

The Home Ventilating Institute, a nonprofit association that represents the manufacturers of residential ventilating products, recommends three ventilating strategies: intermittent local ventilation such as exhaust fans for bath, kitchen and other moisture-, odor- and contaminant-producing areas; continuous whole-house ventilation to remove stale, polluted air and distribute fresh, outdoor air throughout the house; and attic and crawlspace ventilation.

A Healthy Home Is Clean

Keeping a home clean — specifically, free of dirt and dust — improves indoor air quality, helps control mold and pests and prevents disease.

Scientific studies suggest that the world is getting dustier and a lot of the dust tracked into our homes is contaminated with arsenic, lead and DDT. Dust also provides food for mold, insects, rodents and dust mites.

Dirty or leaky heating and cooling ducts spread dust, particulates and mold spores throughout the house.

A Healthy Home Is Pest-Free

According to the U.S. Surgeon General, studies show that more than 82 percent of U.S. homes have detectable levels of dust mite or mouse allergens, while 63 percent have detectable levels of cockroach allergens.

Besides being revolting, cockroaches, rodents and dust mites (or more accurately, their droppings) spread disease and cause allergies, trigger asthmas attacks, contribute to poor indoor air quality and undermine the structural integrity of your house. Infestations are typically a sign of a bigger issue: a poorly sealed house, rotting wood, mold and water damage.

If critters do make themselves at home, look first to nontoxic extermination strategies: Most pesticides can be harmful to people. The U.S. Green Building Council points out that "toxins from pesticides and baits can leach into soils and contaminate water or disrupt local ecosystems. Pests play a role in the food chain and are vital to keeping other wildlife in your neighborhood healthy and thriving. Your pest-control goal should be keeping vermin out of your house, not doing away with them completely."

A Healthy Home Is Nontoxic

Many building materials and home products contain or off-gas toxic substances. Indoor air pollutants range from combustion byproducts and biological contaminants to man-made chemicals and volatile organic compounds (VOCs). Many of these hazards are impossible to detect without special testing or equipment. Getting a professional evaluation can be invaluable: Exposure to certain toxins can trigger such ailments as headaches, fatigue, asthma and even – in the case of asbestos, benzene, formaldehyde and radon – cancer. You can minimize your risk by using low-VOC building materials, installing proper exhaust and ventilation systems, fixing moisture issues and using "green" cleaning products. Hire EPA-certified contractors to abate problems like asbestos, radon and lead.

A Healthy Home Is Structurally Sound

Things big (natural disasters) and small (careless workmanship) can undermine a structure’s integrity. Whether you have a newly constructed home or one that's been repaired or renovated, check for joists that have been cut or installed improperly and load-bearing walls that have been compromised.

"A hairline crack that's diagonal in a wall or foundation is normal," says Kurt Salomon, president of the ASHI. "Cracks that are horizontal or more than a quarter-inch wide are bad."

In other words, total settlement (a fairly even, virtually undetectable sinking effect) is tolerable but differential settlement (think Leaning Tower of Pisa) indicates a problem such as loose soil or poor drainage around the foundation. Check basement walls for wet spots or efflorescence (salt bleeds from wet concrete), keep gutters clear and point downspouts away from the house. If you have a leak or flood, use heaters and fans to thoroughly dry affected areas, particularly inside wall cavities, and replace damaged materials.

A Healthy Home Is Free of Combustion Byproducts

Fuel-burning furnaces, water heaters, stoves and cooktops all produce dangerous fumes that are byproducts of combustion. These include carbon monoxide, sulfur oxides, nitrogen oxides and soot, which can cause serious health problems or even death.

To reduce exposure, make sure furnaces, water heaters and fireplaces are in good working order and vented to the outside. Stoves, ovens and cooktops that burn fuel must be equipped with exhaust fans that vent the combustion byproducts to the outside.

Be sure to open flues when using fireplaces. Choose properly sized wood stoves — with tight-fitting doors — that are certified to meet EPA emission standards. And if you have an attached garage or oil/gas appliance (furnace, water heater or stove), you need a carbon monoxide detector.

A Healthy Home Is Maintained

Putting off seemingly small repairs can lead to serious accidents. If you notice a socket sparking or a lamp flickering, call an electrician to see if the wiring is shot. On stairs, fix loose top railings, balusters and treads. Your annual maintenance checklist should include inspecting chimneys, roofs, furnaces and water heaters.

Be especially proactive about water intrusion, starting with the exterior. Make sure rainwater is diverted away from the house and gutters are free of debris. Check for wood rot on sills and window casings, cracked clapboards and bricks and missing shingles. Inside, check plumbing connections to make sure they’re tight. If a toilet rocks, replace the wax ring.

A Healthy Home Is Comfortable

If you're not comfortable in your home, something is wrong. What is it about your home that bugs you? Do you often wake up feeling tired or stuffed up? Are there places in your home that you avoid because they’re too hot, too cold, dirty or dangerous?

Comfort is a barometer of such key components of a healthy home as indoor air quality and safety. For example, if you’re cold, you’re less inclined to ventilate. If the air is dry, you might humidify to the point of producing mold.

Paying attention to your comfort level can help you detect issues — indoor air pollution, excessive moisture, toxic chemicals and structural deficiencies — that may undermine your health and that of your home.

One of the most likely places for mold on walls in the home is in the basement. Because basements often retain moisture and humidity and can be susceptible to foundation leaks, they're prime areas for mold, which needs only oxygen, moisture and organic material to survive and thrive.

In particular, basements with old or exposed drywall can be at risk for mold on walls. Paper-coated drywall can be an optimal place for mold growth, as the organic material perfectly suits mold as a food source.

If you suspect that you have mold on walls or mold in walls in your home, there are several steps you can take to remedy the problem. First, remove all mold-covered debris, including drywall, insulation, sub-flooring and carpet. Next, you can use commercial products that contain ammonia or bleach on any hard surfaces affected by mold. Remember to wear a respirator or mask rated for mold spore exposure during any mold removal.

If you encounter mold on walls in bathrooms or showers, there's an easier solution: vinegar. Regular applications of vinegar or a borax and water mixture should keep walls in your shower and bathroom mold free.

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