Sometimes identifying mold is obvious, other times not so much. Here's what to know about it, and how to find it in your home.
13 Tips to Help Identify and Prevent a Mold Problem in Your House
Updated on Nov. 27, 2024
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Look for Visual Signs of Moisture
If you have plumbing leaks or water damage, mold is sure to follow. Beyond looking for the obvious, like dripping pipes, also check for bubbling paint, ceiling water stains, damp basement walls and discolored patches on walls, ceilings and floors.
A common mistake is not noticing small spots, which may be signs of a much bigger problem lurking behind the drywall, says Maria Anderson, a cleaning and mold expert at Henfield Storage.
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Do a Smell Test
It’s not the most accurate way to find mold, as everyone interprets smells differently, but if you sense a musty or earthy odor in your home, it can be an indicator that something is amiss.
“A homeowner generally has an acute sense of when something is out of the norm for their living space,” says Vent. “If that odor is getting more noticeable over time, it can be a sign that something may be going on.”
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Look for Condensation
If your exterior windows or walls sweat or collect condensation, it could be a sign that your home is too humid, and thus has prime conditions for mold growth.
“These indicators may not seem like a huge deal when you first identify them, however they are a sign that you have a more universal, atmospheric problem going on, and if not rectified, could lead to a more serious problem,” says Vent.
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Use Bleach to Determine if It’s Mold or Dirt
Sometimes mold looks like dirt. One way to tell the difference is to dip a cotton swab in diluted bleach (1 part bleach, 16 parts water) and dab it on the wall. If the spot lightens after two minutes, or keeps coming back after cleaning, it’s probably mildew or mold. If the area remains dark or wipes off and doesn’t return, you probably have dirt.
However, it’s not a sure bet, because it doesn’t work for all mold species or on all surfaces, says Bethany Uribe, a building inspector at ASAP Restoration.
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Use a Moisture Meter
To identify areas with excess humidity that could foster mold, such as walls and ceilings, use a moisture meter or thermal imaging. Readings above 20% definitely mean you have a problem, says Anderson.
Pay close attention to spots near windows, under sinks and other areas where condensation can build up, says Erwin Miciano, owner of Semi Homes. “Doing a thorough check of these places can save you a lot of hassle down the road,” he says.
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Buy a Mold Test Kit
You can buy DIY mold test kits online and in most home-improvement stores. They typically come with a Petri dish that collects spores from the air, and are most effective when placed in areas that are most likely to have moisture, like bathrooms, kitchens and basements, says Miciano.
“One mistake I’ve seen people make is assuming that one or two tests are enough,” he says. “If your home has multiple stories or areas that have been exposed to leaks, you should test those areas as well to get a clear picture of the issue.”
Beyond testing for mold in the air, you can test for mold on surfaces. Again, DIY test kits are available online and in most home-improvement stores, or you can send samples to a professional lab for testing, which is what Uribe recommends.
“A DIY test won’t be the worst, but it isn’t made for accuracy,” she says. “Basically, it all comes down to peace of mind. If you are seeing a black fungus-like growth stretch across a wall that you know just got flooded, odds are strong you know already that it’s mold, and you won’t need to have it tested, just removed by pros.”
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Hire a Pro to Test for Mold
Professionals can perform a “scrub test,” which essentially collects mold spores by pulling air through a vacuum with a filter attached. These give a more accurate assessment than the DIY air test kits, especially since the samples are sent to a medical lab for testing.
“This is an extremely effective way to test for mold spores and their quantities in a given area,” says Uribe. “Most outline every single species of mold spore cataloged, and also how much of that spore was collected, to indicate if they are in the red zone for health concerns.”
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Check Your HVAC for Mold
HVAC ductwork can harbor mold, especially when it’s in the attic or not properly sealed. To prevent mold in your air ducts, have them periodically examined, serviced and cleaned. If mold forms on the ceiling under a duct or register and there’s no sign of a roof leak, badly insulated ductwork may be the cause.
Also, “The hot air in the attic and cold air in the ductwork during the summer can cause condensation in and around the ductwork, which can grow mold,” says Chad Thielk, a home-improvement expert with JustAnswer.com. “This is where an air test can help you identify elevated mold in the air.”
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Probe the Area with a Screwdriver
Mildew is a surface type of mold that won’t damage your home’s structure. But other types of mold cause rot. To check for that, probe the suspect area with a screwdriver or other sharp tool. If the wood is soft or crumbles, the fungi have taken hold and rot has begun.
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Monitor Your Air Quality.
Some air quality monitors can measure the concentration of mold spores in the air, which can help you determine if you have hidden mold in your house.
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Look for Leaks Outside
If mold is growing on an exterior wall or ceiling, look for a leak in the wall or roof. Measure from the moldy area to a reference point like a door, then find the spot on the other side of the wall or ceiling.
Closely inspect nearby vents, roof flashing, decks, window wells and anywhere wood is rotting. Look for ground sloping toward the house and downspouts emptying next to the wall. If the ground around the house gets too wet, moisture will wick into the foundation or slab and become persistent dampness. Make sure you properly install flashing when you’re fixing the leak.
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How To Prevent Mold
Mold particularly thrives in environments above 55% relative humidity, so to help keep mold at bay, monitor humidity levels, especially in basements, says Vent. He also recommends:
- Regularly checking plumbing for leaks,
- Watching for window condensation,
- Checking your attic annually,
- Keeping your HVAC built-in humidifier set below 55% relative humidity,
- Running a dehumidifier in your basement,
- Regularly changing your furnace filter;
- Checking downspouts and gutters for functionality; and
- Ensuring your basement grading is pitched away from the house, especially near garden beds and other landscaping.
Also, keep up with cleaning in general. “This may sound obvious, but the cleaner your space the better,” says Vent. “Home hygiene can be a great deterrent for mold growth.”
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FAQ
Can you test for mold in the air?
Yes, you can test for mold in the air. There are DIY kits which sample for mold in the air. However, professional sampling, known as a “scrub sample” is more accurate. Those use a vacuum, which pulls air through a filter, and is sent to a medical lab for testing.
“As a home inspector, if you think you have mold but cannot see it, I say you should definitely call a pro to have an air sample taken,” says Thielk.
How much does a mold test cost?
High-quality medical-grade lab testing usually costs between $300 to $600. DIY kits start around $35.
When should you call a pro?
If the mold is on the surface, you can probably just wipe it off with soap and water, says Uribe. Don’t use bleach, as mold isn’t affected at all by it, and some mold can actually eat bleach.
However, “if you spot mold on the backside of a piece of baseboard that you just pried away from the wall, and it’s in a spot that you know just got flooded, then you are in for a fantastic fungus ride, and if you don’t call the professionals, you may be held negligent by your insurance company,” says Uribe.
Other scenarios where it’s time to call a professional:
- You suspect mold is affecting your health;
- You have serious mold sensitivities, asthma or a compromised immune system;
- You have children or elderly in the home;
- You have cleaned the mold, and it has returned;
- The affected area is more than 10 square feet (otherwise you risk spreading it via the air);
- You just don’t feel comfortable dealing with it.
“From my experience, if there’s any doubt about the extent of a mold issue, it’s always better to bring in a pro,” says Miciano. “You don’t want to risk your health or the safety of your property by cutting corners. I’ve also seen firsthand how critical it is to catch issues early.”
About the Experts
- Russell Vent is Vice President of Paul Davis Restoration of Greater Rochester, NY, and a state-licensed mold remediator with more than 16 years of experience in both residential and commercial situations, including hospitals.
- Bethany Uribe is an AHERA certified building inspector at ASAP Restoration in Mesa, Arizona. She has nearly a decade of experience in the construction and water damage mitigation industries.
- Chad Thielk is a third-generation construction worker. He started in the industry at age 15 and worked for a commercial remodeling company before becoming a home improvement expert with JustAnswer.com, the on-demand platform for 24/7 help from pros.
- Erwin Miciano is a real estate investor and owner of Semi Homes, which specializes in direct-to-seller home buying transactions in Southern California.
- Maria Anderson is a cleaning and mold expert at Henfield Storage in England.
