How to Clean Mold and Mildew

Aug 23, 2023

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These unwelcome fungi cling to any damp area. You must destroy them.

One of the most common and challenging problems facing homeowners today is how to deal with mold and mildew.

These tips will help eradicate mold and mildew from inside your home, but first, let’s discuss the differences and similarities between these two scourges.

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Mold and mildew are types of fungi, and each thrives in warm, moist environments, such as kitchens, bathrooms, basements, and crawlspaces. Mold is usually black or dark green, and it’s slimy and musty-smelling. Mildew is most often gray or white and has a powdery, fluffy texture.

Mildew typically grows on top of damp surfaces, so it’s easier to clean off than mold, which tends to grow into and behind surfaces, including walls and ceilings. There's also one other important difference: Prolonged exposure to mold can cause all sorts of health issues, including migraine headaches, respiratory failure, fatigue, joint pain, depression, heart problems and irritation of eyes and throat. Mildew isn’t nearly as invasive or dangerous as mold, but in some cases, exposure will cause respiratory and nasal irritation.

The good news? Most mold and mildew growth can be eliminated by first reducing excessive moisture, and then cleaning and killing the fungi with an appropriate cleaner.

Excessive moisture can be introduced into a home in several ways, including a leak, very high relative humidity, or inadequate ventilation. If you find mold growing on roof rafters or on the underside of the roof sheathing, then check for water penetration from a nail hole, or damaged flashing in a valley, around a chimney or where a sidewall meets a roof plane—and it doesn’t take much of a leak to promote mold and mildew growth; a surface just has to remain damp to support fungi.

Larger leaks, such as those caused by a busted water pipe or baseboard heater, can cause quite a bit of damage, especially to ceilings and walls. Mold and mildew will quickly flourish in dark, dank spaces, so it’s important to cut out and remove any water-damaged drywall and sodden insulation from between the wall studs and ceiling joists. Leave the wood framing exposed for a few days, so it can dry out. You can speed up the drying process with some electric fans.

During extended periods of high humidity, excessive moisture in the air can cause mold and mildew to grow on damp surfaces, including drywall, ceramic tile, fabrics, upholstery, and even wallpaper. The simplest ways to reduce high humidity is to run the air conditioning and use dehumidifiers.

⚠️Be sure the dehumidifier’s reservoir doesn’t over flow or it’ll flood the floor, creating a new moisture problem.

Also, have your air-conditioning system checked annually by an HVAC technician to confirm it’s operating properly and efficiently. An out-of-tune A/C unit can pump too much moisture into the house.

Another effective way to reduce moisture is to increase ventilation. This is especially important in today’s energy-efficient homes, which are almost airtight. A surprising amount of moisture is released into the air during many everyday activities, including cooking, showering, washing dishes, even exhaling. And if this excessive moisture isn’t moved out of the house, it can promote mold and mildew growth.

So, be sure to turn on the bathroom vent fan whenever you take a shower, and allow the fan to run for at least 10 minutes after showering. And check to be sure the fan’s ductwork runs to the outdoors; it should never simply blow hot, moist air into the attic.

Always use the kitchen range hood when cooking, including when boiling water. And, again, be sure the range hood exhausts to the outdoors. A re-circulating range hood, which simply draws air through a filter and then blows it back into the kitchen, is totally useless at removing moisture, smoke, and odors from your home.

Before you invest in a new dehumidifier, measure your home’s humidity levels with this cheap, quality thermometer and hygrometer.

This 70-pint dehumidifier is good for spaces up to 1,400 square feet and powerful enough for damp spaces with 50 percent humidity.

The highly-rated Pro Breeze is fitting for small spaces like a kitchen or bathroom, but its size makes it portable to move it wherever you need.

Plenty of AC units have dehumidify settings, but this LG 115V portable air conditioner can dehumidify up to 2 pints per hour.

There are several different types of mold-and-mildew removers available online and at home centers and hardware stores. Most of these cleaners work pretty well, just be sure to read the label carefully to confirm that you’re using the correct type. Some products are general-purpose cleaners, while others are specifically formulated for tub and tile surfaces.

However, you can make an effective, affordable cleaner with bleach, which has been proven to not only remove mold and mildew, but it also kills the spores to prevent it from growing back. Now, you can use regular liquid chlorine bleach to clean away mold and mildew, but I’d suggest using oxygen bleach powder instead. Oxygen bleach costs a bit more, but if you spill any on your clothing, carpeting or upholstery, it won’t bleach out the color. More importantly, though, oxygen bleach doesn’t evaporate nearly as quickly as chlorine bleach, so it stays on the surface longer and kills more effectively.

⚠️Be sure to wear rubber gloves and protective eye goggles when cleaning with any bleach product.

To kill light to moderate mold and mildew growth, pour one cup of oxygen bleach into one gallon of hot water. To remove heavy staining, use two cups of bleach to one gallon of hot water. Mix well until all of the bleach crystals are completely dissolved.

Pour the bleach mixture into a quart-size spray bottle, or for larger jobs, into a three-gallon pump-up garden sprayer. Saturate the mold and mildew stains with the bleach solution and then wait at least 30 minutes.

Next, use a nylon stiff-bristle scrub brush to scrub off the stains. Wait for the surfaces to dry, then check to make sure they’re clean. If you see even the smallest speck of mold or mildew, spray the area again and repeat the process.

Joe is a former carpenter and cabinetmaker who writes extensively about remodeling, woodworking, and tool techniques. He has written eight books and is a contributing editor to Popular Mechanics. He also appears on the Today’s Homeowner TV show, and co-hosts the weekly Today’s Homeowner Radio Show. Joe writes from his home in Roxbury, Connecticut.

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