How To Get Rid Of Mold On Concrete Block Walls

Mold. It’s unsightly, it’s smelly, and it’s potentially dangerous. That’s why, the moment you see it in your basement or around your property, the first thought in your head is usually figuring out how to get rid of mold on your concrete block walls.

Several approaches work well when it comes to getting rid of mold on concrete block walls. Hydrogen peroxide and vinegar are solid choices if you prefer to limit chemicals. Bleach is incredibly effective if the concrete is sealed. However, those aren’t the only options.

Which approach is best for your mold issue can depend on several factors, too. If you need to figure out how to get rid of mold on concrete block walls, here’s what you need to know.

How To Get Rid Of Mold On Concrete Block Walls

Why Does Mold Grow on Concrete Block Walls?

It may seem like concrete blocks aren’t hospitable to mold, mainly because there isn’t a clear food source. However, the ideal growing conditions for mold can often exist on concrete block walls, particularly if they’re exposed to the elements and aren’t regularly cleaned.

Concrete block walls readily absorb moisture, creating the somewhat damp environment that mold favors. If the surface is regularly exposed to rain, there’s a lack of drainage, the humidity is high, or there’s a plumbing leak, water absorption typically occurs.

While the material in concrete block walls doesn’t act as a food source for mold, dust and contaminants that rest on the surface can fill that role. As a result, mold can spread surprisingly quickly on concrete block walls.

What Type of Mold Grows on Concrete Blocks?

Multiple types of mold can grow on concrete blocks, suggesting the conditions are right. That includes various green, white, yellow, and black mold varieties. However, black molds are often what homeowners find.

It’s important to note that each mold color isn’t a single type of mold. Instead, several kinds of mold can appear similar if judged on color alone. Black mold is a prime example. While there’s a toxic version, other versions don’t pose that same level of risk.

However, any mold can be potentially dangerous, particularly to those with allergies, asthma, or certain other lung conditions. Similarly, it can cause skin, eye, and throat irritation, even if the mold isn’t considered overly hazardous.

Is Mold on Concrete Block Walls Dangerous?

As mentioned above, mold on concrete walls can be dangerous, though the degree may vary. Toxic black mold is especially hazardous because it can release mycotoxins, harmful substances that can impact the health of people and pets. With long-term exposure, the danger often increases, so mold in any home should be handled quickly.

While other molds don’t come with the same level of risk, that doesn’t mean they’re inherently harmless. Those with allergies, asthma or certain lung conditions may experience trouble breathing if there is mold present. In rare cases, mold can even trigger anaphylaxis.

Additionally, mold can irritate any person or pet, even those without allergies or pre-existing lung-related conditions. Often, that leads to discomfort in the eyes or throat or skin irritation.

Since that’s the case, most people should get rid of mold as quickly as possible when it’s spotted. That way, any potential harm can be mitigated.

It’s important to note that white discoloration that resembles mold may be efflorescence. Efflorescence occurs when water in the concrete evaporates, leaving behind salt and other minerals. While unattractive, efflorescence doesn’t pose a health risk. However, if you dislike the look, you can clean it away.

How to Get Rid of Mold on Concrete Block Walls

How to remove Mold from Concrete Block Walls

When it comes to how to get rid of mold on concrete block walls, several approaches are viable. However, they all have one step in common: putting on personal protective equipment (PPE).

Even molds that aren’t toxic can be irritants or allergens. As a result, you’ll want to wear an N95 mask, gloves, and goggles, at a minimum, when cleaning up mold. If there is a lot of mold, you may want to invest in disposable coveralls. That way, you can protect your clothing.

Additionally, most approaches will require similar equipment. You’ll need a stiff-bristled nylon or rubber brush regardless of the cleaning strategy you use. If you’re mixing up a cleaner, you’ll also need a spray bottle.

If you have a shop vac with a HEPA filter, that can make a smart addition, too. With that, you can vacuum the surface of the wall to remove some of the mold spores. However, if you don’t have access to a suitable shop vac, it isn’t technically a necessity.

Otherwise, any of the approaches below are often effective for getting rid of mold on concrete block walls. Either choose one based on what you have available or use personal preference as a guide.

1. Hydrogen Peroxide

Hydrogen PeroxideThis is one of the simpler options, as it doesn’t require any mixing. Simply take some 3% hydrogen peroxide and pour it isn’t a spray bottle.

Next, spritz the surface of the mold until it’s saturated.

After saturating the mold, let it sit for 10 to 20 minutes. Then, take your stiff-bristled brush and start scrubbing.

Once you’re done scrubbing the mold, rinse the concrete blocks with warm water. Then, dry the area with a towel.

2. Bleach

BleachIf you have a sealed concrete block wall, a bleach mixture can be an excellent option for cleaning mold. Add one cup of bleach to one gallon of water and stir to combine. Next, pour the mixture into a spray bottle for easy application.

Saturate the mold and let it sit for about 10 minutes. Then, scrub the wall with the stiffed bristled brush and, once the mold is removed, rinse the wall with warm water. Finally, towel dry the area.

3. Vinegar

VinegarWhile vinegar doesn’t kill every type of mold, it works quite well on some. Additionally, since it’s a natural cleanser, some people may prefer it. Usually, it’s best to do a test spot to see if it will work on your type of mold first. With that, you can simply apply some full-strength white vinegar to a small area and see if it conquers that bit of mold in about an hour.

If your test spot goes well, pour undiluted white vinegar into a spray bottle to ease application. Spray the mold liberally and then let it sit for one hour. Then, use the scrub brush to get rid of the mold and follow that with a warm water rinse and a towel dry.

For stubborn spots, you may want to use a two-fold approach. Get a second spray bottle and create a water and baking soda mixture. Usually, around four tablespoons added to a spray bottle of warm water is enough.

Then, saturate the mold with vinegar, letting it sit for an hour. After that, spray it with vinegar again, and follow that up with the baking soda mixture and scrub. Keep alternating between vinegar and baking soda until the mold is gone. Finally, rinse with water and dry.

4. Simple Green

SIMPLE GREEN ndustrial Cleaner and Degreaser, 1 US GALLONAnother option for sealed concrete block walls, Simple Green can tackle mold directly and inhibit future growth. As a commercial cleaner that comes in several varieties, you’ll want to follow the manufacturer’s instructions regarding application.

Usually, the simplest option is a spray-on version. With that, you can saturate the mold, scrub the spot with your brush, and finish with a water rinse and towel dry. If you opt for another product, you may need to dilute the Simple Green first, based on the manufacturer’s directions.

5. Zep

No products found.Another commercial cleaner, No products found. is a bleach-based product designed to conquer stains without scrubbing. However, if you’re actively dealing with mold, a bit of elbow grease might be necessary.

If you get the version that’s already in a spray bottle, simply apply based on the manufacturer’s directions and use a scrub brush to tackle tough spots. Then, quickly rinse before drying the wall.

If you go with a non-spray bottle option, it may be best to pour some into a spray bottle. Usually, that gives you more control, and since Zep can be harmful to certain materials, that’s often ideal.

6. Pressure Washer

Sun Joe SPX3000 Electric Pressure Washer, 2030 PSI | 1.2 GPM Rated Flow | Dual Detergent Tanks | Ideal for Cars/Fences/RVs/ATVs/Patios/SidewalkFor mold on an outdoor concrete block wall – or in basements with good drains on the floors – using a pressure washer is an option. You’ll want to start slowly, increasing the pressure until you see it removing the mold. That way, you limit your odds of damaging the concrete blocks.

Once you reach that point, work slowly, using even and controlled motions to tackle the mold. Then, make sure to push the water toward a drain or away from your home once you’re done.

With some pressure washers, you can add cleaners to the mix. Just be aware that not all cleansers (including some options above) are suitable. Follow the manufacturer’s directions regarding adding cleaners, and only use products that are explicitly listed as options.

How to Clean Mold Off Cinder Block Walls

Technically, any of the options above can clean mold off cinder block walls. If you aren’t sure where to start, consider beginning with either hydrogen peroxide or vinegar. Both of those aren’t usually irritants to people. Additionally, they aren’t harmful to clothing.

However, you can also try a mixture of liquid dish soap and water, if you prefer. Simply mix a few generous squirts into a bucket of warm water. Then, use a scrub brush to apply the mixture and clean the area. Once you’re done scrubbing, rinse the walls with warm water. Finally, dry them with a towel.

For stubborn mold on sealed concrete, you may want to try bleach. It’s highly effective, though harder to work with than the other options above. The same can be true of Zep.

Can You Paint Over Mold on Concrete?

While you technically could paint over mold on concrete, it’s not something a person should do. Even if the paint is designed to inhibit mold, most are meant for clean, dry surfaces. If there’s mold, there’s like dust and debris and a potential moisture issue.

Additionally, if you don’t remove the mold first, the paint won’t adhere properly, leading to chipping and peeling down the line. The mold can also grow through the paint. Then, you have the same mold problem on the freshly painted surface.

Plus, the mold can continue spreading underneath the layer of paint, as the underlying surface may still be damp, and food sources could be available. In some cases, the impacted area may expand significantly without outward signs that it is occurring, causing the problem to get much bigger before it’s detected.

As you paint, you’re essentially spreading the mold spores with each brush stroke or roller pass. That can potentially make the problem worse, as you’re dragging the mold to new areas where it might flourish.

That’s why it’s essential to completely remove all mold before you paint the concrete. Once it’s cleaned up, let the concrete dry completely to improve adhesion and reduce the odds of mold-growing trapped moisture.

Then, if you want to limit future mold growth, choose a paint designed to prevent or inhibit mold and mildew. That way, you have some extra help in the battle against mold.

Should You Call a Professional?

Whether you should call a professional mainly depends on the size of the issue, the molds involved, and your health (or the health of household members).

Those with breathing issues, lung conditions, or allergies may be better off contacting a professional if there is a notable amount of mold, regardless of the type. That way, they can limit their exposure while ensuring the problem is handled correctly the first time.

Similarly, if a large mold problem spans more than a couple of square feet, contacting a professional could be wise. Along with addressing the mold, they may be able to identify the source of the problem. Plus, with an issue of that size, your odds of having mold in areas you aren’t noticing may be higher, and they can help determine if there’s another mold you need to handle.

Finally, if the spot is bigger and the mold is either black or dark green, you may want a professional to come in and test the mold to determine its type. In those cases, there’s a chance the mold is toxic, making it potentially harmful to anyone. By getting the test, you’ll know if this is an issue you can handle yourself or if you’ll need a pro to ensure it’s done right.

How to Prevent Mold on Cinder Block Walls?

If you want to prevent mold on cinder block walls, cleanliness is often the key. By washing the concrete block walls with a liquid dish soap and warm water mixture, you can remove dust and particles that would serve as a food source for mold. As a result, it won’t have the nutrients it needs to grow.

Otherwise, you can use a mold-inhibiting sealant or paint to prevent mold growth. With this, your first step is to thoroughly clean the cinder blocks, ensuring proper adhesion. The dish soap option above can work well, though you can also go with hydrogen peroxide or vinegar.

After cleaning the walls, make sure they dry completely. Then, apply the sealant or paint following the manufacturer’s directions.

If your cinder block walls are in a high-humidity space, such as a damp basement, you may want to bring a dehumidifier during the painting or sealing process. Have it running while you clean the walls, and leave it going until you finish sealing or painting and the coating is dry.

In some cases, keeping the dehumidifier going long term may also be wise if dampness is an ongoing problem. Just make sure to read the manufacturer’s directions regarding use, including how to clean and empty the machine. That way, it can work correctly without becoming a new potential source of mold or mildew.


At this point, you likely have a pretty good idea of how to get rid of mold on concrete block walls. If the wall isn’t sealed and you prefer a natural approach, hydrogen peroxide and vinegar are solid choices. For sealed concrete, bleach is a good choice. Plus, you can always go with commercial cleaners, if you prefer, potentially simplifying the process.

Did you learn everything you wanted to find out about how to get rid of mold on concrete block walls? If so, let us know in the comments. Also, if you know anyone who could benefit from this information, please share the article.

Written By: Yevgen

YevgenI'm a DIY nut, and the founder and chief editor here at Weekend Builds.
This site is a result of my DIY passion, and to share the joys I have experienced fixing, building, and creating things over the years.

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