Cleaning Mold On Basement Walls

Basements are usually dark areas, with poor ventilation, and tend to have higher than normal humidity. Under these favorable living conditions, mold will grow rapidly and thrive. Mold can come in a variety of colors, from black to white, and from blue to green. Mold’s color and type are not too important. What is important is getting rid of it. Successful cleaning of mold on basement walls can be difficult unless the causes allowing for mold growth are first addressed. Foundation leaks, caused by years of wear and cracks in walls and floors, along with condensation on plumbing and HVAC pipes and vents, tend to help maintain humidity levels that are higher than those normally found in above ground areas of the home. Another reason that cleaning mold on basement walls is difficult is due to the porous, rough surface of concrete. It’s hard to reach deep into all the tiny crevices and pores.

When you see mold on basement walls, the mold is not growing on the concrete or the concrete blocks. Mold cannot “eat” concrete because concrete is not an organic substance. Organics, along with moisture, are some of mold’s requirements to grow to survive. Usually the mold is growing on dirt and dust or paint and wall coverings that contain organic components. Many paints are latex-based and latex is an organic compound.

Note: This article discusses how to remove mold on concrete walls. If you have mold on other surfaces like sheetrock or wood, read our mold removal guide.

Basement wall with mold

Steps to Clean Mold On Basement Walls

When it comes to cleaning mold on basement walls, scrubbing with detergent and water is the first step. Vacuum or sweep down the walls to remove as much dry material as possible. After that, washing down the walls with soap and water will help remove most of the remaining dust and dirt that has accumulated. Many so-called “experts” will tell you that a bleach and water solution (one part bleach to 3 or 4 parts water) will work. The thing is, we want to remove the mold, not just kill it. Remember, extreme caution must be taken when using chlorine bleach in an enclosed, poorly ventilated area. The fumes from bleach can easily overwhelm if you don’t take the proper measures to protect yourself. Opening windows and wearing a respirator is highly recommended.

Because of the chemical nature of bleach, it is hard to work it into the concrete’s pores. In addition, bleach manufacturers only recommend using bleach on non-porous surfaces. Rub your hand over a concrete wall. It is definitely porous. Also bleach can be corrosive and can cause further damage. Yet another reason to avoid using chlorine bleach is that when bleach comes into contact with organic materials, the organics tend to render the disinfectant qualities of the bleach ineffective. Bleach always works best on clean, non-porous surfaces.

A better way to clean mold on basement walls is to use a one-to-one solution of white vinegar and water. Vinegar will kill 82% of mold species. The vinegar will not only penetrate the concrete better, it will also act as a disinfectant. Scrub the vinegar solution into the concrete using a scrub brush with stiff bristles. Since vinegar is mildly acidic you should always rinse any areas you applied it to with water and allow the area to dry.

You can also use hydrogen peroxide to remove mold. You need to use it full strength and you need the hydrogen peroxide to have at least a 6% concentration. You can find higher 6% concentrations of hydrogen peroxide at most beauty supply stores for around $20-$30 a quart. Put it into a spray bottle, thoroughly saturate the area, and allow it to dwell for a minimum of 10 minutes. After that, rinse the area with water and wipe it dry. Always use caution when using hydrogen peroxides with concentration contents above 3% as it may cause chemical burns on your skin.

Yet another method to remove mold from concrete is to use a pressure washer. If the basement is empty of all furnishings and personal items, a pressure washer can be highly effective to clean mold on basement walls. Be sure to leave the pressure washer outside the house to avoid filling the basement with carbon monoxide while you work. Of course this method also requires you to wear the proper protective equipment - gloves, a mask or better yet, a respirator, and waterproof clothing. Spray a detergent solution onto the walls and allow it to dwell on the walls for 10-15 minutes. Then scrub the treated areas with a stiff bristle brush before using the pressure washer to remove the solution. When using this method you must have a way to completely remove all of the remaining water and then dry the entire basement thoroughly.

Preventing a Reoccurrence of Mold

As important as it is to clean mold on basement walls, it is equally important to take steps to keep the mold from returning. As mentioned, most mold problems in basements are due to a lack of ventilation and the presence of high humidity. You can alleviate the humidity in your basement by using a dehumidifier. These units can be found for under $300. I recommend a model that will self-empty, having pump-out capability or by continuously draining through a garden hose that can be directed down a drain. Here is more on selecting the right dehumidifier.

Another preventative step you can take is to primer/paint the concrete walls with a mold resistant product after the removal process. An excellent choice is Zinsser Primer on Amazon. These mold resistant products will range in price from $30-$50 per gallon. Most of these mold resistant primers and paints contain antimicrobial ingredients that help prevent mold re-growth in areas of high moisture content. Warning – I never recommend attempting to cover, seal, or paint over mold in any situation.

The goal is not to kill the mold (you won’t kill the mold spores by scrubbing and washing) but to completely remove it.

Consider the following example: If you have a skunk living under your front porch, you have a problem. If you kill the skunk you haven’t solved your problem, you have just created a different problem. Now you have a dead skunk under your porch. The same goes for mold. Don’t be happy with just killing it… it needs to be removed.

Help Is Just One Click Away

After reading about cleaning mold on basement walls, you may have decided that professional assistance may be the smart way to proceed. We have a list of mold removal experts in your area that will provide a free in-home inspection and evaluation to solve any mold issues you may encounter.

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Written by Mark Huey.