How to get rid of mold on basement walls? There are six steps that I’m going to highlight below. First, be sure to watch my video on this topic and subscribe to my YouTube channel for more tips and resources.
Step 1: Diagnose the Cause
The number one step is to diagnose why you have mold on basement walls in the first place! We can jump into cleaning the mold on the basement walls, but if we don’t figure out why the mold is there, then with no changes to conditions, the mold will usually come right back. I don’t recommend cleaning the mold until you’ve figured out why it’s there, corrected the ‘why’, and dried out the space.
So diagnose the cause first. The cause is usually coming from some drainage defect outside. In my Build a Safe Home course, I teach an entire module on site drainage. Check that course out for a really fast track to the details you need to focus on in building or even restoration projects.
When water is apparent in a basement, it is time to get outside and start walking the structure and looking closely. Any water paths that you can’t see, like downspouts that are going in the ground, are suspicious because you can’t see where the water is going or if water is flowing well. Sometimes clogs below grade will lead to downspouts overflowing at the connection pipe to the ground.
My second tip on diagnosing the cause of mold in basements is get outside WHILE it’s actually raining or immediately after it stops raining. Look for puddles. Look for dark spots on your walls. Look for anomalies – something that doesn’t look right or look like adjacent surfaces of the same material. Also, look for places where wood chips have gotten moved because of a flow of water or puddles. Those areas of displaced wood chips, can be a sign to tell you where the path of water is going and settling.
A lot of our buildings today are built on very flat ground that does not drain away from the foundations. Whether the foundation is concrete block or concrete poured, both are porous and absorb water like a giant sponge. The foundation is going to draw the moisture inside and that moisture will always dry to the inside. If it gets trapped or if it can’t dry fast enough, then the mold is going to grow on basically dirt and dust. You definitely want to diagnose the cause and figure out where the moisture is coming from and eliminate that moisture.
Step 2: Stop the Cause
Number two is stopping the cause. Once we’ve diagnosed the causes, the next step is to stop it. The solution could be something like pulling the downspouts out of the in-ground connection and redirect them to go over-ground, so that the path of the water is readily apparent and definitely moving away. This change may require a change in grade slope adjacent to the foundation. Sometimes directing the downspout water to a French drain at least 10 feet or more away from the structure is helpful. A French drain is a shallow drain that is sloped to daylight somewhere nearby but NOT next to the structure. French drains carry water further away as part of a culvert or hidden under grass. They will allow the creation of a concealed hill to carry water away via a pipe and gravel.
Always also look up when checking your home. Clogged gutters that overflowing are often a cause of moisture accumulation in basements. Any location where valleys come together, where two roof lines meet, can also overflow the gutter due to the volume of water collected in these areas. This will dump large quantities of water into the interior corner soil and contribute to the area getting more and more depressed, collecting even more water over time. That water soaks into the ground and soaks into the foundation and ends up in our homes.
Step 3: Dry It Out
Number three is to dry out the area… both the soil adjacent to the home AND the basement, crawl space, or slab itself. A dehumidifier can be helpful, but even moving air with a fan can facilitate drying. Be cautious of using fans if mold is apparent or expected, as fans can blow mold around as well. For the soil, cut back plantings so that the sun and wind will help dry out areas.
If an actual flood has occurred, it may be necessary to use a ShopVac or a pump to get the water out. Consider calling your insurance company as flooding may require special procedures and equipment. Dehumidification, towel drying, moving air, opening windows, ventilation, all those things will help with drying. Monitor the humidity levels so that you can ensure movement towards dryer conditions. Dehumidifiers need to be an enclosed space because they can’t dehumidify the whole world. They must be able to achieve the humidity goal/setting that you select. Windows and doors should be closed if you’re going to use a dehumidifier.
The goal is to bring the humidity to 40% or lower and get it to stay there, allowing the dehumidifier to turn off. Do this in a basement or crawl space or even in a home on a slab. When it rains again, humidity might return, if so go, back to more review for causes.
Step 4: Clean
Next is cleaning. In some cases this can be started while drying is ongoing – especially if mold is apparent, suspected, or if spaces are very dirty or dusty. I recommend using non-toxic cleaners. According to the EPA, mild detergent will work to wash away mold, including the dirt and dust mold is living on. Removing dirt and dust will go a long way toward removing mold. So clean, clean, clean! I prefer essential oil based cleaners as recommended by Dr. Edward Close, PHD through his research. He recommends Thieves Cleaner which can be purchased here: www.essenty.com/dwellwell. Use my sponsorship #3243004 to qualify for my free support community related to essential oil products.
Never use bleach. I have another blog post about this here. Bleach is very toxic. Also I do not recommend using ammonia or mixing any of these with other products. You can search online for “PubMed antifungal essential oils” to find articles about the effectiveness of various essential oils in the context of mold/fungi or even bacteria.
Using baking soda, lemon juice, and/or vinegar are also great cleaning options. The goal is to clean and get rid of the dirt and dust. Never use a hose or inundate a home with water. Damp wiping and HEPA vacuuming are easy to do.
Always take precautions to protect any occupants, or workers. Paper masks are NOT enough! Anyone who is cleaning should be protected with a quality respirator, Tyvek suit to protect clothing, goggles and gloves. The mold cleaning process can be very, very toxic and dangerous!
Step 5: Dry Again
Number five is dry again. Most likely you’ve used some water in your cleaning process. This water must be removed. Again, you want to use as little as possible, which is why I like plant-based products – because you can use those with very little water. Always dry and then dry again. Make sure that humidity is down within normal limits (40-45%) and that the dehumidifier does not need to run constantly to maintain this. You can alternate between opening windows and ventilating and dehumidifying. Be cautious of introducing very humid air from outside if you are in a hot and humid climate.
Step 6: Observe
Number six is observe. Make sure that all you have done has worked. Do not replace finishes! In fact, I don’t recommend reintroducing them in a basement until it has been confirmed that corrections to keep the area dry have succeeded. That can take up to a year or more. Most people can use their unfinished basement. It is only the exterior walls, in most cases, that are compromised. Never put cardboard boxes or store lots of paper in lower levels or against concrete. Keep even plastic bins up off the floor to allow for air flow and constant drying.
If you find that there’s still water evidence over time, repeat the cause discovery process. Getting mold under control and cleaned from lower levels can be a long process with lots to learn by trial and error as you discover the defects in your home and learn how moisture is moving through your structure. The protocol for diffusing full strength essential oils developed by Dr. Edward Close can also be helpful to keep mold spores at bay and keep them from returning along with the other steps I have shared.
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Cheryl Ciecko, AIA, ALA, LEED AP, is a licensed architect who helps homeowners and building professionals create safe homes through online education to prevent mold, water damage, and poor indoor air quality.
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The information contained in this presentation is for educational purposes only and is not intended to diagnose, prescribe, treat, or cure any disease, ailment or injury to the body. It is not medical advice. FDA regulations prohibit the use of medical claims in conjunction with the sale of any product not approved by the FDA. Statements made herein have not been evaluated by the FDA.
Any products, techniques, and/or personal usage tips referred to are not suggested as a replacement for proper treatment from a licensed health care professional. I am not a licensed health care professional and the decision to use or not to use any of this information is the sole responsibility of the listener and/or reader. Everyone is an individual with different body types, different blood types, different body chemistries, and it is important to remember that what works for one person may not work for another person.