How To Clean Up Black Mold On Walls

Doug asked: How do I clean mold on cement block wall and cement floor? One end of my shop is built into the side of a hill. I am in Minnesota, so the inside wall below grade is usually cold, or cool, and damp. Mold forms on the lowest two feet of the back wall, as well as the cement floor in the back corners. The walls and floor are painted. What is the best way to remove the mold? I want to clean it up so it can be repainted.

Moisture can move through underground cement in many ways. Often there are moisture barriers in place, but they can wear out and become less effective over time. The porosity of cement blocks make it a key area for mold growth. The moisture is able to get it, but has no way of drying up, which makes the perfect landing spot for mold spores to prosper. No matter how the moisture got there to begin with, it's important to remove the mold completely. Be prepared to put some work into it. The materials are easy – but it's going to take plenty of elbow grease to get rid of the mold completely.

You Will Need:

Long sleeves and pants
Goggles
Mask
Water
Bleach
Bucket
Scrub brush or sponge
Rubber gloves

Steps to Remove the Mold:

Mold is a toxic substance. Protect yourself by wearing long sleeves and pants, goggles, and a breathing mask. You can rent a respriator from a hardware store if needed. There are also hooded coveralls that can be found at hardware stores or online.
Bleach is a well-known killer of mold and bacteria. In this case, it's the perfect cleaning agent to kill and remove the mold completely.
Start by mixing 1 part bleach with 4 parts water in the bucket.
Put on rubber gloves to protect your hands and wear old clothing as they will likely get a splash or two of bleach on them. If you can wear clothes you wouldn't mind throwing in the trash when you're done, that would be ideal.
Use a scrub brush or sponge, depending the surface and severity of the mold, and dip it in the bleach solution.
Scrub the mold with the solution until it is gone.
When all of the mold is removed, dry the area completely by patting the surface with towels to remove excess moisture, then pointing a fan on the area if needed.
Consider sealing the concrete with a mold repellent to prevent its return. These products can be found at hardware stores. Moldex is one popular example.

Additional Tips and Ideas

Protect yourself when using bleach. Always wear protective rubber gloves and open any doors or windows to allow for proper ventilation.
If you are planning to paint the area, consider applying a sealant to the area to prevent moisture from coming through again.
There are commercial mold removers available at most hardware and home improvement stores. They are specifically designed to remove mold from concrete walls and floors.

Sources

How to Clean Practically Anything by Consumer Reports
Cleaning Plain & Simple by Donna Smallin

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