How to Remove Mold from Cement Walls and Floors

moldyconcrete

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:

Steps to Remove the Mold:

  1. 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.
  2. Start by mixing 1 part bleach with 4 parts water in the bucket.
  3. 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.
  4. Use a scrub brush or sponge, depending the surface and severity of the mold, and dip it in the bleach solution.
  5. Scrub the mold with the solution until it is gone.
  6. When all of the mold is removed, dry the area completely.

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.

Comments

  1. Maueen says:

    Very good article on cleaning up mold from cement. However, I would add that the person cleaning should also wear a respirator (just something simple from the hardware store) – you don’t want to be breathing the mold spores.

    Additionally, if your mold is in the basement and you can see it, I would not run HVAC until it is cleaned up. It may spread the spores throughout the house.

  2. Eric says:

    I use full strength bleach in a spray bottle. Just soak the cement wall with the bleach, let it stay for an hour, then wash it clean.

  3. LO says:

    This is not a mold question. We have the mold removed and painted the cement floor. Unfortunately, white paint got on the sand color paint; we removed it and we now have black steel marks on the cement and paint. We need to be able to remove those. We have used Spic and Span, also a Mr. Clean Eraser. Neither have hardly touched the black left behind. We need to get this repainted with the sealant paint, but need the black gone first. Any suggestions?

  4. Linda says:

    I would appreciate any suggestions that anyone has on how to remove steel black scratch marks on a concrete garage floor, since we have moved some appliances.

    If you have any procedure that will remove these marks, please send me whatever works the best. I am trying to get the garage cleaned up, and am having trouble removing the steel black scratch marks left by moving heavy side-by-side refrigerator, and large freezer.

    Thanking you in advance,
    Linda

  5. Christine says:

    I have one addition to Maureen’s suggestion to use a respirator. I strongly urge anyone contemplating working around mold to wear safety goggles. I cleaned a dehumidifier outdoors, and now have fungal keratitis in my left eye. Keratitis is painful and threatening my vision in that eye. Bleach droplets from a scrub brush could be harmful, too. If you develop a red, itchy eye after working on black mold, just immediately get yourself to an ophthalmologist (not optometrist). Or save yourself a lot of pain and trouble and wear wrap-around goggles.

  6. Mike says:

    Thanks for your suggestion, Christine. I plan to do some scrubbing and will seek out some eye protection.

  7. Ed says:

    Can mold grow inside concrete slabs via cracks where there is water intrusion and there are steel and steel cables within the concrete?
    Can mold grow inside concrete walls after years of water intrusion?

  8. Melanie says:

    Ed, if moisture and air are present, mold can grow. Also, moisture and air can travel through the concrete, carrying with them mold spores. However, it is unlikely that mold would grow on the inside of a slab of concrete because the air flow is so low. In cracks, however, air flow would be greater.

    Source: University of Illinois
    Source: Iowa State University

  9. Dave says:

    You can’t clean mold off of cement. Cement is actually a microparticle that is the binder in concrete and concrete block.

    Calling concrete “cement” is the same as calling bread “flour.” It is only one ingredient in the mix.

  10. Greg says:

    Hi, we have a white furry mold on a ground floor concrete block wall. We have washed the areas with bleach a number of times, but the mold returns. The block feels damp on the inside, but I have drilled holes from the outside thinking maybe there’s water, but each cavity is dry. I do wonder if our daughter’s cat may have sprayed and the mold is the effect. We are now going to try a number of different cleaners on the different spots. Any other ideas appreciated. Just a note that the outside wall is a sun trap.

  11. Bo says:

    Ok, the wall has been cleaned of mold; then what do you do?? Paint, or more mortar???

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