How can you get mildew of concrete?


I think we all have green mildew on some part of our concrete, does anyone know how to get it off and how to prevent it from coming back? I've tried scrubbing it with some soap and not all of it comes off. TUIA.

  7 answers
  • Seth Seth on Oct 29, 2018


    Is this inside or outside? Mold does not grow on concrete. More likely it is algae, lichen, or moss if outside. Scrape as much off as possible with a putty knife or paint scraper. Spray it with a bleach and water solution. Let it soak in for a long time before washing off. You may need to do this more than once. Protect any plants that are close by. You may need a stiff bristle brush to remove all of it. As a last resort, you can use muriatic acid. Anything you do will most likely change the color of the concrete slightly and might be noticeable. it will continue to grow where conditions are favorable, usually areas of a foundation that care not in direct sun and stay wet. You need to stay ahead of it by cleaning a few times a year.

  • Brenda Coburn Bull Brenda Coburn Bull on Oct 29, 2018

    You can either pressure wash it or use full strength Clorox with a stiff bristle long handle brush. Make sure you don't get any on you or your plants. Unfortunately there is nothing that I know of to keep it from coming back eventually.

  • Ebbjdl Ebbjdl on Oct 29, 2018

    Straight bleach, this concrete must be on the north side of the house, The sun is scarce in the winter. Aloha!

  • Kelli L. Milligan Kelli L. Milligan on Oct 29, 2018

    That may be algae or a moss? Is it in a shady spot? Have you tried power washing, pour some bleach on it. That kills about everything.

  • Ara Ara on Oct 29, 2018

    Thank you all very much!! My bad it is Algae. I knew about the bleach, I was just wondering if there was anything else other than bleach. I very much appreciate your responses!!

  • Vinegar is my go to. Be generous, at $2 a gallon it is far less expensive than any chemical cleaner. Pour it on, let it sit, then brush brush brush, then hose off.

  • Kathy Gunter Law Kathy Gunter Law on Oct 29, 2018

    Wet & Forget Outdoor is a good product that will clean as well as prohibit. It's a no scrub solution that will work over time. If you can't wait, scrub with vinegar to get it down to a smaller issue then start using wet & forget to keep the issue at bay. We had a horrible problem on our front porch stairs and they were green & slick. This fixed it for us and it's been a few months. Area gets almost zero sun but lots of rain & water.