How do I keep a concrete patio clean?

How do I keep my concrete patio from being green moldy and black and dirty? I’ve tried using a power washer and it just comes back dirty in a few months 😕

  7 answers
  • Seth Seth on Jun 01, 2019


    We have the same problem. Our walk out basement concrete patio is in the shade most of the time and stays wet. We just try to stay ahead of it by cleaning frequently. Don't wait until it looks bad. Unless you eliminate the conditions causing the problem, it will keep re-occurring.

  • Betty Albright-Bistrow Betty Albright-Bistrow on Jun 01, 2019

    Hello Jill!

    Truly it is something you want to keep after. I have the same problem and I am going to try a couple of things to clean our patio up. It gets stained from weather, stains from dirt, etc.

    1: Semi-Dirty Outdoor Concrete Cleaner

      BleachWater1/8 cup dishwashing detergent

    Mix bleach with water and then add dishwashing detergent to the mix and put it into a spray bottle. Spray the solution onto the cement patio, let it sit for a few minutes, then scrub the mix into the concrete with a stiff brush.

    2: You'll need 2 parts baking soda and 1 part bleach. I usually start with two cups of baking soda and one cup of bleach. But, that is a fairly small amount. Feel free to double or triple (or even quadruple) this recipe since most patios are large sizes.

    The patio cleaner will be thick and soupy (is that a contradiction? Like pea soup, no?). Grab some rubber gloves and a large scrub brush. I made my paste in a shallow glass pie plate (I wasn't sure how bleach & baking soda would react with metal, so I opted for glass to be safe). I would just dip my brush and scrub the concrete. Then rinsed it all when I was done. I did line my patio with old sheets to catch the runoff. I didn't want to harm my grass or let too many chemicals just go into the big, wide world.

    3: Remove furniture and all other objects from the patio, especially planters. Dirt often wedges underneath planters.

    Sweep the patio thoroughly, working side to side and then going over the area again in the perpendicular direction. Work in small sections and apply a vigorous hand to remove as much dirt as you can.

    Rinse the patio with a hose or a pressure washer. While the patio is still wet, squirt some liquid dish soap directly onto the surface.

    Scrub the patio with the broom, working the suds into the concrete. Rinse the patio again with the hose -- and use strong water pressure -- or a pressure washer.

    Remove stubborn stains from the patio by pouring a small amount of bleach onto the concrete. For better control over how much comes out of the bottle, pour some bleach into a plastic spray bottle and spray the concrete instead. Alternatively, mix 2 cups of vinegar and 1/2 cup of baking soda in a bucket of warm water and apply this solution to the concrete.

    Scrub the solution into the concrete with a bristle brush. Let the solution sit for about 15 minutes. Rinse it away with a hose or pressure washer.

  • Michelle Baumeister Michelle Baumeister on Jun 02, 2019

    You sound like my hubby (I personally like that natural look). Get a power washer. Makes him happy until the trees drop their latest.

  • Liz W Liz W on Jun 04, 2019

    Try painting it! If it’s colored, even though you know it’s there,you won’t see the moldy spots.

  • Ginger Ginger on Jun 04, 2019

  • Oliva Oliva on Jun 04, 2019

    After washing, dry thoroughly then liberally apply Wet n'Forget using a garden sprayer, applying on a day when no rain is expected.

    • Jill Keating Raburn Jill Keating Raburn on Jun 04, 2019

      I tried that last year. Didn’t seem to last more than a few months. I was hoping for better. Have you had luck with it?

  • Oliva Oliva on Jun 07, 2019

    Hi, Jill,

    The washing won't last unless you've completely removed all the algae, which is very time consuming on a textured surface. The trick is to over saturate the surface with Wet n' Forget, to the point of run off. You'll need to protect plants and grass. The Wet n' Forget may need reapplication after 4-5 months, but is does work, although it's very slow.

    If your concrete receives little sun, the algae growth can be worse. In that case, you can apply a 10: 1 mix of water and chlorine bleach, scrubbing with a shop broom. Do not rinse. You should see an improvement in 48 hours.

    Note that having a water feature nearby (exposed to sun), overhanging trees, or nearby mulched areas can further add to the algae problem.