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I set a bag of grass clippings on my driveway, and then forgot about them on garbage day. When I remembered to put them out this week, the bag left behind a black goo on the driveway. I tried scrubbing it with water and a scrub brush, and even tried some Clorox clean up. But the stain is persistent.
What is the best way to clean this type of stain off of concrete?
As the grass decompose, it releases tannin, a colorful byproduct of the natural decaying process. While the color will eventually fade from concrete, you can help hurry the process along with a little bit of driveway cleaning.
Spray the stained area with a garden hose to rinse away dirt. In a large plastic bucket, mix ½ cup of liquid dish detergent into 3 gallons of hot water. (Or, for the best results on tannin stains, use a powdered laundry detergent that’s advertised as being good at removing food stains.) Slowly pour the solution onto the tannin stains and work the liquid into the concrete using a stiff-bristle nylon brush. Rinse with the garden hose and, while the concrete is still wet, sprinkle powdered laundry detergent over the stains and scrub again. Leave the detergent on for a few minutes then rinse away. Repeat if necessary
