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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?

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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

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