Removing dark staining on our concrete patio

August 5, 2024 2:18 PM

What can I do to remove dark areas on our concrete patio?

Here are a couple of photos.

The dark areas have come off with pressure washing in the past, but came back full force within a year. It looks like it might be the same thing that's on our concrete driveway as well.

Any ideas?

posted by cozenedindigo to Home & Garden (6 answers total)

We had dark stains on our patio due to curing issues. My kid spilled lemonade on it during an evening party and it sat overnight. When we washed it away, the dark area had faded and never came back. I then treated the rest of the dark spots with some diluted vinegar, which also worked! This was years ago now and we've had no further problems. I'm not sure what's causing your recurring issues, but it might be worth testing a small area with a weak acid.
posted by pizzazz at 3:06 PM on August 5

It's most likely mold. Is the area frequently wet, or in the shade?

There are sealants you can apply to clean concrete to prevent the buildup from coming back.
posted by JoeZydeco at 3:18 PM on August 5

At one of my workplaces we used Wet and Forget for staining like this. It does need to be reapplied (probably annually, depends on the weather and what kind of sunlight the area gets) but it doesn’t need a power washer, you can apply it with a gallon-sized pump-handle hand-held sprayer.
posted by bcwinters at 3:18 PM on August 5

I would guess it's mildew on a part that never gets totally dry. Does the shape match an area that's always shaded?
posted by nouvelle-personne at 4:17 PM on August 5

Response by poster: I would guess it's mildew on a part that never gets totally dry. Does the shape match an area that's always shaded?

Actually the opposite. The dark part is in full sun and the part that's not stained is covered by an overhang.
posted by cozenedindigo at 4:46 PM on August 5

Muriatic acid, then Wet&Forget
posted by at at 6:26 AM on August 6