I don't know what you would use to clean it, I have never had that problem if I did I would be sure there were no bushes or shrubs shading the patio to much. Usually damp dark places cause mold and moss. I have seen mold behind bushes on houses.

There is nothing overhanging the patios, they are just 30 years old and never cleaned by the previous owner. I'm glad to hear you haven't had mildew on your concrete. We get a rainy season here, so the concrete stays pretty wet for a couple months. It's a very common problem for unsealed concrete to get black with mildew, thus all the articles online with all their conflicting advice! I plan to seal it after cleaning all the stains off, but would like some advice from those who have had this issue to deal with before deciding how to spend my weekend (and whether to spend the money on renting a PW).

My experience with a PW on decks was to keep it moving, don't ever leave it running in the same spot, it will dig a hole. We had some mold on one of our decks that we built around a low growing tree and power washing worked on it. I would think concrete would be harder to damage than that. If you have a lot of dampness in your area ask one of your neighbor's or a home improvement store in your area.

Good Luck.

You either scrub manually or use a powerwasher.

If you find the right scrub brush, not too stiff, not too soft, and put it on a long pole (so you don't have to bend over), you can work on the patios over time and get it done. IMO, power washing never seems to get things really clean.

power wash,there is a product at Lowes works great but hubby killed a few of my shrubs with it,just for grime.mold

Power wash it but go in a back and forth motion from the flower beds outward. Don't leave the spray on one place too long. You can always go back and redo missed spots.

Out patio was built about 25 years ago with colored slabs and we have power washed it 3 times so far and it will get a going over again this spring. The only thing it did was remove a little color--a very little color and they look great after they are done. The power washer removed the mold and grime. Our patio is in full sun so mold will eventually grow on slabs no matter where they are.

I tried a brush and cleaner a few years before we got our power washer but never got the results we got with our power washer

The power washer definitely did the job! Our neighbor actually owns one and offered it when I mentioned I planned to rent one - so I cleaned our shared carport as well. 30 years worth of algae/mildew/stains took hours of cleaning to remove but the concrete looks so much better now.

Last year when we bought th place I tried scrubbing with a stiff bristle brush on a broomstick with various cleaning agents and barely removed anything. With the power-washer I got everything off.

Clear line between the clean walkway and the dirty during washing!

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Patio after power-washing.
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