Cleaning concrete driveway?

Typical concrete driveway and porch that is gotten dark and dirty over time. Can I just use a pressure washer to clean? I hear that whatever causes the dark stuff will come back if done this way and maybe there's some special cleaner?
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Grendel wrote:

very microscopic holes on the concrete fill up with mold... it does not wash away with a hose as its in the tiny holes and stays there... a pressure washer will lift it out.. and nature will take its course and let it start growing again.... no mater what you use its gonna come back.. i had a container of pool chemical that had hardened in the plastic container. and being as it was clorine( just concentrated bleech) i beat it with a hammer and it went back into a powder and i wet the sidewalk with it and then sprinkled it onto the wet sidewalk like a paste and scrubed the sidewalk and let it sit there in its wet state... it killed the mold in the tiny holes and the sidewalk looked real clean(it also made the grass close to the sidewalk yellow/brown as it kills grass also)... looked good for a couple of months but then back to black..... for a check on it you can use some bleech and see it it helps any, but remember that one gallon of bleech is about as powerful as one ounce of this clorine for the pool....
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Grendel wrote:

Usually that stuff is mold/moss. The pressure washer will take it off, but as noted, older concrete is a better host and it will come back. Where I am I pressure wash it about twice a year. That takes care of it for me.
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A good pressure washer will produce amazing, almost addictive, results. You'll also notice much greater traction with the mold gone.
Eventually it'll darken up again, but it usually takes a long time.
Grendel wrote:

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Thanks guys.

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snipped-for-privacy@grendel.com says...

Grendel-
Here's what I did:
Step 1. Bought a whole bunch of regular grocery store chlorine bleach in the big bottles.
Step 2. Poured batches of the bleach onto the concrete.
Step 3. Used a bit nylon-bristle pushbroom to spread the bleach, full strength, over the concrete. Repeat on a new area with a fresh batch of bleach.
Step 4. About half an hour later, rinsed thoroughly with water.
It helps to do it on a sunny day, because the sunlight helps activate the chlorine. It also helps if the day is a bit breezy because the breeze disperses the chlorine smell. Chlorine from bleach can be irritating (I like the smell, actually).
Extremely effective, very low effort, very low cost, and a year later the concrete still looks good. It will darken again, but so far so good.
Marc
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Swimming pool bleach is sometimes suggested when household bleach doesn't get it done. Probably need less for same results.
wrote:

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wrote:

Pressure washing is the proper way to clean concrete. I've never cleaned my concrete driveway, other than sweeping it after trimming the lawn. It still looks clean after 14 years. Perhaps some TSP or detergent soap will clean it, but not knowing the cause of the "dark" this may not help.
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Get a box of Tide w/bleach laundry soap. Broadcast it over the driveway. Afetr a few rainshowers the driveway will look like new.

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Go to the pool store and buy a bottle of chlorine. It's stronger than Clorox. I use that - it takes off a lot of stuff but it won't help oil or rust (found in some water). It will take off mildew and dirt. I tried pressure washing - it wasn't a commercial type - so maybe it wasn't strong enough, but the chlorine did a better job...with garden hose for rinsing.
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