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
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....
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.
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.
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
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.
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.
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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