How to clean a concrete walkway

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The 4' wide concrete walkway to my front door has become stained and unsightly. Part algae, part burn marks from burning palm seeds dropping on it, part just a discoloration of unknown origin.
If I use Clorox bleach on the concrete, that would be as starting point to clean it up. My question is, will chlorine harm the concrete?
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Walter
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wrote:

No. You also, won't get the burn marks out, sorry.
Remember to not track bleach back into the house and the new carpet.
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Oren wrote:

Dang, you just killed a (possible) new thread :)
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dadiOH
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What will it take to get the burn marks out? Sandblasting??
Thanks
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wrote:

We don't know how deep and severe they are. It will etch the surface like the pressure washer. There are various blast media that are less abrasive. A local could help with the answer.
Perhaps an acid etch and stain would be the less costly approach.
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A Clorox solution may help but is not effective on all stains. It is most effective on mold and mildew stains. The best solution will be a high-pressure wash with pre-treatment using the bleach.
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I agree with Bob. The bleach can kill it, but it will still need to be removed and that is the job of the power washer.
When it comes to power washers it is all about BOTH the PSI -and- the Gallons per minute.
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Joseph Meehan

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too much pressure can roughen concrete, creating permanent marks and easier mold re growth.....
you have been warned
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Agreed, but followup with a concrete sealer should also be considered.
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On Wed, 5 Mar 2008 13:58:11 -0800 (PST), BobR

I hope the OP gets the burns out of the concrete:)
Pressure washers, won't cut it.
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Very true. Most powerful machines have a means of reducing the pressure or you can simply stand back a little more. But if the machine does not have what it takes to start with, there is nothing you can do. Frankly most people only look at the psi and never give a though to the volume. The real point I was trying to make was to be sure to get enough pressure and don't ignore the volume as most people tend to. Most consumer machines have OK pressure and poor volume.
I should have been more clear with my original answer.
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Since most posters suggest pressure washing, would my 1800 psi 1.7 Gal/m washer hack it? Might be worth a try.
Otherwise, I guess I could stain or paint the concrete to make the blotches look more uniform.
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never ever paint concrete, its a slippery every year maintence issue......
whatever you do the seeds, which i am not familiar with can do it again.
some things are better ignored because the possible fixes arent wort the money time hassle and dont last
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Walter R. wrote:

washing. Trouble with concrete is that you can write your name on it with the pressure washer, eroding the concrete, and not get all the stains. I would try scrubbing with 1:10 bleach/water, or just hose it on with a hose end sprayer. Bleach doesn't bother our plants, as I have used bleach on the outside of our condo, but I would rinse area well. For the burn marks, if there aren't too many, you might try some acryllic paint to camouflage them........I did that on a concrete deck in our atrium after a neighbor got walnut stain all over it. It is sheltered and not a lot of sun or weather, but it stays on concrete. I used small bottles of craft paint and just mixed it to get the color right.
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Stain maybe if you get that concrete really really clean first. Don't paint. The only painting of concrete I would recommend is the cement floor of a garage and then only if you are ready to do the intense prep that it requires for a good job and if you buy the expensive top quality true two part epoxy materials.
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Will commercial sandblasting work?
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Sandblasting certainly will get it clean. However even home sandblasting can damage the concrete. They typical sidewalk will have been finished to bring some "cream" to the surface of the walk to provide a strong smooth surface. The sand blaster can eat through that.
I would reserve it for the final try. I have some curbing that has been very difficult to clean. I have been holding off getting the sand blasting outfit out, but I may do it this summer. I will cut back on the power however.
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wrote:

Probably not, but the chlorine may harm other things in the runoff (trees, shrubs, grass, metal, etc). I wouldn't go any higher than 1 cup Clorox per gallon of water. A pressure washer with plain water is the tool to clean concrete.
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Don't waste your time. Go to a janitorial supply store, rent one their hairiest power scrubbers and buy the compound they recommend for cleaning concrete. Take it home and work your butt off (been there, done that). Rinse it off and let it dry, then if it looks decent, apply a sealer from the J. S. store. If successful, take better care of the walk. If not, tear up the walk and replace with something more compatible with your eco system, like pavers or some such. HTH
Joe
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Walter R. wrote:

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