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  1. #1
    stuball48 is offline Stainless
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    Default OT: Advice needed on cleaning concrete patio

    Volunteered to clean a patio for elderly lady from church. It is a concrete patio (15' x 30') with two or three years of mold and mildew. I have a small pressure washer. Is there a mixture of anything to spray on the patio before cleaning? Or is "time and effort" all that is needed? Your opinions are always helpful. Thanks

  2. #2
    Tom1 is offline Stainless
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    If its mold and mildew, mix a fairly strong mixture of cheap bleach and water. Use a garden sprayer to soak down the patio. You will need PPE for this also protect other things you dont want bleach on, plants etc. You will see the bleach kill off the mold in front of your eyes, you will even see where you missed a spot. Let it sit a few a short while, then pressure wash. Should come clean pretty quick. I have had trouble just trying to pressure wash that stuff off. Also if you dont kill it with the bleach, it seems to come back fast. I guess your just taking the top of the growth off leaving the root behind so to say. Depending on your washer, if you can used a "turbo" nozzle it will speed up the job, ALOT.

  3. #3
    Motomoron's Avatar
    Motomoron is online now Hot Rolled
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    Precisely correct.

    Get a gallon of the cheapest bleach there is, dilute it 50% or better and slosh a coat over the whole thing. The mold and mildew will disappear as you watch. Pressure wash after, preferably w/ "turbo" nozzle. When it dries it'll be so bright you'll need shades.

  4. #4
    Hdpg is offline Stainless
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    You won't hurt the concrete even using un-diluted bleach; just wear old clothes because they are going to get bleached spots.

    And I know the others have suggested pressure washes but at first go very cautiously in an inconspicuous corner otherwise your elderly lady may end up with an exposed aggregate patio.

  5. #5
    67Cuda's Avatar
    67Cuda is offline Titanium
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    How many psi is your pressure washer and what type of tip are you using? I clean my concrete each spring, 2300 psi, and some parts of it are fairly grimy, I only use water and it cleans it well enough to not have to fiddle with chemicals. Spot clean what you think is the worst area, see how it looks and go from there. Sounds like you doing a good deed, no need to knock your self out, not like you doing it for money and need the best results.

    Tom

  6. #6
    Bill's Machine Shop is offline Hot Rolled
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    Before using bleach, consider where it will go after it's rinsed away. I don't know the halflife of bleach, but I do know that if it gets into a septic system, it will take a long time for the system to return to normal because the bleach kills the useful bacteria. If the bleach is rinsed into a garden, it will likely kill your old lady's prize flowers. I'm with 67cuda. A pressure washer will clean the dirt out of the little pockets in concrete very effectively without chemicals. An alternative might be one of those biodegradable dilutable cleaners. WWQ

  7. #7
    vraptor is offline Cast Iron
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    There's some stuff called Jo-max that's supposed to intensify the effect of the bleach. I never had much luck with it, but they may have improved the product since I last used it. One thing you might try is after the patio is cleaned and dry, go over it with a mild fungicide. Fungi have a root system called mycelium that is hard to kill and will penetrate to a surprising depth in most hard surfaces. This will keep you from having to go back to re-do the job.

  8. #8
    David/toledo is offline Hot Rolled
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    If it is grim it should just wash, off even at 1500 psi. The bleach is good to but wet down any plants around the deck. To stop from killing them.
    David/toledo

  9. #9
    John Gargano's Avatar
    John Gargano is offline Aluminum
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    Default Muriatic Acid

    Another item to consider is muriatic acid. Get a plastic bucket and put in water first. Then mix the muriatic acid (actually a weak solution of hydrochloric acid) at a ratio of 16 water to 1 muriatic acid. Using rubber gloves, and a masonry brush at the end of a handle (they make such a thing specifically for this purpose) dip the brush into the solution and vigorously brush the surface. Let it stand a bit to allow it to react and form a powdery residue (calcium carbonate).

    Before doing this saturate the surrounding area with water. This will keep the acid solutioin from killing the grass. When finished, sprinkle some baking soda on the surface and scrub it around with the brush to neutralize the acid - this basically forms water and a mineral salt -both of which are totally harmless and much less toxic then bleach.

    The surface will then be clean and if desired, you can paint it with any type of concrete paint. I prefer to leave it alone as paint on concrete can be slippery.

  10. #10
    stuball48 is offline Stainless
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    The concrete patio is clean and I had a pressure washer with 2450 psi. All I needed was the water--no chemicals of any kind--and on each pass it looked like an old chalkboard being washed in the country school---I made a road each pass. Thanks to all for the suggestions.

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