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Thread: How can I get spilled concrete off a boulder?

  1. #1
    Join Date
    Oct 2006
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    Placitas, NM in the foothills of the Sandia Mt
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    688

    How can I get spilled concrete off a boulder?

    Had a landscaping crew out a week ago to build a garden wall out of block covered with adobe. Just noticed that a boulder that was near their mixer got splashed with some concrete. I tried washing the boulder with a stiff brush, but no luck.

    Any ideas how I can get this stuff off?
    Thanks in advance!
    Don't believe everything you think!

  2. #2
    Join Date
    Dec 2006
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    Nova Scotia's beautiful south shore
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    Depending on what the bolders are made of in your part of the world, muriatic (HCl) acid is the old standby for cleaning mortar, grout and concrete from surfaces.

    If the bolder is hard like granite, no problem. If it's limestone you'll need to be on your toes. The acid might eat the bolder quicker than the spill.

    You can buy muriatic at building supply stores.
    All the best,
    Ian G

    **Now holding auditions for a catchy new signature**

  3. #3
    Join Date
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    Maybe a sandblaster?
    A very wise man once said.......
    "I'll take my chances with Misseurs Smith and Wesson. "

  4. #4
    Join Date
    Nov 2006
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    Albuquerque, New Mexico
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    Jesse, depending on how thick it is, you could try some Muriatic acid.
    "I am enclosing two tickets to the first night of my new play; bring a
    friend...if you have one."
    --George Bernard Shaw to Winston Churchill

    "Cannot possibly attend first night, will attend second..if there is
    one."
    --Winston Churchill, in response




  5. #5
    Join Date
    Oct 2006
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    ozarks
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    cold chisel and a small sledge.
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  6. #6
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    Arena, Wisconsin
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    Hey Jesse, muriatic acid is indeed the ticket, but google it and heed the precautions for handling. The best source is swimming pool supply stores.

    Iíve used it for exposing aggregate on concrete slabsÖ which makes me think that our resident mud head will have some really good advice for you when he logs on.

    If you have near the variety of rock in NM that is found in AZ, then you might well heed Ianís admonition to stay on your toes if it is limestone. If it is, then I would chip off splatters and apply the acid with a spray bottle. Keep the hose handy.

  7. #7
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    Rock hammer.

  8. #8
    Join Date
    Nov 2006
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    S E Nebraska
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    muratic acid is usually mixed with water to dilute it before use, scrubbed with a stiff brush and washed off quickly for brickwork, try a butcher block wire brush and straight vinegar.
    Drawknife, Spokeshave, Plane, Rasp; Decisions, decisions.
    Old tools are all very MODERN, they are all CORDLESS.
    By Hammer and Hand All Arts Do Stand.

  9. #9
    Join Date
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    ABQ NM
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    As has been suggested, I'd use a rock hammer and chisel to get the big stuff off, then muriatic acid and a stiff brush as others have suggested. That Sandia granite won't flinch when the acid hits it. When I was in the concrete testing business (in Albuquerque), we'd also use hydrochloric acid to clean up our testing equipment, but that's some nasty stuff, so I wouldn't recommend it.

    Frank, my dad helped pioneer exposed aggregate cast-in-place concrete slabs when they built the Air Force Academy in Colorado Springs around 1957. That was the first in-place application of the technique.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  10. #10
    Join Date
    Dec 2006
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    Nova Scotia's beautiful south shore
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    Muriatic is the ancient name for hydrochloric acid (think alchemy). These days it's how we refer to a fairly dilute (10-12%) concentration of HCl used as a cleaning aid. Concentrated industrial HCl is in the range of 38%.

    Even home store muriatic at 10% or so needs to be further diluted. Follow safety instructions, pour acid into water and not vice versa, wear gloves and goggles.

    Here's the EPA bulletin with full details Link

    Have you thought about blasting the boulder out, Jesse ?

    Table vinegar is approx 4% acetic acid - pickling vinegar is about 6%. I think it would likely evaporate long before it did anything to concrete. Could be wrong, tho.

    I am not a chemist, but I did play one in high school. (and Wikipedia is my friend )
    All the best,
    Ian G

    **Now holding auditions for a catchy new signature**

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