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Thread: Oxalic acid and Redwood?

  1. #1
    Join Date
    Mar 2006
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    Oxalic acid and Redwood?

    I picked up this 4x4 and 2x6 B redwood yesterday and gave it a wash using Oxiclean to get the dirt and mildew, then an oxalic acid wash using 2 cups acid to a gallon of water. The 2x6 came out nice but what happened to the 4x4, it’s all black after the oxalic wash.
    IMG_5665.JPGIMG_5666.JPG

    Any remedy for this or do I need to sand it all out?

    I'm reading up on it now and came across this rinsing Info which I've never done using oxalic acid before-
    'Mix a neutralizing solution of ammonia and warm water, or Borax and warm water, in a plastic bucket and thoroughly rinse the wood surface.'
    WoodsShop

  2. #2
    Join Date
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    It's most likely some form of contamination in the old timber. It may not sand out, in fact it looks quite deeply entrenched. What you see is what you will always have.

    I am not in the habit of using any chemicals to clean timber but in this case I don't think it is your fault as the rest of the job is OK. If something must be cleaned, I recommend fresh water and a scrubbing brush or if it is really bad, use a pressure washer. Cheers
    Every construction obeys the laws of physics. Whether we like or understand the result is of no interest to the universe.

  3. #3
    That looks more like fir than red oak to me.

    But that black staining is common for red oak. It can happen upon exposure to iron. What did you use to apply the wash with?

  4. #4
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    This is new Calif. redwood, and oxalic acid is also called a wood brightener or wood bleach and shouldn't have done this.
    Last edited by Joe Wood; 01-13-2019 at 11:43 AM.
    WoodsShop

  5. #5
    It is hard to bleach green red oak. Are these properly dried? The water in the lumber is your enemy for staining

  6. #6
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    This is Calif. redwood not red oak and yes they are pretty dry.
    WoodsShop

  7. #7
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    Guys, redwood, not red oak. Even this far away I still get to use redwood from time to time. Joe, I really don't think the oxalic acid did this without the presence of some other contaminant. If it is new timber, get back to your supplier and ask for an explanation as to why they shouldn't replace it. Cheers
    Every construction obeys the laws of physics. Whether we like or understand the result is of no interest to the universe.

  8. #8
    Aha !!! Makes way more sense. I thought it looked like fir!!! Thanks, Wayne
    Last edited by Prashun Patel; 01-13-2019 at 11:05 PM.

  9. #9
    Join Date
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    I used to clean my redwood fence with oxalic acid and it always made it bright and new looking again. So I have to think the piece you had that went wonky either is not redwood or is contaminated with something oxalic acid reacts with in a negative way.

    John

  10. #10
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    Yeah you see in the 1st pic the 2x6 and 4x4, both were washed the same. I'll probably end up planing it down a bit and routing the edges again, but will wait to see what my supplier says. Looks like iron stain but that's what oxalic is supposed to take care of.
    WoodsShop

  11. #11
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    some better pics, the 2x6 is on the left.
    Attached Images Attached Images
    WoodsShop

  12. #12
    Join Date
    Dec 2004
    Location
    Cincinnati, OH
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    379
    Please let us know how it turns out. Thanks
    Rustic? Well, no. That was not my intention!

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