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  1. #1
    Chrusty 1 Guest

    Default Removing fastening stains?

    Hi all,

    A mate of mine has a nice little mahogany clinker launch, that we want to spiffy up a bit, we are intending to take off all the old varnish, which is long past it's use by date, and start again doing the job properly. One of the problems that we will have to deal with, is that the areas immediately around the fastenings are stained black, now someone has told me that once we are back to bare wood, we can bleach out these stains using oxalic acid? So my question is, is this the way to go about it, or is there a better way?

    Regards, Chrusty.

  2. #2
    Join Date
    May 2010
    Location
    portsmouth,UK
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    577

    Default

    Oxalic acid is perfect for the job, i've used it lots in the past before, It removes blackening of wood and rust stains from everything and its very good at brightening yellowed fiberglass too, and i still have 4 kilos of the stuff which i just brought aboard my new boat to clean it with when i eventually get around to it

  3. #3
    Chrusty 1 Guest

    Default

    Thanks for that mate, but may I ask, what is the best way to apply it, make a paste and just gob it on? Leave it for how long?

    Regards, Chrusty.

  4. #4
    Join Date
    Jan 2006
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    Behind your curtains.
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    8,295

    Default

    Best way to apply oxalic acid is to dissolve the crystals in hot (but not too hot) water until the solution is saturated and then just slap it on with a brush. Keep on applying until you are happy with the results as it will only work when wet and then wash off with fresh water.

    Can't promise you it will work on the staining around the fastenings though as I believe that's caused by a galvanic reaction between the wood and the iron. Not simply the result of weathering or damp. However, the acid will not do any harm and should remove the majority of other marks and stains in the timber.

  5. #5
    Chrusty 1 Guest

    Default

    Hmmmmm, ok, the fastenings are copper though, not iron. Is it the same cause?

    Regards, Chrusty.

  6. #6
    Join Date
    Jan 2006
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    Behind your curtains.
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    Default

    If the fastenings are copper you may well be in luck. It's certainly worth a try and will not make it any worse.

    One thing about mahogany is that it will change colour to a dark brown when it's been scraped, sanded and freshly varnished. Then with time the sun will bleach the wood beneath the varnish to a much paler shade. It means that damage to the varnish and touch ups will generally stick out like a sore thumb, but if you start the whole thing from scratch then it should look pretty damn good.

  7. #7
    Chrusty 1 Guest

    Default

    Thanks Woodlouse, but two more questions if I may? (my brain isn't working very well this evening). What ratio acid crystals to water is best? Oh yes! Where is the best place to buy oxalic acid?

    Regards, Chrusty.

  8. #8
    Join Date
    Jan 2006
    Location
    Behind your curtains.
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    Default

    The ratio is simple. Keep adding them until they stop dissolving. The stronger the better basically.

    As for buying it, a chandlery should have it, if not then they should definitely be able to tell you where to get some locally. I'm afraid my minds not firing on all cylinders either at the moment so I can't think where else would sell it at the moment.

  9. #9
    Chrusty 1 Guest

    Default

    Cheers Woodlouse and Top Donkey for your replies, very helpful.

    Regards, Chrusty.

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