Oxalic acid and Varnish

westernman

westernman

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I have some discoloured bits on my mast where water has got under the varnish. After I have scraped off the old varnish I was planning on putting some oxalic acid on this to reduce the discolouring.

How fastidous do I need to be about washing away the oxalic acid before putting on the varnish?

Best of all I would like not to wash off the oxalic acid at all (it will end up going all over the deck etc), and plonk on the varnish on as soon as it is dry. I will be using Tokinois.
 
I've always thoroughly washed the acid away.
Unless, for some reason, you don't want to get your decks wet at the moment, if you use plenty of water any acid will be so dilute by the time it gets on deck that it won't cause a problem.
 
michaelchapman said:
I have some discoloured bits on my mast where water has got under the varnish. After I have scraped off the old varnish I was planning on putting some oxalic acid on this to reduce the discolouring.

How fastidous do I need to be about washing away the oxalic acid before putting on the varnish?

Best of all I would like not to wash off the oxalic acid at all (it will end up going all over the deck etc), and plonk on the varnish on as soon as it is dry. I will be using Tokinois.
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Advice on using oxalic acid here http://www.agwoodcare.co.uk/more_info_oxalic.html

safety data here http://www.agwoodcare.co.uk/COSHH/Oxalic Acid.doc

My "Woodworkers Pocket Book" suggests neutralizing with borax (1 oz per ½ gallon) then rinsing with water and drying
 
I quite often leave it other than a wipe with a rag of white spirit. It probably effects the finish slightly, what with the crystals but not enough to bother me. I find it handy if it's likely to rain before you have time to get a full coat on as quite often even with 50-50 the wood discolours again if it gets wet. With oxalic acid still applied though it is self solving.
 
Woodlouse said:
I quite often leave it other than a wipe with a rag of white spirit. It probably effects the finish slightly, what with the crystals but not enough to bother me. I find it handy if it's likely to rain before you have time to get a full coat on as quite often even with 50-50 the wood discolours again if it gets wet. With oxalic acid still applied though it is self solving.
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My main concern is that there is some nasty chemical incompatibility with the varnish.
You seem to be saying that there is not.

I am tempted just to wipe over it once it is dry with methylated spirits, and then let that dry before plonking on the varnish.
 
VicS said:
Advice on using oxalic acid here http://www.agwoodcare.co.uk/more_info_oxalic.html

safety data here http://www.agwoodcare.co.uk/COSHH/Oxalic%20Acid.doc

My "Woodworkers Pocket Book" suggests neutralizing with borax (1 oz per ½ gallon) then rinsing with water and drying
Click to expand...

Time to change your book I think. Borax is now considered to be a "substance of very high concern". it is thought to damage fertility and have other effects. Oxalic acid can be removed by water easily and does not need to be neutralised like strong acids.
 
nigelmercier said:
More EU H&S bollox, it's in loads of things, even food as E285.
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At low concentrations is is not harmful. However above about 5% it is and strictly controlled nowadays. Although I agree that many eu rules are over the top, this one is correctly researched in my opinion. Borax was banned for use in food many years ago except some minor uses. Best not to steal the thread tho'.
 
cliveshelton said:
Time to change your book I think. Borax is now considered to be a "substance of very high concern". it is thought to damage fertility and have other effects. Oxalic acid can be removed by water easily and does not need to be neutralised like strong acids.
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cliveshelton said:
At low concentrations is is not harmful. However above about 5% it is and strictly controlled nowadays. Although I agree that many eu rules are over the top, this one is correctly researched in my opinion. Borax was banned for use in food many years ago except some minor uses. Best not to steal the thread tho'.
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The very dilute solution suggested then is no problem and surely less of a danger to the user than the saturated solution of oxalic acid used for bleaching the wood in the first place!


5% of borax in some sugar syrup makes jolly effective ant killer!
 
michaelchapman said:
My main concern is that there is some nasty chemical incompatibility with the varnish.
You seem to be saying that there is not.

I am tempted just to wipe over it once it is dry with methylated spirits, and then let that dry before plonking on the varnish.
Click to expand...
I've noticed no nasty reactions. Both oxalic acid, and varnish are fairly inert ultimately, and especially so when dry.
 
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