Oxalic acid

T

TimLamb

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I am applying it to a tiller that has some watermark stains.
I am told that the tiller is teak, although I'm not sure, but it's a lightish coloured solid piece of wood.
The first few applications of the acid and water don't seem to make any difference.
My question is - can I overdo it and cause permanent damage, or can I leave the solution on for a longer period (say overnight) to see if that helps ?

Thanks in anticipation.

TJL

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Tim,

What strength are you using it at? You need to make up a saturated solution, i.e. dissolve the acid crystals in water till no more will dissolve. Less than that and it's a bit feeble. Even that strength wouldn't touch a black waterstain I had in some marine ply. Maybe your tiller has some sort of treatment on it which is preventing the acid working?

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25 g in 1/2 litre (from a post I found by searching)
Tiller scraped and sanded back to new wood
It doesn't look too bad to be honest - I was just hoping to make it perfect.


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Suggest you make up a 'wet' paste and leave to dry until crystalises. Found that you often need several aplications for deep stains. When you remove the dried crystals, wash off with fresh water and start again if stain not gone.

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Unless you are somewhere warm it might not work. Anything below 60F and you'rer wasting your time.

Steve Cronin

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You've got the right recipe - I posted it a while back. There's no harm in strengthening the mix a little but as others have said you'll need repeated goes to get at bad stains and warm days definitily help.

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Remember Oxalic acid is a powerful poison. Wear rubber gloves and take great care that neither you nor anyone else ingests it

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Franklin's tip about wallpaper paste is a good un. You can also make a very cheap and effective paint stripper using caustic soda solution and wallpaper paste. Ok it's got nothing to do with stain removal but might be helpful to someone.

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This might well be of interest to me. Anyone know how GRP stands up to caustic soda, and how strong should the soda be??

By the way, the two-part wood bleach that Rustins and others sell for a small fortune are:

Part 1: Caustic soda (Not sure how strong. I made up a 10% solution and it seemed to work - add 100g of caustic soda drain cleanr to a litre of water, NOT the other way round or it could boil up in your face)

Part 2 100vol Hydrogen Peroxide ( I could only get 50 vol from my local chemist, and it was a bit feeble.)

Paint on part 1, leave to soak in the wood, paint on part 2, leave an hour or so and wash off. Neutralise the alkali with vinegar in water then wash with clean water.

This will get rid of wood stain, and may well have the desired effect with water stains as well. As with Oxalic acid, rather unfriendly, so rubber gloves, safety glasses and common sense are the order of the day.

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Sorry, don't know about Grp, nasty modern stuff that it is. I'd be inclined to test it on something not too important first before attacking your hull with it. I cant remember the exact quantities but I would keep adding it to water and dipping a painted bit of wood for a few minutes till it's strong enough to start to dissolve the paint, then add your paste to bring it up to a gel like consistency. If you've got a rainwater butt, you can mix up a strong solution and dip n strip smaller items. That's all the commercial stripping joints do. Always wear protective goggles and good rubber gloves when using caustic soda and make sure it's washed off using copious amounts of water afterwards. A scrubbing brush or a pressure washer on a low setting is very good at getting the last clingy bits out of nooks and crannies. Caustic soda can darken some timbers, especially softwoods. I dipped and stripped all my stair spindles (scots pine) they came up a lovely dark antique pine colour when subsequently varnished.

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