oxalic acid on mahogany cold moulded

Lloydus123

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hi, ive just stripped down my topsides of old varnish to attend to some seams and what not, I have a lot of water ingress marks , and the topsides are thin enough . so I'm looking to take to the route of oxalic acid to get the topsides looking there best again, my primary concern is the introduction of a large mouth of fresh water to the bare topsides in washing down . but I feel this would be less damaging than sanding more thickness out of my already thin topsides . does anyone have any advice or experience with this process before .


my plan is
very light sand to remove residue
oxalic acid
3 coats of epoxy
3 coats of epiphanies varnish (minimum)
I'm going to use epiphanies wood finish as you can redcoat without sanding pithing 72 hours accounting for 12 hours cure time


any comments on any process would be appreciated also
regards

Lloyd
 

tillergirl

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Gosh, there is so much in that question. How badly marked?

I have used oxalic acid on teak, iroko and spruce (spars). Depening on the extent of the marks you will need repeated acid application. And you will still need to sand down after the acid. Here is a series of images:

Before attention

Laying Up 2011 037 by Roger Gaspar, on Flickr

Varnish removed by hot air gun

Laying Up 2011 040 by Roger Gaspar, on Flickr

After repeated acid applications. I think it was 5 or 6 applications. I could have made a stronger mix but preferred to do little and often. Of course I had the option of turning the spar for applications.

Misc 2011 050 by Roger Gaspar, on Flickr

Sanded

Misc 2011 048 by Roger Gaspar, on Flickr

10 coats of Epifanes Clear Varnish

P1010094 by Roger Gaspar, on Flickr

After 3 years of use. Note the spinny pole behind the boom

P1010059 by Roger Gaspar, on Flickr

How the spinny pole was in 1991 when I bought the boat. All is possible.

DSC30254 by Roger Gaspar, on Flickr

Personally I would not use epoxy. Tried that once on the coachroof; nothing but an appalling finish. Epifanes Wood finish is designed for Teak and iroko. I used Epifanes Wood Finish on the cockpit (iroko) - excellent for that, tough, rapid application (ditto for the handrails). Touching up is good and easy. It isn't quite such a good finish as the proper varnish. Please, please cut out that epoxy nonsense (I hate it in that sort of application I admit). The 3 coats of Epifanes would be far, far better.
 

Lloydus123

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appreciate the pictures, lovely job and a great finish you've achieved there. I would like to pick you brains on your beef with epoxy. my thinking was to completely seal my hull from water ingress, and use varnish as a uv layer. I have done similar with my coach roof , but I used bonda g4 wood seal, in replace of epoxy and it looks great, just not so cost effective for the hull . its similar in the way that I can apply 3 coats in one day, which I like a lot. epiphanies wood finish is especially good on iron and teak as per the can , but after speaking directly to epiphanies they assured me an equally good finish as plain old epiphanies, my angle was, eliminating sanding

regards

Lloyd
 

Lloydus123

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also 3 coats of epiphanies on my top sides, wouldn't last very long , I would only be getting past the thinning down process at that point , I'm looking at 6/7 coats of varnish minimum without epoxy
 

tillergirl

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I admit the Epifanes clear varnish needs maintenance - well everything does but a top quality finish like Epifanes varnish would need an annual topcoat.

The Woodfinish is good and pretty tough. When I applied Wood Finish I followed the instructions to the letter, one coat thinned 50% of Wood Finish and then 4-5 standard coats and within 72 hours I didn't need to sand. That was for iroko. But the manual has different instructions for Mahogany. It says follow the 'standard' varnishing instructions which is cost no 1 at 50%, coat no 2 at 25%, coat no 3 at 15%, then standard coats. And it says for Mahogany it needs 8 to 10 coats! I think this is because Wood Finish is designed to 'breath' - Teak and Iroko needs that but Mahogany doesn't need to breath and so the extra coats of Wood Finish I think might be necessary to 'seal' the Mahogany.

As to the epoxy, I think using the epoxy as a sealer is preventing the Wood Finish or indeed the Clear Varnish to proper adhere to the timber. Of course the epoxy needs to be coated because of UV but the Wood Finish isn't designed to adhere to epoxy. Will it work or will it not? I don't know you would need to ask Epifanes.
 

Tranona

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Another vote for avoiding epoxy in this situation. Difficult to get a good surface if you are then going to varnish, potential problems with amine blush and then adhesion of the varnish to the epoxy. finally no matter how good the UV filter eventually the epoxy will cloud and go yellow and there is nothing you can do to recover.

My preference for coating would be Cetol HLS followed by Cetol No7 plus
 

DownWest

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Alternative point here: If the finish with epoxy is the problem, then try Resoltech's water based one. First coat onto sanded wood is one part resin/one part hardener/one part water. Second coat, halve the water. Third, just the resin and hardener. It goes on like water based varnish and give a good finish, drying in under an hour. Coats are slightly milky until it starts going off, helps with seeing where you have been.. Then a decent UV barrier varnish to finish.
My little ply double-ender was finished with the three coats and nothing else as I was in a rush to get to a festival. Kept under cover, the hull is still OK, while the coamings & spars etc have been refinished a couple of times in 12 yrs. Not used her much the last couple of years, but will get down to refinishing the hull in paint now.
Worth considering & they have a UK agent.

Edit:
Web page: Epoxy
The stuff is Re. 1010
 
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arcot

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Perhaps try
Hydrogen peroxide to fix the stained wood
Then epoxy followed by many coats of uv protected varnish after washing the epoxy to remove amine.
 
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