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One for the woodworkers

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One for the woodworkers

Old 25th May 2015, 09:37
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One for the woodworkers

Last November I bought a wooden sailing dinghy which was in need of a little TLC. On inspection it proved to be sound and solid but there had been an issue with much of the varnish on the topside decks and cockpit areas. The previous owner had had the boat re-varnished and in only one season of use the problems start to show up. After that the boat had been sheltered in a car port for a few years as the owner lost interest. There were some areas where the varnish had just flaked off completely and the wood had become a little faded due to the effects of UV exposure. There were other areas where water had crept under and sat there and the wood was stained darker. I found no evidence of actual repair work or any form of filler use.

So I set too with a wallpaper scraper and in a couple of evenings had scraped all of the problem areas back to bare wood. The varnish, in the main, came away in flakes, some as big as your hand. Clearly it was an adhesion problem. The underlying wood is still sound with no soft or porous areas.

At the local chandlers I told the chappie what had transpired and he suggested that it is likely that the boat is made from teak plywood which is sort of oily by nature. This can cause issues with varnish but if you thoroughly wash the surface of the wood with a good thinners and then use the right varnish it should adhere properly.

I did use a good thinners and I did use the right varnish but yesterday I started to feel that the surface of the varnish on the side deck areas has become less than smooth and may be starting to crack along the grain in the wood. The boat has only been back in regular use for six weeks having been in dry storage since December.

I don't know what to try next?

Anyone?

Rans6.......
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Old 25th May 2015, 09:48
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Going back to when I was a youngster we used to spend hours varnishing our sailing dinghies, a mixture of shearwaters, fireballs, ospreys etc.. We would apply up to 20 layers of varnish to give a very good wet deep looking finish. The first coat needs to be applied mixing the varnish with thinners at a 10:1 ratio, i.e. One part varnish to 10 parts thinners, then 2 parts varnish to 8 parts thinners, sanding down between coats. Laborious but worth doing.

How to Varnish Wood on Boats
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Old 25th May 2015, 09:51
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Andrew did you thin the varnish? Thinned it is absorbed into the wood. A few thinned coats and a couple of unthinned top coats of yacht varnish should do the trick.
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Old 25th May 2015, 10:02
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Caveat: Although I've owned several wooden boats, my woodworking expertise is to do with items for interior use.

I agree with your chandler's diagnosis. What sort of thinners did you use? On solid wood I would use acetone rather than paint thinners, but I don't know what effect this would have on the glue used in the plywood. Try it on a test piece first. Methylated spirits is probably a safe alternative.

Any small splits in the wood will trap moisture, and although marine finishes are pretty good, short of sheathing in fibreglass, there's nothing I know of that will completely stop ingress of water. (I'm not even sure about fibreglass.)

The process I use is as follows:
Sand to a smooth finish, say 250 grit. Clean all the dust off with a vacuum cleaner then tack cloth or paper towels dampened with turps.

Rub in an oil-based wood grain filler using hessian. Rub it in well so there is as little as possible on the surface. If you decide to tint the filler, make it slightly darker than the wood, rather than lighter.

After the filler has dried, sand to the desired finish, using a succession of grits. I use up to 800 grit, but you probably aren't going to want that on the topsides of a boat unless you're as anal as I.

Clean all the dust off again using a vacuum cleaner and tack cloth.

Clean the surface using a cloth or paper towel and acetone.

Brush on a thin coat of shellac and allow to dry for several hours. It will feel touch dry on a few minutes, but trust me on this, let it dry for a couple of hours. This raises the wood fibres and hardens them.

Lightly sand the surface using whatever your final grit was, and wipe the dust of using a cloth or paper towel dampened with turps.

You can now finish the surface using whatever marine finish you prefer.

This may sound fiddly. It is, but it's worth doing properly.
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Old 25th May 2015, 10:02
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Use proper, porous, yacht varnish. Polyurethane is the kiss of death on wooden boats, at least on surfaces exposed to the sea, sun and wind. I think it's possible that what you found was the remnants of a polyurethane varnish.

Of forget varnish altogether, as I did, especially if you are looking at an oily hardwood like teak or iroqo, or even mahogany, and when you are down to clean bare wood start soaking it in Deks Olje No. 1, changing to No. 2 when you have reached saturation point with No 1, and have let it dry out a bit. Continue with, say, 6 - 10 applications, and you'll have a lovely, almost maintenance-free, surface for years. Just a rub over with No 2 every Spring and you are all set.
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Old 25th May 2015, 10:07
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I followed the thinning guidelines on the varnish, the first layer was not as dilute as 10:1 though. I only got as far as 6 layers, rubbing down after every other one. The major problem was getting my workspace warm enough for the varnish in the middle of November. If it is turning as bad as before I might have to take a week off from sailing in August or September and re-do the affected areas. At the moment that seems to be just the side deck/gunwhale area. Not too big a job.

The dinghy is a Phantom single hander. I had originally intended to buy one of the later epoxy resin "plastic fantastic" ones but they are several orders of magnitude more expensive than my wooden one and at the time I didn't know whether I would like the class. Last year I found out the hard way that a [email protected] dinghy isn't suitable for someone of my height, my weight, my lack of suppleness. This Phantom was a very cost effective way to try the boat for a season and I'm happy to put in a little time and effort to keep it worth more than I paid for it.

Ta,

Rans6....
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Old 25th May 2015, 10:07
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Capot, interesting that you suggest an oil finish. That is, without doubt, my preference for the interior work that I do, from both a practical and aesthetic point of view. I'm pleased that it's recommended as a marine finish too.
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Old 25th May 2015, 12:25
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Epifanes is very particular about prep and coating sequence over teak.

Most tropical woods, as soon as the surface is prepped you have to immediately get the first coat of finish laid on or you have to prep again to preclude formation of the oily boundary layer between the wood and your finish.

Painting Wood - Epifanes NA Inc.
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Old 25th May 2015, 12:49
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You really need to be certain what species of wood you are dealing with. If it really is a veneer of teak - and it may no not be given you comment about water darkening patches of it - I would try Tung Oil. I stripped a big boat once, with so much varnish on it that timber we thought was a dark golden colour turned out to be almost white (it was Queensland box). We ended up giving the whole coach roof a couple of coats of Tung Oil. Halfway through the season, it had begun to 'wear off', which is a characteristic of Tung Oil in a sea environment, and we coated it again. No more stripping back, just a light sand - and you don't even have to do that if you don't feel like it.

By contrast, I sailed on a Dragon, built by Borresan of Denmark. It was mahogany, all varnished. Every winter we spent hours compensating the skipper for our pleasant season's sailing by varnishing his beautiful boat. It was referred to as the 'floating piano'; very impressive, but at some cost!
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Old 25th May 2015, 16:55
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Oil vs. Varnish

Varnish sits on the surface, eventually cracks and has to be sanded off or stripped completely before revarnishing

Oil penetrates, but eventually water leaches it out. But renewal is simpler with a quick scuff and reapplication

The trick is not letting it go too long
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Old 25th May 2015, 23:33
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I'm a traditional wooden boat builder by trade (though no longer work in the industry)
I can only echo some of the comments on here.
Exterior woodwork.........go for a good quality oiled finish.
I would also recommended Deks Olje
Maintenance is easy......once a year with a light rub down and re-oil with a couple of light layers.
Leave the yacht varnish for internal joinery.........which you won't have in a dinghy!
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Old 25th May 2015, 23:38
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As an addendum.......the varnishing techniques described by previous posters are spot on. Greatly thinned layers with de-nibbing between each coat is the way to go if varnishing.
However, if you do have teak then, it doesn't take varnish well....Iroko doesn't either.
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Old 26th May 2015, 09:01
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Back in the day, at the Sailing Club at Marham we used best quality RAF Seaplane Varnish!

This was obtained from stores for for the legitimate purpose of coating external aerials on aircraft.
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Old 26th May 2015, 12:04
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I quite like the Deks Olje idea. The data sheets for the products suggest NOT using the number 2 stuff for decks and walkways as it may become slippery when wet. Not a good idea in a boat where you crawl/kneel/stand/sit and generally try to shuffle about without using your hands to get up. Foot grip is very important as your hands are both otherwise engaged with the tiller and mainsheet.

Is it OK to just go with liberal coatings of the number 1 stuff and re-apply often? I am only contemplating fresh water usage. Adding grip tape after oiling sounds like a "not going to work" idea.

Ta,

Rans6.....
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Old 26th May 2015, 14:40
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...suggest NOT using the number 2 stuff for decks and walkways as it may become slippery when wet.
Absolutely right in a cruising boat, don't even think of doing that. How that works in a dinghy I wouldn't know!

I agree about the tape.

No 1 on its own is very thin and gets absorbed, but I guess if you apply enough sooner or later it would form a surface of sorts. I've never tried that. When/if it does it would probably be slippery when wet.
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