varnish stripping

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rocketman

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my clinker ply dinghy (1964) - used for cruising rather than racing - will soon be in the shed for tlc. last winter (our first) got the hull painted, and a few small repairs and improvements seen too, and she looks a treat. this year I need to revarnish her inside. current varnish is in mostly good nick, just rubbing a bit thin here and there. Trouble is, I have no idea what the original varnish is, so not sure whether I need to strip it all off, or just rub down. If stripping, what method have people found most effective? I also coated one shortish section - eighteen inches - with epoxy to seal a split in one of the boards - this has worked well, and looks neat, but will varnish take to this? aside from conventional varnish, any suggestions for a hard-wearing finish?
any advice appreciated.


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Stripping varnish is hard work, so if the underlying coatings are really sound, don't bother. If not, the only tool to use is a hot air gun and a tungsten carbide scraper, maybe cleaning up with a bit of varnish stripper and a nylon pan scourer. You can check the underlying coat by testing a sample with the varnish you are proposing to use.

If you keep the original varnish, rub it down with wet-and-dry to give it a key - 180-240 grit should be good enough. If you go finer you risk losing adhesion of the new varnish.

Epoxy sometimes develops a soapy residue or bloom, but a good rubbing with W&D paper will remove this and you can varnish straight over the top.

Use a good UV resistant flexible yacht varnish. I love International Schooner myself. And apply it with Jennybrushes (which you can buy on ebay, shameless plug).

Lots of thin coats are much better than a few thick ones, and will produce a much more durable finish. Allow each coat to dry thoroughly (more time needed as you build up coats), and lightly flat back between coats with 400 grit.

For stunning mirror finish:

- Flat back with 120 grit to the point where you cannot see any grain pits, which show up as shiny dots. You may need to build a few coats up first and then flat it back to this point. These coats fill in the grain pits above the surface level of the wood, and leave a smooth flat surface for topcoats
- subsequent coats are applied thinly, with 400 grit in between, and use a tack rag immediately before varnishing
- make sure that you time it correctly, with the right temperature. High humidity wrecks varnish (even under cover). 11 am is a good time to start varnishing, but on a good, dry day.
- If you are in a dusty workshop, wetting the floor first can keep the dust down

Best of luck!

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thanks for this - doesn't sound quite the mammoth amount of prep. work I'd imagined - though the rest will keep me busy.


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Roland has said the lot, including using flexible varnish. The polyurethane stuff is hard but brittle and can separate from the substrate.
I'd suggest giving the epoxy a bit of a scrub and a rinse.
Main thing is to keep on top of it by rubbing down and patching.
I should listen to my own advice.....spuddy

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I have sanded a clinker pram (mahogany) but decided to strip it down to wood as the varnish keeps flaking off and a half varnish half wood would look odd on re varnishing.
What I am not sure about though is whether to give it a couple of coats of epoxy then varnish on top. I have done this on plywood dinghies and it saves a lot of work but does the clinker need more freedom of movement than the epoxy would allow. The dinghy is traditionly built with copper rivets.
 
A boat builder mate of mine was staying with us this weekend and introduced us to G4 primer from Bondaglass. Swears by it... Also mentioned in MArch PBO for installing bulkheads
 
I know of G4 it is very easy to add many coats quickly and it likes damp conditions. For this project though I will keep to varnish as it is more flexible. I have since heard Epoxy is not a good idea as it may split the planks.
 
Agree with everyone. I stripped the varnish from the inside of my Heron and would think twice about doing it again. If the varnish there is in fair nick you could key it using Scotchbright. Different grades are available at automotive paint suppliers and it's so much easier than glass paper.
Varnish (traditional as well as polyurathene) takes well to epoxy. If the epoxy hasn't cured well (being wintery) you can scrub it with detergent and scotchbright to remove the waxy film that is sometimes left.
 
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