new urethane over old

My canoe’s rails are finished with polyurethane (Minwax Helmsman Polyurethane Spar Varnish). The finish has weathered enough that I should refinish them somehow. I have been putting it off because I thought that I needed to sand off all the old varnish and start with bare wood. But another member of my club, with lots of experience with wood finishing and canoes, tells me I can just sand the peeling areas, then add varnish to the bare parts.

Any opinions? I don’t care if it looks a little funny, but I do want to protect the wood well.

I saw on another thread that two people prefer a Varathane polyurethane spar to the Minwax. Are the two finishes compatible in this partial-refinishing plan?

While I’m asking: do things get worse if I put an oil finish on the bare wood, rather than more polyurethane? I figure that’s less likely to be compatible, but I prefer an oil finish, so maybe I can be lazy and slowly convert the varnish to oil. I suspect the oil will make the varnished areas sticky, but will otherwise be okay. The oil in question is my eight-year-old can of Watco, if that is still usable.

Oh, always another question: Should I remove the rails and varnish (or oil?) the screw holes and the insides of the rails? Both areas have blackened a little, presumably from lack of protection from water. I have never removed gunwales and have no idea how likely I am to mess it up. I have access to basic tools like drills, nothing fancy.

The boat is a Placid Boatworks RapidFire, by the way. I have had it six years and have done very little maintenance to the rails. It has been stored exclusively inside, but it is used in brackish water (rinsed off with freshwater after most trips), and it is exposed to New York City’s temperature and humidity.


redoing bright finish
I generally use varnish instead of polyurethane but I think the same principles apply. I don’t find it necessary to take the finish down to the bare wood unless it is really bad. Any areas in which the wood has greyed or otherwise discolored of course have to be taken down to clean wood, and any peeling or raised finish needs to go, but areas in which the finish is still intact I would just lightly sand with something like 120 grit paper to slightly rough the surface before reapplying polyurethane.

I haven’t tried it, but I don’t think I would apply oil to wood partially finished with polyurethane. I doubt that it would hurt anything but I am doubtful it would look good.

If you really want to go from a bright polyurethane finish to an oil finish I would probably go ahead and take the gunwales off. It is a lot easier to sand down to bare wood without scratching up the hull that way and you can seal the hidden wood of the inwales and outwales at the same time. You have to be careful not to accidentally break those long, narrow rails when they are off the boat, though.

I haven’t generally had trouble getting wood gunwale screws out except on boats such as Bells in which a couple of long screws near the stems go all the way through the outwale, the inwale, and into the deck plate. As I remember, the deck plates on the Rapidfire sit atop the inwales so you shouldn’t have that problem.

If I remove the gunwales I now generally sand the inside of the outwales and the outside of the inwales and apply epoxy as a wood sealer. I think it provides better protection from wetness and holds up better than anything else. If you don’t have any I would use polyurethane or varnish on that surface even if you are oiling the part that shows as I think it is more durable.

PU over PU should be fine.

– Last Updated: Nov-08-12 9:56 PM EST –

I'd stick with the Helmsman, but any polyurethane will work.

Scuff-sand with 220, wipe down with paint thinner, and apply 2-4 coats with a light sanding between coats to knock down any raised fuzz or stuck particles. Once it's all fully cured, you can rub it out with #0000 steel wool if you prefer a satin sheen, but gloss protects better

Go ahead and pull the rails and revarnish all sides. It's recommended by many.

Stripping what's left of the varnish completely is probably best before switching to oil.

If you use Varathane…
…make sure you DO NOT use their water-based outdoor varnish. It is pure, unadulterated junk. I had a very bad experience with it when I used it to refinish my wooden kayak paddle. After paddling for a few minutes it started turning white and peeling off! It looked just the way your skin looks when a popped blister starts to peel off. I could not believe my eyes.

Later a friend used it to varnish an entire cedar strip canoe. Guess what happened…

No steelwool…
any steelwool particales will rust when they come in contact with water in a marine enviorment, no matter how well you vaccuum.

Use a fine sandpaper or a sanding sponge to sand between coats, but leave the steelwool for interior refinishing projects.


Maybe true for bare open-grain wood
like oak or even ash, but for rubbing out varnish, there’s really little risk of leaving broken-off fibers. Bronze wool is an alternative or a Scotchbrite pad, but the grit grades in nylon pads are uneven and I’ve found too agressive for rubbing out finish. Graded pumice or rottenstone works well, too, but they’re cumbersome to use on small shapes like canoe trim.

If Urethane, Refinish with Urethane
If spar varnish, refinish with spar varnish. If different than original finish, take it down to bare wood before refinishing with something different.

Regarding Urethane on canoe paddle shafts, I find it a wee bit more slippery than spar varnish on my hands when racing though. For general recreational paddling, it doesn’t matter. On gunnels, it’s great.

I refinished my gunnels every year
with Spar Urethane. Sanded them with fine sandpaper, cleaned them and reapplied. Never sanded to bare wood.

Me Too
Unless, the original finish was spar varnish and I’m re-doing with Spar Urethane.