Varnishing with urethane

jon hansen · May 16, 2020

i wish i knew more myself. up here on the lakes i'm an epifanes guy. my cousin, a ft laurderdale sailor and refinisher and airplane refinisher is a 'Captain's' man. different climates.
that said, i am going to change to interlux's #96 schooner varnish after watching the results on my buds boat.
it's also recommended by Rebecca j Wittman in her book Brightwork the art of finishing wood
fresh water up north, vs, where you are capta. i like tradition

dLj · May 16, 2020

As always, it depends... There are mono polyurethanes and two component polyurethanes. You can use varnish with mono component polyurethanes, but I believe you have problems if you are using two component polyurethanes. I prefer to use epoxy (specifically west system epoxy) as a base coat and then use a varnish on top. I find that to be a beautiful and durable coating system, easy to maintain over time.

dj

dlochner · May 16, 2020

Interesting question. If the polyurethane is prepped properly for the final varnish coat(s) I don't see why it won't adhere. However, traditional varnishes and spar varnishes are a bit more flexible than polyurethane to accommodate expansion and contraction of the wood from sunlight.

Might be worth an experiment on a small section of the brightwork.

All U Get · May 16, 2020

I agree with Dave, let me offer my boat as a good practice area.

jaysweet · May 16, 2020

I'm mostly ignorant on the subject, so let me ask: how is the term "varnish" not just a generic term for "clear finish that you apply to something"? From Wikipedia:

"Varnish is a clear transparent hard protective finish or film. [...] The term "varnish" refers to the finished appearance of the product. It is not a term for any single or specific chemical composition or formula."

I just finished a new panel for our interior using Minwax Helmsman Spar Urethane. Is there any way to really distinguish whether a particular product is a urethane, a polyurethane, or a "spar varnish"? I'm really not telling: I'm asking.

DougM · May 17, 2020

Fortunately I don’t have a lot of parts on my boat needing varnish.
I became familiar with Epifanes when volunteering on tall ships locally. I was taught after initial prep work (a lot of sanding) to apply ”several” coats of clear Epifanes using a scotchbrite pad between coats to scuff up the surface, followed by tack cloth, the wiping down with mineral spirits, and then use a final coat of matte finish, the thinking being that the matte finish would somewhat inhibit UV breakdown.

We had the advantage of working indoors and controlled conditions during the winter which had a lot to do with obtaining a really consistent finish. The better the quality of the varnish brush itself, the better the finish.
Between coats, rather than completely cleaning out brushes, after wiping excess varnish out, let them soak in container of motor oil.

dlochner · May 17, 2020

jaysweet said:
I'm mostly ignorant on the subject, so let me ask: how is the term "varnish" not just a generic term for "clear finish that you apply to something"? From Wikipedia:

"Varnish is a clear transparent hard protective finish or film. [...] The term "varnish" refers to the finished appearance of the product. It is not a term for any single or specific chemical composition or formula."

I just finished a new panel for our interior using Minwax Helmsman Spar Urethane. Is there any way to really distinguish whether a particular product is a urethane, a polyurethane, or a "spar varnish"? I'm really not telling: I'm asking.

Varnish is a pretty generic term these days. Read the ingredient label to see the difference. Traditional varnishes are based on Tung oil and phenolic resins, polyurethane resins are based on well, polyurethane. Every company has different formulations but most, if not all, are based on either polyurethane resin or phenolic resins. For exterior work I prefer Epifanes Woodfinish Gloss. It develops a rich clear gloss that lasts a long time. It also can be over coated within 72 hours without sanding.