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Urethane verse Varnish... Help

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Forum topic by Blackfin29 posted 09-20-2019 12:26 AM 335 views 0 times favorited 14 replies Add to Favorites Watch
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Blackfin29

125 posts in 682 days


09-20-2019 12:26 AM

Can someone explain the difference when talking about “Exterior” types???

I’m considering an oil based, exterior urethane… Once I strip the “Spar” varnish from a teak boat dinette table.

How does an exterior Urethane differ from a spar varnish??


14 replies so far

View wildwoodbybrianjohns's profile

wildwoodbybrianjohns

333 posts in 60 days


#1 posted 09-20-2019 06:09 AM

I am sure youre gonna get all kinds of replies to your query, my 2cents is:

To me, spar varnish is Urethane (poly) cut with something, for example, when I do exterior wood that has to hold up to spanish sun and fall rains, I use a mix of marine varnish (glossy) linseed oil and mineral spirits in equal parts, and I am not all perfect about the mix, I just eyeball it, usually more MS in the first coat. And I call that spar varnish.

-- Wildwood by Brian Johns: It is wiser to find out, than to suppose (S. Clemens)

View Fred Hargis's profile

Fred Hargis

5760 posts in 3006 days


#2 posted 09-20-2019 10:32 AM

I have no idea what an “exterior urethane” is but I’d guess it has UV inhibitors added. Varnish is a compound formed by cooking oil and a resin under high temps and pressure. Spar varnish is actually a “long oil” formula that goes into the cooker to make the varnish (what folks usually refer to as “polyurethane” or “urethane” or “poly” is actually varnish). Long oil simply means there is more oil in the mix, creating a softer finish that moves a little with the wood. The problem with all of this is that urethane resins don’t do well in high UV environments, that’s why the true marine spar varnishes use other resins in the formula. They also use considerable amounts of UV absorbents. I read a review by Flexner where he tested some box store spar varnishes…..The Helmsman did so poorly in the sun he speculated it didn’t have any UV absorbents, even though the can is labeled that it does.

-- Our village hasn't lost it's idiot, he was elected to congress.

View John Smith's profile

John Smith

2017 posts in 676 days


#3 posted 09-20-2019 12:00 PM

after you refinish the table, will it be used inside the house, outside on a deck
or on your boat ??

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-- I am a painter. That's what I do. I paint things --

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John Smith

2017 posts in 676 days


#4 posted 09-20-2019 04:42 PM

this is a rather long read, but, covers some of the differences between the two.

Varnish vs Polyurethane

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-- I am a painter. That's what I do. I paint things --

View Blackfin29's profile

Blackfin29

125 posts in 682 days


#5 posted 09-21-2019 01:55 PM

Thank you to all that commented!!

I’m beginning to think the ONLY way to see if you like a product is to try it, and see if it lasts… Test it out.

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Blackfin29

125 posts in 682 days


#6 posted 09-21-2019 03:34 PM

I have one other question…..

Are GLOSS finishes typically thicker, more viscous, than Satin or Semi-Gloss??

View Fred Hargis's profile

Fred Hargis

5760 posts in 3006 days


#7 posted 09-21-2019 03:35 PM

It’s a common practice (prove it to yourself) and worthwhile, IMHO. Combine the misconceptions fed to us by the manufacturers and a wide range of results we collectively achieve with all the various finishes it’s easy to be misled. I do suggest you get a book about finishes, the best (again, IMHO) is the one by Bob Flexner. Easy to read and answers almost any question about finishing you would have….plus his advice is proven. Another one would be the one by Jeff Jewitt, very much the same info but arranged in a different manner.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Rich's profile

Rich

5001 posts in 1103 days


#8 posted 09-21-2019 04:01 PM


I have one other question…..

Are GLOSS finishes typically thicker, more viscous, than Satin or Semi-Gloss??

- Blackfin29

No. They are the same product. Satin and semi-gloss simply have flatteners added to reduce the sheen.

View wildwoodbybrianjohns's profile

wildwoodbybrianjohns

333 posts in 60 days


#9 posted 09-21-2019 04:17 PM

Like Rich said. Gloss accentuates whats underneath, satin hides it.

-- Wildwood by Brian Johns: It is wiser to find out, than to suppose (S. Clemens)

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Rich

5001 posts in 1103 days


#10 posted 09-21-2019 04:34 PM

Like Rich said. Gloss accentuates whats underneath, satin hides it.

- wildwoodbybrianjohns

I take exception to that, but that’s another topic.

Also, I should have added that different sheens of the same product do not vary in viscosity. Obviously, some products are more viscous than others.

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wildwoodbybrianjohns

333 posts in 60 days


#11 posted 09-21-2019 08:16 PM

Well, satin urethanes have more flattening paste to take the luster out, so you end up with less sheen (as you said). Glossy urenthanes have less of this flattening paste and thus a far shinier result. Therefore, whatever is under a glossy finish is going to be pronounced; and whatever is under a satin finish will be somewhat obscured, dependent upon the level of sheen. Such is why, when using a gloss finish, it is much more critical to prep the surface well, whether its metal, wood, sheetrock, or plaster, or whatever, because the gloss finish will accentuate what lies under it! To the other end of the spectrum, there is a matte finish, which hides deformities the best of all because of the lack of sheen. This is all common knowledge to any painter worth his weight, so I cant fathom why anyone would take exception???

Apologies if there was a misunderstanding, my post was a compound statement: like he said + what I said.
It wasnt paraphrasing or parroting.

-- Wildwood by Brian Johns: It is wiser to find out, than to suppose (S. Clemens)

View farmfromkansas's profile

farmfromkansas

125 posts in 127 days


#12 posted 09-21-2019 08:17 PM

When in shop class years ago, the teacher said the gloss is the most durable finish, and that satin has basically a product like dust to make the finish lose the gloss, which makes it lose some of it’s strength. So I just use gloss, and it seems to lose some of it’s sheen over time.

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Rich

5001 posts in 1103 days


#13 posted 09-21-2019 08:43 PM


Apologies if there was a misunderstanding, my post was a compound statement: like he said + what I said.
It wasnt paraphrasing or parroting.

- wildwoodbybrianjohns

It’s all good. Discussions pop up about whether it’s better to do gloss undercoats and finish with a satin if you want that sheen. The argument is you get better clarity. I suppose, but honestly I’ve done it both ways and don’t see a difference.

I will say that for a tabletop, when I want a perfect finish, I do ten or twelve coats of gloss lacquer and then rub it back to the sheen I’m looking for. I like wet sanding with Mirka Abralon pads on my 6” dual action sander/polisher.

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Rich

5001 posts in 1103 days


#14 posted 09-21-2019 08:54 PM


When in shop class years ago, the teacher said the gloss is the most durable finish, and that satin has basically a product like dust to make the finish lose the gloss, which makes it lose some of it s strength. So I just use gloss, and it seems to lose some of it s sheen over time.

- farmfromkansas

I’m afraid the teacher was mistaken. The flatting material is typically silica and has no effect on the durability. In fact, gloss finishes will show scratches and scuff marks far more than a lower sheen.

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