I've recently read several posts here on how spar urethane is superior to spar varnish, and I thought I'd do my own research on the subject. Admittedly, just because I Googled the terms for an hour doesn't make my findings any more credible than taking someone's word for it, but I thought I'd offer up a few contradictory posts from folks who seem to know what they are talking about in an effort to let the new TinBoat modder have another angle on the subject, and possibly do his own research.
What I learned in summary....
First, there is no regulation on what companies label their product. Therefore, the term "Spar Varnish" is not a stand alone recipe.
Second, spar varnish is superior to spar urethane in UV protection and flexibility. Spar urethane is better at repelling water. Each have trade off's. It seems that urethane would be the natural choice as repelling water is most important;however, urethane does not hold up to uv protection (for those who have wood exposed to the sun) and is not flexible (like most wood decks will be when exposed to extreme temp changes and walking/putting load bearing weights on them) and thus fail by cracking, which then allows immediate water penetration.
My hunch is that both could be the right solution for the right application in boats.
Here are a couple general discussions on it:
https://www.boatdesign.net/forums/wooden-boat-building-restoration/urethane-vs-varnish-13461.html
https://www.woodanswers.com/expertadvice_cat.asp?row_id=5602&part=full
quote "Spar Urethane" varnish should be avoided in any exterior application in which even moderate exposure to direct sunlight is likely.
https://hardwoodlumberandmore.com/Finishing/MarineVarnish.html
quote "It's best to stay awary from urethane ingredients"
https://www.refinishfurniture.com/email_spar_varnish_or_tung_oil.htm
quote "Alkyd spar varnishes are preferable to polyurethane spar varnishes because the alkyds tend to be less brittle than polys"
https://www.forums.woodnet.net/ubbt...al=&newertype=&olderval=&oldertype=&bodyprev=
I don't know that we have an authortative resource on the water sealer subject, but maybe this could be the "everything steelflex" posts for wood sealers.
What I learned in summary....
First, there is no regulation on what companies label their product. Therefore, the term "Spar Varnish" is not a stand alone recipe.
Second, spar varnish is superior to spar urethane in UV protection and flexibility. Spar urethane is better at repelling water. Each have trade off's. It seems that urethane would be the natural choice as repelling water is most important;however, urethane does not hold up to uv protection (for those who have wood exposed to the sun) and is not flexible (like most wood decks will be when exposed to extreme temp changes and walking/putting load bearing weights on them) and thus fail by cracking, which then allows immediate water penetration.
My hunch is that both could be the right solution for the right application in boats.
Here are a couple general discussions on it:
https://www.boatdesign.net/forums/wooden-boat-building-restoration/urethane-vs-varnish-13461.html
https://www.woodanswers.com/expertadvice_cat.asp?row_id=5602&part=full
quote "Spar Urethane" varnish should be avoided in any exterior application in which even moderate exposure to direct sunlight is likely.
https://hardwoodlumberandmore.com/Finishing/MarineVarnish.html
quote "It's best to stay awary from urethane ingredients"
https://www.refinishfurniture.com/email_spar_varnish_or_tung_oil.htm
quote "Alkyd spar varnishes are preferable to polyurethane spar varnishes because the alkyds tend to be less brittle than polys"
https://www.forums.woodnet.net/ubbt...al=&newertype=&olderval=&oldertype=&bodyprev=
I don't know that we have an authortative resource on the water sealer subject, but maybe this could be the "everything steelflex" posts for wood sealers.
