gloss vs. semi-gloss
You can literally apply any varnish over another varnish as long as the base is clean, dry and oil and wax-free.
As for the difference between interior and exterior (which includes spar or marine) varnishes, there are several differences in them. As Glen noted, the spar varnishes have UV inhibitors, which are needed any time you want to protect a finish from UV sunlight damage. In the case of strippers, these inhibitors protect both the varnish itself as well as the epoxy underneath which is very susceptible to UV damage if left unprotected. The biggest structural difference between interior and spar varnishes is that spar varnishes have a higher percentage of oil, by volume, than interior varnishes. This is called a long oil varnish. This results in a finish that is much more flexible than the interior varnish, which is needed to allow the varnish to stretch and compress with wood movement caused both by external forces, as well as seasonal/temperature changes. It also helps in keeping the varnish from drying out. Almost all spar varnishes also use tung oil as the base oil rather than linseed oil which is the base in most interior varnishes. Tung oil is not only harder and tougher, relatively speaking, then linseed oil, it also holds up to weathering, such as sunlight, heat, water, freezing, etc., better than linseed oil. Cosmetically, tung oil also doesn't darken over time like linseed oil does.
So technically you can apply any varnish on a hull, but the spar varnishes will last longer and the UV inhibitors protect the epoxy. I would not put a polyurethane varnish on a hull however. If you can't find a low luster in Epiphane's line, or anyone else's for that matter, you can always apply the base coats in gloss, then add a semi-gloss or satin coat of a cheaper varnish like McClosky, Minwax, etc. The main difference in cheap and expensive spar varnishes is the amount of UV inhibitor, which is an expensive additive.
As for the difference between interior and exterior (which includes spar or marine) varnishes, there are several differences in them. As Glen noted, the spar varnishes have UV inhibitors, which are needed any time you want to protect a finish from UV sunlight damage. In the case of strippers, these inhibitors protect both the varnish itself as well as the epoxy underneath which is very susceptible to UV damage if left unprotected. The biggest structural difference between interior and spar varnishes is that spar varnishes have a higher percentage of oil, by volume, than interior varnishes. This is called a long oil varnish. This results in a finish that is much more flexible than the interior varnish, which is needed to allow the varnish to stretch and compress with wood movement caused both by external forces, as well as seasonal/temperature changes. It also helps in keeping the varnish from drying out. Almost all spar varnishes also use tung oil as the base oil rather than linseed oil which is the base in most interior varnishes. Tung oil is not only harder and tougher, relatively speaking, then linseed oil, it also holds up to weathering, such as sunlight, heat, water, freezing, etc., better than linseed oil. Cosmetically, tung oil also doesn't darken over time like linseed oil does.
So technically you can apply any varnish on a hull, but the spar varnishes will last longer and the UV inhibitors protect the epoxy. I would not put a polyurethane varnish on a hull however. If you can't find a low luster in Epiphane's line, or anyone else's for that matter, you can always apply the base coats in gloss, then add a semi-gloss or satin coat of a cheaper varnish like McClosky, Minwax, etc. The main difference in cheap and expensive spar varnishes is the amount of UV inhibitor, which is an expensive additive.
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Chuck in Pa
- Posts: 17
- Joined: Tue May 11, 2004 4:51 pm
- Location: Philadelphia, Pennsylvania
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At the 2004 Meet at the Beach, there was a hybrid kayak with a kevlar hull and a woodstrip deck that had a matte or semigloss finish.
I was really amazed at how well it turned out. It look far more regal than many of the other boats, though some of this may have been attributed to it's excellent craftsmanship.
I don't think it is for every boat, but for understated, but very well built boats it can really bring out the workmanship.
I think it would bring out a lot of flaws though, as well as being slightly less UV resisitant. Matte varnish reflects less light, and thus abosrbs more.
I'll stop talking now.
-Chuck in Pa
I was really amazed at how well it turned out. It look far more regal than many of the other boats, though some of this may have been attributed to it's excellent craftsmanship.
I don't think it is for every boat, but for understated, but very well built boats it can really bring out the workmanship.
I think it would bring out a lot of flaws though, as well as being slightly less UV resisitant. Matte varnish reflects less light, and thus abosrbs more.
I'll stop talking now.
-Chuck in Pa
Thanks for all the input guys. The Epifanes product that Glen refers to is a synthetic wood finish available in gloss and matte. From what I read in the West Marine Advisor these synthetics were developed for use over tropical hardwoods because of the oil content of the wood. The really great feature about the Epifanes finish is no sanding required between coats. I may have to give this product a try. If I don't like the matte finish I guess I could always go over it with gloss.