PS Advisor: 07/15/04
Can you give me a recommendation for varnishing my inflatable's floorboards and transom? I have used Captain's varnish by Pettit and Schooner varnish by Interlux in the past, but they seem to indicate that these are not for below the waterline. Should I be looking at something else?
As Chuck Hawley, the very capable editor of the West Marine catalog, once wrote in West Advisor, "If you want to bring the entire Internet to its overloaded knees, post a strongly-worded message about varnish."
Practical Sailor has been testing varnish for years and will not flinch from this challenge. We know not where Mr. Kearney got the impression that either of the varnishes he named are not for use below the waterline. Varnish is, first and foremost, a sealer.
Varnish used to be relatively simple stuff derived by squeezing resins out of various plants and adding a drying oil derived from the nuts of tung trees. Add a chemical to speed the drying, flatten it, and you had a tough, shiny, waterproof coating.
Nowadays, varnish is a fancy formulation that defies description by anyone other than chemists working in a very specialized field. Most varnish these days claims to be polyurethane and who’s to dispute that? "Poly" means "many" or “something made of this.” So, whether they foam it (Styrofoam), roll it (Saranwrap), or pour it, it’s all plastic.
On most cans, the contents list includes "alkyds," which are fake resins made by heating hydroxy alcohol with polybasic acids or their anhydrides—most of them derived from petroleum. (Those who market what the chemists do changed "fake" to "synthetic," but didn’t go as far as the pearl people with their fancy-sounding French term "faux.")
To these modern formulations, the manufacturers of varnish add chemicals that make it shiny or dull, thick or thin, more or less viscous, and more or less crystal clear. (PS once tested the color-free nature of a dozen varnishes by simply applying a brush-wide strip of each to a white shirtboard; the differences were considerable.)
They also add UV protection, and the latest trick in this regard is nothing more than finely ground iron that bounces around the sun's rays and absorbs its energy; the particles actually heat up a bit.
Mr. Kearney’s problem of getting varnish to adhere to his inflatable's floorboards is not uncommon. Some experts say that getting varnish to take a bulldog bite on wood can be encouraged by thinning the first coat (on raw wood). We've tried it both ways and could not establish that thinning helps. We also do not believe that eight thin coats are better than three or four heavy coats. On most surfaces, we apply vanish heavily, just short of sagging, spread it quickly and leave it to flatten.
Unless subjected to considerable wear or abrasion, varnish fails because water gets under the skin and deteriorates the wood as well as loosening the bond between the wood and varnish. This happens mostly in cracks, worn edges, deep scratches, knicks and gouges. That's why, when depending on varnish to protect the wood, it's vital to completely encapsulate the wood in varnish (unless you're testing varnishes as we are).
Reader Kearney's floorboards, being of plywood, pose an extra hazard because most plywood contains voids that retain moisture. Heating and cooling of these moisture spots produce expansion and contraction that can crack the plastic skin.
If we were to seek the best possible treatment, we’d sand the floorboards and transom and let them cook in the sun for several very hot, dry days. We'd then apply three or four coats of any marine varnish (paying attention to edges), sanding lightly between each coat.
So which varnish should you use? There are lots of good ones (those are principally the expensive ones), but in PS's current long-term test of varnish and other teak coatings (the initial report was published in the Nov. 15, 2003 issue), we’re using the three varnishes that topped a dozen or so others in a prior varnish test. The three are Epifanes Wood Finish Gloss, Pettit Hi-Build and West Marine’s Skipper's.
If Mr. Kearney wants better protection for his floorboards, he could opt to use a good marine enamel, which because it's thoroughly pigmented, offers superior UV resistance.