We’ve all seen them, the insanely pristine beautiful yachts with deeply gleaming varnished finishes that appear impervious to all that Mother Nature can throw its way. It’s pretty, no doubt about it, but before you let your heart make your boat finishing decisions for you, just remember, varnish takes a great deal of work to apply and upkeep must be done seasonally to maintain that gloss finish.
First, let’s look at a couple of definitions. Varnish is a transparent, hard, protective finish or film used in wood finishing. Classic traditional varnish has three basic components: drying oil, resin and a solvent. Drying oils are vegetable oils that dry in the air to form a solid film. Examples of drying oils are tung oil, linseed oil or walnut oil. Examples of Resins are amber (though it’s a little expensive, I would think), rosin (pine resin), or shellac.
(As a small interesting factoid, pure Shellac is a completely natural product that is scraped from the bark of trees where the female lac bug secretes it to form a tunnel-like tube as it traverses the branches of the tree. The number of lac bugs required to produce a single kilo (2.2 lbs) of shellac has been estimated at up to 300,000. This means huge numbers of insects on the host trees, up to 150 per square inch. Ick.)
The third component, solvent, is traditionally turpentine, but in more modern formulas solvents are more often mineral spirits like paint thinners.
To get back to the nautical applications, marine varnish, or ‘spar’ varnishes are formulated not necessarily for appearance (or UV resistance for that matter) but for flexibility. When sails are attached to spars, the spars flex under the cyclic loads, so if the protective finish is too hard it will crack and water will get in and there goes the protective qualities. Less severe but still important, decks flex as well (hell, let’s face it, the whole boat flexes as it goes through the water) so it’s not just for spars.
Varnish works much better applied in a number of thin coats rather than one or two heavy coats. According to John Vigor, the minimum number of coats of varnish required to get that deep gleaming professional look is 8 to 10. No that is not a misprint, 8 to 10 coats. Now bear in mind that before the varnish is applied, the surface on which it’s applied has to be completely dry, sanded, smoothed with bronze wool (as opposed to steel wool, which puts a gray tint to the wood), grain filled if necessary, and sealed. Only then can you apply your 10 coats of varnish. Between coats some people wet sand with insanely fine sandpaper. Before each varnish application, wipe the surface clean with a tack cloth dampened with a compatible thinner. Don’t work outside if it’s too hot, too cold or too damp, as that will cause the varnish to cloud. Don’t stir the varnish in the can or you’ll introduce bubbles. Swirl it gently in the can to mix it if you really feel it’s necessary. According to Vigor, mostly it isn’t, but for me the habit of stirring something before I dip my brush in it is just so strongly ingrained I don’t know if I could avoid it. One small bit of advice here, and this goes for paint as well as varnish, when a bug lands on your freshly applied surface (and they will, in spite of faith) do not knock them off immediately. I know that sounds weird, but stay with me. Let the finish dry and then knock them off, leaving the tiny tidbits of their teensy toes behind. If you try to get them off whilst the finish is still wet you’ll just end up buggering up the finish.
The previous paragraph illustrates why I’m not a great proponent of varnish. I don’t consider boats as furniture, because if they are actually used on the water the finish will inevitably get a little banged up, whether from coming into the dock, errant tools dropping on them or simply a clumsy misstep (and I tend to be clumsy at the worst times). But if you love making things pretty rather than spending time on the water, by all means, go for it.