Varnish and various wood oils have been the traditional transparent wood finishes on boats for hundreds of years. Their lack of pigment allows the beauty of the wood grain to show through, while protecting the wood from the ravages of sunlight, saltwater, dirt, and abrasion. The finish achieved after careful application can vary from practically invisible protection for interior and exterior wood, to a glossy fine-furniture coat in which you can see your reflection.
In addition to wood oils and varnish, there is a new category of wood finishes gaining popularity in the marine market. To say "gaining popularity" is a massive understatement; all you have to do is ask about Sikkens Cetol or WoodPro Plus on an Internet forum, and you'll have 50 responses from around the globe debating its properties, comparing it to other finishes, and explaining EXACTLY how to apply it.
Assuming you want to protect and beautify your boat's exterior wood, how do you select among the incredible (dare we say baffling?) variety of finishes? Knowing full well that this is as big a minefield as debating the benefits of power vs. sail, we nonetheless courageously offer the following observations:
Oils generally maintain the original look and texture of the wood more than the other finishes because they penetrate deeply into the wood fibers and do not create as much of a surface coating. Oils are available in colors ranging from water clear to gold to dark brown. As with any wood finish, multiple coats generally result in a more uniform finish and greater longevity. We find oil to be the easiest to apply, since surface blemishes are not as apparent in the final outcome. This does not mean, however, that slapping four coats of oil on dirty teak will produce a Bristol finish. You’ll also find that oil’s thin consistency makes masking to protect surrounding gelcoat and painted surfaces almost as important with oil as with varnish. Clean, sanded teak with several coats of oil can provide 3-6 months of beauty and protection.
Varnish is a complicated finish consisting of oil, solvents and thinners, resins, dryers and additives. By varying the proportions of the components and by adding UV inhibitors and other secret ingredients, manufacturers create varnishes with widely varying characteristics. Varnish can have a gloss or matte appearance, can be formulated to be extremely hard for walked-on surfaces and can vary in color. The two most common types of varnishes are natural resin varnishes such as tung oil and oil-modified polyurethane varnishes. Natural tung oil varnishes are excellent for interior or exterior use and offer the classic golden look. Oil-modified polyurethanes tend to be more clear, allowing the color of the wood to shine through. Wood moves, since it is a formerly living thing, expanding and contracting with even subtle changes in temperature and humidity. Premium varnishes cope with this dimensionally unstable material using high quality oils and resins and higher percentages of solid ingredients, providing a longer lasting, more flexible finish with a higher gloss. Mil thickness is everything. A good base, regularly and diligently maintained, will give the ultimate in appearance, longevity and protection. Despite the initial effort (up to ten coats are common) nothing looks better than exterior wood finished with gloss varnish.
Synthetic Wood Finishes
These satin coatings gained popularity with cruisers in the tropics looking for UV-resistant, low-maintenance brightwork. Formulated for ease and speed, these finishes have remarkable durability for exterior use, are easy to apply and look relatively good. We say relatively good because some of these products, like Cetol Marine, tend to have a pigmented appearance, with an orangish brown cast. We formulated our WoodPro Plus with no pigment so the wood’s natural appearance is preserved. Full gloss and depth vs. convenience is the tradeoff with these finishes, but simplicity and labor savings can more than compensate. Ease of application is similar to teak oil, where you can apply it directly over sanded, clean wood. Rapid drying and no need for sanding are two of the many advantages of WoodPro Plus. Cetol comes in four varieties, with the Natural providing a more golden color resembling the real look of raw teak. Overcoat any of the other Cetol finishes with the Gloss for a shiny exterior finish. As with all clear finishes, masking surrounding areas is highly recommended.