Boat U.S. - January 2008 - (Page 38) From the Files of DIY Boat Owner Magazine Different Strokes The brightwork professionals all agree that preparation and the right products are essential to a successful, enduring and beautiful varnish job. an owner of a wooden boat, I’ve had my share of varnishing mishaps. Every spring would find me in the boatyard scraping, sanding and varnishing. Somehow, I never had enough time to apply the buildup of coats needed to protect the varnish from the sun’s rays but I always had to make time to scrape away the peeling, cracking varnish of last year’s effort. My obsession for the well-varnished look drove me in my search for the Holy Grail of a quick-and-easy finish, a quest compromised by my letting go of my goal of the “royal” finish that some can achieve with a magic formula that perennially eluded me. Ask four boat detailers what varnish they use and how they apply it and you’ll get four different answers. Knowing a little about varnish chemistry will help select one that’s right for your project. As Photo by Jan Mundy What’s Varnish? Varnishes are generally a concoction of oil, solvents and thinners, resins, dryers and additives. By varying these ingredients and/or their proportions in the mix and adding ultraviolet (UV) inhibitors to protect the wood from the harmful effects of the sun and other proprietary ingredients, each varnish achieves its own unique “personality.” Most are brushable, some are only sprayable, some give a high gloss and others a matte finish. They can vary in depth of color. Which varnish “personality” is best for you? Chemically combining a resin with oil produces a liquid varnish that cures to a solid film after application. Highquality marine varnishes use Chinese tung oil derived from trees. Lesser-quality varnishes use linseed, soybean or 38 other oil. Oil improves penetration into the wood and provides resistance to cracking and crazing. The ratio of oil to resin determines the flexibility of the coating, drying times and application method. Varnishes containing 45% to 60% oil form the basis of all marine varieties. Hard resins used in varnishes are generally derived from tree stumps or are processed from crude oil. Phenolic resins, derived from crude oil, are used primarily in varnishes requiring a faster dry and harder finish for maximum water resistance. Of the oil-modified polyurethane resins, there are two groups: aliphatic modified polyurethane resins and aromatic polyurethane resins. Both offer excellent abrasion and chemical resistance. The aromatics are more popular but the aliphatics provide better color, gloss and clarity. Poly-Flow 4000 is an aliphatic resin, which is unique to Interlux Goldspar 95 varnish. Solvents increase the leveling characteristics of a varnish. By maintaining a wet edge, the varnish is applied without any trace of brush marks from overlapping new areas. Driers accelerate the dry times and the hardness of the coating. The blend of driers can impact the clarity, color, the actual rate of dryness and the stability of the product. Additives are the newest components added to varnish. An anti-skinning agent allows the varnish to maintain a wet surface upon exposure to oxygen. Since varnishes have high resin content, they tend to develop a surface skin once opened. Flattening agents, used for interior varnishes, achieve a rubbed effect. BoatU.S. Magazine January 2008
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