Boat U.S. - January 2008 - (Page 39) From the Files of DIY Boat Owner Magazine An ultraviolet stabilizer is the single component that most directly impacts longterm performance. Without the use of adequate stabilizers, the varnish (or any coating for that matter) absorbs the UV energy. This leads to a dramatic loss of gloss, film cracking and yellowing. Oxygen reacting with the coating now oxidizes the surface, causing the varnish to fade and become cloudy. Most external-use marine varnishes contain a UV absorber that diffuses and disperses UV to prevent coating damage. Some varnishes also contain a surface stabilizer to repair UV damage and antioxidants to combat surface oxidation. Yellow is sometimes added to a varnish as a UV inhibitor and gives the finish an amber tone. Climactic and environmental conditions all affect the longevity of a varnish, assuming the varnish was properly applied. As a varnish oxidizes, it becomes more brittle and prone to cracking and crazing. Varnish that is continually immersed in water tends to blister and delaminate. Salt crystals, acid rain and other contaminants magnify sunlight’s intensity and cut through the coating. Spilt fuels, alcoholic beverages and even sunscreens can damage a varnished finish. Photo by Scott Van Allen Above: To remove oil from teak prior to varnishing, clean with a one-part teak cleaner and lightly agitate the surface with a soft bristle brush. Right: Hold the heat gun at an angle and scrape off the loose varnish. Keep moving the gun so it doesn’t scorch the gelcoat or wood. Product Choices Walk into any well-stocked marine store and you’ll find an array of products. What do you choose? Spar varnishes are phenolic or alkyd resins combined with tung oil to produce a varnish with good water resistance, adequate hardness, exceptional flexibility and good grease and UV resistance. Examples of spar varnishes include Awlspar, Epifanes Clear Varnish, Interlux Original and Schooner, Petit Bak-V-Spar, Captain’s and Flagship, Sikkens Rubbol, System Three Spar Urethane and West Marine Admiral’s. All are one-part coatings, known for their ease of application, and some are compatible with epoxy resin. Hard and durable, polyurethane varnishes exhibit the finest abrasion, chemical and water resistance but are the least flexible. A tiny crack or nick can allow water to creep under the film, raising the grain and peeling the coating. Their hard finish can be buffed or polished to produce the finest smoothness and gloss. Varnish purists might consider their high-gloss, “plastic” wood look a detriment. One-part polyurethanes (e.g., Detco Crystal, Interlux Goldspar 95, Sikkens PU Clearcoat) require less care and are more easily applied than the two-part coatings (e.g., Interlux Perfection, Epifanes Polyurethane Clear Gloss). Interlux Perfection combines both UV absorbers and antioxidants to deliver UV protection up to four times longer than traditional varnishes. As expected, urethanes are the most expensive of the varnishes, as much as three times more than a spar varnish. Fast-dry finishes contain a modifying resin to produce a varnish with remarkably fast drying times. Toluene or naphtha, listed on the label, identifies a coating as a fastdrying finish. Fast-dry times mean less dust and fewer bugs to get stuck in the finish as it cures. Bristol Finish is a two-part acrylic urethane coating with a one- to 24-hour recoating time without sanding between coats. In one day, you can potentially apply eight coats or more. A fast buildup is especially practical for early spring and late fall varnishing or anytime there is a diminished weather window. Some specialty varnishes are applied without the hassle of sanding between coats. Epifanes Wood Finish Gloss is a blend of phenolic-modified resin and tung oil that builds up coats quickly without sanding if recoated within 72 hours. Five coats of Wood Finish are equivalent to seven coats of varnish. Epifanes Rapidclear, a one-part modified alkyd and urethane resin finish, goes on very thin so it doesn’t fill the grain like a varnish but requires only five coats over bare wood. It’s not necessary to sand, provided moisture or dust isn’t trapped between coats. Most of these products are compatible with oil-based penetrating wood stains, many can be applied over epoxy-resin- coated wood and, with the proper preparation, most bond well to teak. Generally, traditional spar varnishes take longer to dry than the urethanes and require a buildup of eight or more coats. Two-part polyurethane varnishes are dry to the touch in one hour or so, giving bugs and dust little time to adhere. They are re-coatable in three or four hours and, as they only require five or fewer coats for the same level of protection, the varnishing is completed in a weekend. Rarely is there a compatibility problem between one-part varnishes. Problems occur when overcoating a two-part finish because it acts like paint remover; exceptions include one-part Bristol Finish and Detco Crystal. As with all coatings, read the application instructions carefully and apply to a test area before starting a big project. Alternative synthetic varnish look-alikes (e.g., Cetol, Amazon Teak Lustre) are also popular. They are an easy-to-apply option, especially over oily woods like teak, with good durability and a passing-grade finish. Cetol is an alkyd resin formulation containing synthetic transparent iron oxide pigments that protect the wood against UV absorption. It’s these pigments that turn wood a “golden” hue. Cetol is very easy to maintain. When the coating begins to lose gloss, simply scuff it up with a Scotch-Brite pad, rinse with a vinegar/water solution and apply a few fresh coats. Amazon’s Teak Lustre is a one-part, water-based acrylic coating that can be applied over many teak oils. It’s a quick-drying finish, ready in 45 minutes or less for sanding between coats, which allows for the recommended three coats to be applied in an afternoon. 39 BoatU.S. Magazine January 2008
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