Boat U.S. - January 2008 - (Page 40) From the Files of DIY Boat Owner Magazine Surface Prep After consulting a few professionals who earn their living varnishing, one thing they all agree on is that proper preparation can make the difference between a mediocre and a high-quality varnish work. If you’ve no clue what the existing finish is, take a rag dampened in acetone and lay it on the surface for five to 10 minutes. A coating that softens is a one-part product; if the coating remains intact, it’s two-part. Again, read the application instructions for specifics. Provided an existing varnish is in good condition, wash the surface with a boat soap to remove any contamination. Sand with 220- to 320-grit wet or dry sandpaper and, once dry, wipe with a rag dampened with the recommended solvent (check the label). Some detailers scuff the surface with a Scotch-Brite pad (gray or red depending on the surface condition) and then varnish. Again, check the manufacturer’s guidelines. Any coating that shows signs of discoloration, lifting, cracking or peeling must be removed either completely or, if the damage is isolated, at the very least, do a spot repair. While you can use a cabinet scraper, sharpened to a chisel edge, to remove varnish in poor condition, you can expedite the process with chemical strippers and machine sanders. Scott Van Allen operates a varnishmaintenance business in Ft. Lauderdale, FL, and has been varnishing megayachts for 20 years. He prefers the one- and twopart urethane varnishes because of their short dry times and extreme hardness. “A traditional varnish that takes three or more hours to dry becomes a sticky landing place for dust and every passing mosquito,” says Van Allen. When stripping 300 feet (91m) of cap rail, he and his crew use a heat gun to soften the varnish and then scrape with a 2” (5cm) blade scraper. A light coating of paint stripper follows. This is scrubbed with scrapers and bronze wool brushes (the kind used to clean barbeque grills) to extract the varnish buried deep in the wood grain. Removable pieces, a flagstaff for example, are first scuffed with 60- or 80-grit sandpaper and then liberally coated in stripper and wrapped in cellophane or tin foil. “Apply about a 1/8” (3mm) thickness of paint stripper, cover with wrap and place the package in the shade so the solvent doesn’t dry, and it bubbles and cooks the varnish,” says Van Allen. Depending on thickness, it may take up to five hours to 40 BoatU.S. Magazine January 2008 remove seven coats of varnish. “Remove the wrap and wash the part with a hose. The wood now is clean and as flawless as new without having to sand out the gouge marks from scraping.” Once stripped, many woods need a good cleaning, especially if previously oiled. When I overlooked this important step by overcoating oiled wood with epoxy resin followed by multiple coats of polyurethane varnish, it all peeled off. I prefer to clean teak with a one-step teak cleaner and then lightly scrub the wood with a soft bristle brush rather than using the horribly toxic acid/alkaline cleaners. Don’t scrub hard or you’ll raise the grain. This might take several applications if the wood was oiled for many years. Besides an inventory of various scrapers and a file to keep them sharp, sanding blocks of different shapes, dual-action or orbital sanders and plenty of aluminum oxide sandpaper ranging from 60 to 320 grit, you’ll also need bronze wool, masking tape, tack cloths to remove surface residue, various size brushes, filters to strain the varnish, Scotch-Brite pads and a vacuum cleaner with an upholstery attachment. Dry-sand the wood to remove any imperfections caused by scraping. Begin with 80- or 120-grit paper, depending on the surface condition and the type of wood. Always sand with the grain and sand “by the numbers,” working up to the next finer sandpaper until you reach 180 or 220 grit, though some craftsmen sand further with finer grades. I rarely go above 180 grit when applying a two-part polyurethane varnish. (Unfortunately, all imperfections only become highly visible after applying the final varnish coat.) Always wear a dust mask when sanding. (The best mask for the job is 3M 9211.) A clean workspace helps to reduce the dust that always settles on cured varnish. Vacuum the wood and surrounding areas and wet down the floor or ground to prep for varnishing. Just before you varnish, solvent wipe the wood and finish off the prep by wiping with a tack cloth. Application 101 Gingerly stir, never shake, the can to reduce the amount of air introduced into the varnish. Pour a small quantity into another container and promptly reseal the can. Never varnish directly from the can. Besides adding dirt and other contaminates with every brush stroke, the solvents evaporate and the varnish thickens. All varnish products contain a solvent; some are more toxic than others. When in doubt, wear a respirator with a charcoal filter. If applying two-part varnishes, you’ll need a fresh-air supply system. Traditional varnishes are always thinned when applied over bare wood. Depending on the system and wood type, thinning ranges from 15% to 50%. When varnishing mahogany, Doug Theobalds, a former wooden boat craftsman and president of Epifanes North America, recommends thinning the first coat Above: Some of the tools in the author’s varnishing kit are bronze and synthetic wool pads, brushes and brush spinner, dust mask and respirator, power sanders, sanding blocks of various shapes and sizes, ScotchBrite pad scrapers, wet/dry sandpaper and tack cloths. Right: Brush or pat sandpaper clean using a 3M ScotchBrite Scuff Sponge to remove sanding residue and to improve cutting action. Photos by Jan Mundy
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