Popular Woodworking 2000-02 № 113, страница 62
contains "petroleum distillate." Real tung oil doesn't contain petroleum distillate. Wiping varnish is also sold as Waterlox, Seal-a-Cell, Val-Oil and Profin. Oil-based polyurethane and wiping varnish are easier to use than water-based finishes, which dry very fast, raise the grain and are difficult to use in combination with stains. Oil-based polyurethane provides excellent durability with only two or three applications. Wiping varnish goes on with reduced brush marking and fewer dust nibs but requires many more applications to achieve the same durability. Polyurethane is best for surfaces that get a lot of wear. Wiping vanish is best when you want a thinner, more flawless finish. Applying Polyurethane Apply polyurethane using a bristle or foam brush about 2" wide. Foam works well and eliminates the chore of cleaning, because the brushes are cheap and thus disposable. You can apply the first coat full strength or thinned up to half with paint thinner, making, in effect, a wiping varnish. (Use a separate can or jar.) Thinning leaves less actual finish on the wood so the finish dries hard faster and is thus easier to sand sooner. Always sand the first coat of finish smooth to the touch after it has cured (usually overnight in a warm room) using 280-grit or finer sandpaper. Remove the dust with a tack rag (a sticky cloth you can buy at paint stores) or a vacuum and apply a second coat full strength. Brush the polyurethane just like brushing paint. If there are bubbles, brush back over the finish lightly to make them pop out. Brush with the grain of the wood when possible. On flat horizontal surfaces such as tabletops, spread the finish onto the wood working from side to side (with the grain) and front to back. Stretch out the finish as thin as possible. After every 6" to 12" of surface covered from edge to edge, line up the brush strokes. Do this by lightly bringing the brush down onto the surface near one edge in an airplane-like landing and moving the brush across and off the other side. Then do the same back the other way — back and forth until all the brush strokes are lined up and the bubbles "The trick to reducing problems, such as bubbles, runs and sags, is to work in a reflected natural or artificial light." almost gone. The remaining bubbles should pop out on their own. Then apply the next 6" to 12" in the same manner, working the finish back into the last inch or so of the previous application. Continue until the surface is covered. The trick to reducing problems, such as bubbles, runs and sags, is to work in a reflected natural or artificial light. This is the critical instruction that is rarely given. If you move your head so you can see your work in a reflected light while you're brushing, any problem that occurs will become quickly apparent, and the solution will be obvious. In most cases, it is to brush back over the area and stretch the finish out thin. You should use as clean a brush as possible and work in as clean a room as you can, but there will still be dust nibs when the finish cures. Sand these out between each coat. When the finish looks good — after two or three (maybe four) coats — it's done. Leave the last coat unsanded. Applying Wiping Varnish You can apply wiping varnish exactly like polyurethane by brushing coat after coat onto the wood. Or you can wipe on, and then wipe off, most of the excess. The more excess you leave, the greater the build. This second method is the easy one, and the way wiping varnish is usually applied. It's an almost foolproof finish when applied in this manner. Again, the trick to achieving good results is to check the finish for flaws in a reflected light as you're applying it. pw Bob Flexner is a nationally known finishing expert in Norman, Oklahoma, and the author of "Understanding Wood Finishing." |
