Popular Woodworking 2008-12 № 173, страница 61

• Flexner on Finishing •

BY BOB FLEXNER

Howto Brush a Finish

Putting some sense back into a simple task.

the boards (to be followed presumably by the next foot, which would leave a distinct overlap) instead of using long si rokes runn ing t he length of the top.

Though this method is counterintuitive, and most people will figure out very quickly that it produces unacceptable results, the authority presented by TV and a brand-name company can't help but lead some people astray. (For example, a senior salesman from a major paintbrush manufacturer came to my shop once and used this method while we were trying out different brushes.")

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I or most people, the first experience brush-ingcomes wit h oil or lalex paint, or wiih alkyd or poly urethane varnish. Each of these coatings is relatively easy to brush.

Paint is easy because it doesn't have to go on perfectly; brush marks and other minor flaw⁷s are expected and accepted. Varnishes are easy because they dry slowly, so there's plenty of time to spread them out evenly and get the brush strokes lined up with the grain.

Polyureihane varnish is the finish most widely brushed by amateur woodworkers, and ii is the finish that is almost always used in instructions on how to brush. (See "The 7 Myths of Polyureihane" in the finishing section at popularwoodworking.com.) There are countless articles, several videos and even segments of television ads that describe or demonstrate how to brush varnish.

For a reason I don't understand, almost all ofthese instructions suggest or show brushing slowly, several at the incredibly slow speed of eight seconds per foot. (Try it; I'll bet you can't brush this slow the first time).

There was even a recent TV ad from a major finish supplier that showed brushing the entire width of a tabletop only 1' in from the end of

Reflected light. When there's no light reflected in the surface 'left), you can't see problems as they develop. Move your head to pick up a reflection from some light source so you can see what's happening - for example, the runs and sags in this finish (right). Once you see a problem, it's usually easy to fix, most often by brushing back over the surface.

Brush differences. Brushes differ in their ability to keep their bristles from falling out, in the amount of finish they can carry and in their comfort. More expensive brushes, such as the oxhair brush 'top), don't reduce brush marks noticeably over the very cheap chip brush (middle), or the foam brush (bottom). The finishes themselves differ in how well they flatten out.

Though it's also somewhat counterintuitive, many instructions suggest brushing across the grain, or diagonal to it, before lining up ihe brush strokes with the grain. Other instructions caution against shaking the finish, or even stirring it, because this will introduce air bubbles.

Brushingisvery simple, actually intuitively simple. It shouldn't require a magazine article like this one to put common sense back into the process.

The Basic Rule

The most critical rule for achieving good results, and the rule you almost never see, is to waich what you're doing in a reflected light. This rule holds for spraying just as it does for brushing.

You can see what's happening in a reflection, and you can't see i f t here isn't one. As long as you see a problem as it occurs (usually a run, sag, drip or bubbles), it is usually easy to fix simply by brushing back over the surface.

Bristles or other trash that may have fallen into the finish are also easy to spot in a reflected light, and they're easy to remove with the tip of the brush or a small toot such as a toothpick.

82 ■ Popular Woodworking December 2008

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