In Finishing

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Years ago I remember teaching a class about finishing that included one student who said he had never used a stain or finish, and to make matters worse, he had never even painted anything. This was a two-day class in which I go through all the products and application methods. How was I going to address this student’s lack of any experience at all? Here’s an attempt, addressing you the reader, rather than him. The steps are sanding the wood, deciding on the color and maybe applying a stain, and deciding on a finish and applying it.

The first step is to sand the wood so flaws won’t be highlighted by a stain or finish. Flaws in the wood, like machine milling marks, scratches, gouges, etc., have to be sanded out or filled with wood putty before applying a stain or finish, or these flaws will be highlighted. Begin with a grit sandpaper coarse enough to remove the flaws efficiently, usually with 80 or 100 grit. Sand in the direction of the grain when possible and back the sandpaper with a flat block when sanding flat surfaces. Then remove the coarse-grit scratches with finer grits: 120, 150, and 180. You can usually skip a grit, but it depends on how long you sand with each.

Machine milling marks, also called “washboarding,” are caused by a jointer or planer, and sometimes a shaper or router, that isn’t tuned perfectly. The reason for the name washboarding is pretty obvious.

When sanding a flat surface like a tabletop or cabinet door, back the sandpaper with a flat block to keep from hollowing out softer spring-growth grain.

Unfortunately, knowing which grit sandpaper to begin with, when it’s time to move to the next finer-grit, and when the wood is ready to be stained or finished, can be learned only from experience. You can look at the wood in a low-angle, raking light, and even wet the wood with mineral spirits (paint thinner) as an aid to spotting remaining flaws. But even these tricks don’t always work.

You can see what the wood will look like with only a finish applied by wetting the wood with a liquid, such as paint thinner. If the wetted wood isn’t dark enough or the right color, you’ll have to use a stain. Oil stains are easier to use than water-based stains, which dry very fast.

No matter which stain you use, the method of application is the same. Using any application tool, apply a wet coat and wipe off the excess before it dries. Begin working on smaller surfaces such as legs and drawer fronts to get a feel for the drying time. If the stain dries too hard to wipe off, reliquify it by applying more stain right away, then remove the excess immediately.

The basic way to apply a stain is to wipe or brush it onto the surface and wipe off the excess stain before it dries. Try dividing large projects into smaller areas so there’s a better chance of avoiding drying.

Apply the stain and remove the excess from one or more complete surfaces at a time. Don’t overlap the stain onto a surface that has already dried or the double application may cause a difference in color.

A finish is necessary to protect the wood from water damage, dirt, stains, etc. You can apply a finish either directly to the wood or over a stain after it has dried. It’s always better—that is, more attractive and protective, to use a stain and finish packaged separately than a stain-and-finish combination.

In my opinion, the two best finish choices for a beginner are oil-based polyurethane in a satin sheen and wiping varnish. Wiping varnish is oil-based varnish or polyurethane thinned about half with paint thinner. You can make your own if you like. Common brands are Waterlox, Seal-a-Cell, Profin, Formby’s Tung Oil and Salad Bowl Finish.

Just like water-based paints, water-based finishes dry faster, are easier to clean up and have less odor, but they raise the grain and are more difficult in combination with stains.

Polyurethane is best for surfaces that get a lot of wear. Wiping varnish is best when you want a thinner, more flawless, finish.

Applying Polyurethane
Apply polyurethane using a bristle or inexpensive foam brush about two inches wide. 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 dried (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.

To brush vertical surfaces without runs and sags, arrange the lighting so you can see what’s happening in a reflected light. When you see the finish begin to run or sag, brush over the problem with the brush fairly dry from wiping it with a clean cloth to remove the excess.

On flat horizontal surfaces like 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 six-to-twelve inches of surface covered, line up the brush strokes. Do this by lightly bringing the brush down near one edge in an airplane-like-landing motion and moving the brush across and off the other side, back and forth until all the brush strokes are lined up and the bubbles gone.

Then brush the next six-to-twelve inches 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, usually to brush back over the finish and stretch it out thinner or remove it.

Always use as clean a brush as possible and work in as clean a room as possible, but there will still be some dust nibs when the finish dries. Sand these out between each coat. For the last coat you can rub lightly with a folded brown paper bag.

Applying Wiping Varnish
You can apply wiping varnish exactly like polyurethane by brushing, or you can wipe on, then wipe off, most of the excess. The more excess you leave, the greater the build.

To make your own wiping varnish, thin some varnish or polyurethane about half with mineral spirits (paint thinner). Do this in a separate container.

Wiping is easier and this is the way wiping varnish is usually applied. It’s an almost foolproof finish when applied in this manner. Work in a reflected light.

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