Twenty Questions on Finishing

Fading finish. Notice the fading and finish deterioration in the top two-thirds of this cabinet, which backed up against a west-facing window for many years.

Did I mention there would be a quiz?

Here are 20 questions, together with the answers, based on my articles from Popular Woodworking. If you have been reading regularly, you should do well.

For more in-depth explanations, go to the finishing section of the site, where you’ll find many of the articles, and you can find explanations in my book, “Understanding Wood Finishing.”

True or False?

1  ■  The crucial element causing finish deterioration and color fading is light.

True. Especially UV light from direct sunlight and fluorescent light.

2  ■  The purpose of a sealer is just as the name implies – to seal the wood.

False. The first coat of any finish seals the wood. A “sealer” solves a problem. Sanding sealer makes sanding easier. Shellac blocks silicone oil, pine resin and bad odors.

3  ■  Washcoating refers to the procedure of washing the wood with a solvent to clean the wood before applying a finish.

False. Washcoating refers to partially sealing the wood with a thinned finish before applying a stain to reduce blotching.

4  ■  Many products labeled “tung oil” are not tung oil at all.

True. Most are varnish thinned about half with mineral spirits. They have nothing to do with tung oil.

Glazing and toning. Both of these processes are a way to add color over sealed wood. Glazing (above) involves applying and manipulating a thick-pigmented stain; toning (below) is a thinned and lightly colored (pigment or dye) sprayed finish.

5  ■  Glazing and toning are two ways of adding color over sealed wood. Which of the pictures above shows glazing and which shows toning?

The cabinet door on the top was glazed. That is, a thick-pigmented stain was applied and selectively removed and brushed out to create the darker coloring in the recesses and on the edges. The cabinet door on the right was toned. A colored finish was sprayed into recesses and on the edges and left. It wasn’t touched.

6  ■  The only way to get a perfect finish, despite many claims to the contrary, is to sand the finish level and rub it to the sheen you want using various grades of abrasives.

True. Unfortunately. The phrase “perfect finish” is way overused.

Orange peel. The finish on the left side of this photo was sprayed too thick with too little air pressure. The orange peel was avoided on the right side by thinning the finish.

7  ■  The way to avoid orange peel (seen in the photo at immediate left) is to increase air pressure, thin the finish or both.

Both. These are the remedies because the primary cause of orange peel is spraying too thick a liquid with too little air pressure.

8  ■  The basic instruction for applying a stain is to apply a wet coat and wipe off the excess before it dries.

True. It’s critical that the wood first be wet with stain to get an even coloring.

9  ■  Always apply compatible oil or varnish (polyurethane) finish on oily woods such as teak, wenge and cocobolo.

False. The oily resin in these woods hinders the drying of oils and varnishes but not other finishes. To get oils and varnishes to dry normally, clean the oily surface of the wood by wiping with naphtha just before applying the finish or apply a coat of shellac to block the oily resin.

10  ■  Always brush stains and finishes across the grain first to work them into the grain.

False. Stains and finishes soak into the grain of wood by capillary action no matter in which direction they are brushed.

11  ■  Finishing undersides and insides of a project prevents warping.

False. Finish only slows moisture penetration; it doesn’t stop it. If the wood isn’t dried properly for the climate, it will still warp.

12  ■  Other than spraying, the most efficient way to apply a stain is to brush it.

False. It’s much quicker to wipe on a stain using a cloth or sponge. Then wipe off the excess.

13  ■  Always begin sanding wood with #80-grit sandpaper to remove flaws.

False. The grit sandpaper to begin with varies depending on the situation. Always begin with a grit that removes flaws, such as washboarding, snipes or gouges, efficiently without creating deeper-than-necessary scratches that then have to be sanded out.

14  ■  Judging by the amount of color the finish adds to the wood, which cherry panel of the two pictured below is finished with water-based polyurethane and which with oil-based polyurethane?

The colorless left panel is finished with water-based polyurethane. The richer right panel is finished with oil-based polyurethane.

Oil vs. water. Oil- and water-based polyurethane look very different on wood. Water-based polyurethane (above panel) adds no color to the cherry. Oil-based polyurethane (below panel) adds a warmer yellow/orange coloring.

15  ■  Judging by the amount of color added to the wood in the left photo below, which side (left or right) would you think was stained with a common oil/wiping stain and which with a water-soluble dye stain?

The left side was stained with a common oil/wiping stain, the right with dye.

Oil stain vs. dye. Oil stain (left) doesn’t color the dense parts of oak as well as dye stain (right).

16  ■  The most important instruction to follow when brushing or spraying a finish is to watch what’s happening in a reflected light.

True. In a reflection you can see problems as they occur and fix them (see photo at upper right). Without a reflection, you’re blind.

Reflected light. Always check for developing problems in a reflected light.

17  ■  “HVLP” refers only to spray guns with air provided by a turbine rather than a compressor.

False. “HVLP” refers to a soft spray created by high air volume rather than high air pressure. Both air sources can produce this soft spray if the gun is made to do this.

18  ■  Blotching can be avoided in cherry by applying a wood conditioner before applying a stain.

False. The wood conditioner itself will cause blotching. Most cherry boards blotch no matter what you do. The only way to totally avoid this blotching is to cover and hide it with glaze, which obscures the wood, of course.

19  ■  The most widely used finish among amateur woodworkers, and the finish I’ve suggested produces the best results with the least experience, is wiping varnish.

True. Wipe-on Poly, Waterlox, Seal-a-Cell, Arm-R-Cell, Pro Fin, and many brands labeled “tung oil” are all wiping varnish – that is, varnish thinned about half with mineral spirits. You can make your own.

20  ■  Thinning the first coat of finish half with thinner creates a better bond to the wood.

False. Thinning the first coat makes it easier to sand, which should be done to create a smooth surface for subsequent coats. Thinning doesn’t improve the bond to the wood.