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I am not a finishing expert... Not a Jeff Jewitt, expert on applying finishes, nor an expert on finish chemistry like Chris Minick or Jeff Weiss. But I build custom furniture, primarily indoor furniture. And I have developed some feelings on finishes - strong feelings. These notes are based on my experiences, many Internet forum discussions, discussions in our woodworking club, and in demos at the local Woodcraft store. And these finishing techniques have changed, since I started woodworking full time, and the finishes themselves have changed. I also don't have a clean shop where a piece can dry for a week.
In addition to this overview, you can jump ahead to sheen and rubbing out the finish, lots more on lacquer, and spraying techniques.
Everyone wants a finish that looks good, wears well, and protects the underlying material for many years. Sorry. No miracles. Or if you have a miracle, let me know. The finest marine varnishes have to be renewed once or twice a year. The most permanent deck paint or stain only lasts a few years. So I am down to two suggestions for clear outdoor furniture finishes:
This finish is wonderful... Sand to 400 grit or finer, apply a few coats of Boiled Linseed Oil (BLO), Tung Oil, or other oil, wipe each coat "dry" then let it cure for days. Use steel wool, if necessary, to be sure everything is perfect between coats. After a few coats (and many days of drying), wax with paste wax furniture polish. It brings out the best in the wood, and feels absolutely wonderful.
Of course, the oil has soaked into the wood, and the wax provides little protection, so dirt and body oils accumulate in the finish. One fine furniture store explained that, after a few years, you should remove the wax, dirt, and any oil on the surface with steel wool, apply new oil, and wax. Sure, refinish your furniture every five or ten years. Not me.
A film finish such as shellac, varnish, or lacquer, stays on the surface of the wood, so protects the wood, and allows dirt and body oils to be cleaned off the surface. With basically all film finishes, the film will fill and hide the fine scratches in the wood left by sanding, so you only need to sand to 150 or 220 grit; not to 320, 400, or finer, as you would with an oil finish.
This is a historically traditional film finish. It comes from the Lac bug, and is dissolved in alcohol. It dries by the evaporation of the solvent (alcohol), without a chemical reaction to form the film, which means that the alcohol can re-dissolve the finish. As a solvent-based finish, the solvent in subsequent layers melt the new layer into the earlier layers (called burn in), creating a single layer finish, a tremendous advantage when applying or repairing the finish. But shellac is arguably soft, and definitely subject to water and alcohol damage (the white glass rings are often in shellac).
Shellac is a great finishing tool. It sticks to practically anything. It brings out the color and grain when applied directly to wood. And practically any finish sticks to it. As a tool - a primer or intermediate layer in finishing, I love it, but not as a final finish.
This is a traditional high quality film finish, readily applied by brush. It is a reactive finish, so "drying" is a chemical reaction that creates the film, rather than simply the evaporation of the solvent. The layers are hard and durable, but each layer remains separate (a challenge if you "rub out" the finish). With a slow drying time (as needed for most brush-on finishes), it is subject to contamination for longer than I can keep my shop clean. Varnish really needs a clean room, a high quality brush, and a skilled operator to apply well. I haven't got the clean room, time, or skill.
"Poly" is chemically different than varnish, but has many of the same characteristics. It is easily brushed on, dries faster than varnish, but still slowly enough to attract every dust particle within miles. If subsequent coats are applied within hours of the previous coat, the layers bond together; if the previous coat is totally cured, the surface must be sanded (scratched) so the subsequent coats will adhere properly.
Poly is very hard - so hard that it is very difficult to scratch. Therefore I love to use use poly on floors. But years ago I put poly on our "kitchen" table. Hard is also brittle. I don't know how they did it, but my son and his friends, as they were growing up, managed to chip the finish on the table. In my personal opinion, polyurethane is too brittle for furniture.
This is a traditional fast drying spray finish. It was once used for cars, and is still used in finger nail polish. It is a solvent finish that can be applied in multiple layers, that will "burn in" and become a single durable layer. If you need to repair or "rub out" the finish, there is no worry about rubbing through a layer and leaving a "witness line" where you transition from one layer to another. It dries fast enough that there is little or no problem with dust, and several coats can be applied in a single day.
Lacquer wears well on indoor furniture, and has passed my tests (spill wine on it, then set the wine glass in the spill for a few days, so it doesn't evaporate, and check for damage... repeat for other materials). Catalyzed lacquer includes extra chemicals that make the lacquer even more durable - less susceptible to chemicals. Acrylic lacquers are a high tech finish that are still more durable. Lacquer is the finish that I normally use for indoor furniture.
I strongly prefer showing the beauty of the wood without artificial color. But there are times when it is appropriate, normally applied under the final finish.
Dye changes the color of the wood fibers, rather than applying a color to the surface. The character of the wood is now different - the grain may be emphasized or masked, but it is not covered by the finish. Dyes may be water based or solvent based - there are arguments for both - but they are always covered with a film finish that makes them permanent. Bleach is often used to remove a dye.
Stain is a transparent paint that is applied to the surface of the wood. Sanding scratches and rough surface cause more of the color to "stick" in an area; fine sanding of the underlying wood reduces the amount of stain that "sticks." End grain (or areas of uneven grain in the wood) become darker, so extra fine sanding of the end grain can reduce the darkening. If I expect wood to become "blotchy" one solution is to sand to a very fine grit (400 or finer), and then lightly and evenly "scratch" the surface with a coarser sandpaper (such as 220 grit) before applying the stain.
Many commercial "stains," like the popular MinWax from Sherwin Williams, often sold at discount stores, are actually a mixture of stain and dye. The final character of the stain depends as much on the wood and wood preparation, and the application techniques, as the stain itself - matching another piece is a special art. Paint remover is often used to remove stain.
The clear "final" coats of finish can be tinted, making it a toner, to add shading or color tone. Note the color is in the finish rather than in or on the wood). This is different than a glaze, which is color applied under the finish coat, often to bring out the shadows or to "age" the wood. Some of the traditional finishes such as shellac and varnish were amber/yellow, so the newer "clear white" finishes can be tinted, like a toner, to have the more traditional "hint of yellow" color.
Paint is intended to cover and hide the wood. This allows use of materials that aren't naturally attractive - for example, MDF makes an excellent floating panel in a painted door. Paint is far higher tech than many realize. The beautiful black grand piano is not ebony but is typically maple wood coated with black paint under clear finish coats. Ceiling paint has better hiding power and reflection than wall paint, but little or no resistance to abrasion (wear). Wall paint is designed to withstand wear (touching and cleaning). Floor paint (ok, deck paint) is very hard - scratch resistant. House paint is very flexible, so it can expand and contract with the weather, thus is soft and less abrasion resistant. Don't assume that leftover house paint will be fine as a primer coat on your painted bookcases - it is far too soft.
Many types of antique furniture used different types of wood for different parts - the curved back of a Windsor chair is usually steam bent oak, the deep seat profile is carved from pine, and the turned spindles maple to show the sharp detail. Paint, such as "milk paint" was used to hide the differences in the wood. "Milk paint" is nasty stuff, but is still available if you are making antique reproductions. I have recently met several people who believed that milk paint was the preferred paint for all furniture. Think enamel for modern furniture, and leave the milk paint for antiques and reproductions.
Jump ahead to the page on lacquer, the page on rubbing out the finish and achieving the desired sheen, or to the page on spraying, or jump back to the index of woodworking tips.
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