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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 many Internet forum discussions, my experiences, and discussions in our woodworking club and in demos at the local Woodcraft store. And if you want to jump ahead, see my comments on why I switched to water base finish.
Everyone wants a finish that looks good, wears well, and protects the underlying material for a long time. 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:
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 described below.
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 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, 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.
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. 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. Don't assume that leftover house paint will be fine as a primer coat on your painted bookcases.
Many types of antique furniture used different types of wood for different parts - the curved back of a Windsor chair is usually a different wood than the deeply carved seat. 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 furniture. Think enamel instead, unless you are making reproductions.
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 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.
This historically traditional film finish is on the surface of the wood, so protects the wood and allows dirt and body oils to be cleaned off the surface. 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. As a solvent-based finish, the solvent in subsequent layers melt the new layer into the earlier layers, 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.
With shellac, varnish, lacquer, and 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 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, but dries 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 spray finish. It was once used for cars, and is still used in finger nail polish. It is a solvent finish, so it 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. 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... repeat for other materials).
Nitrocellulose lacquer, also called "traditional" lacquer, or solvent-based lacquer, stinks, literally, until it dries. The solvent is a flammable hydrocarbon (think gasoline). Californians call it illegal, chemists point out that after it evaporates from the finish, the solvent oxidizes, leaving byproducts that are similar to the fuel burned by our cars. It is not a flourocarbon like the air conditioning gasses that were destroying the atmosphere.
A couple points to scare you into being careful with Lacquer... but hopefully not to turn you away from this great finish. I know of a furniture repairman whose shop/barn (full of antiques being restored) burned to the ground after he sprayed some lacquer. I know a doctor who treated a woodworker with third degree burns (charred flesh) from a lacquer fire. I know of a furniture maker who sprayed in a well ventilated shop, finished, and closed up while he cleaned up. They found his body in the shop the next day.
So why would I consider something this dangerous? Great finish, fast, easy to spray. It is so fast drying that few people can effectively brush it on. But I live in Texas, so can spray outdoors most of the year. Lacquer drys so fast, that the overspray is dry before it hits the ground (you should even hold the spray gun closer to the work than you would with slower drying finishes). I often spray outdoors in the driveway, and stay at least 3-5 feet away from the cars - I have had no sign of overspray on either car. If you must spray indoors, beware of exhaust fans - motors cause sparks. Try blowing clean air into your spray area, and vent to the outside without blowers.
Traditional nitrocellulose lacquer is fairly thick as you buy it. A top-of-the-line spray rig may be able to "atomize" the lacquer with little or no thinning. But most people find that a mix with 30-50% thinner works pretty well. If you thin too much, the finish may drool, and you may need more coats (the thinner doesn't add to the finish you are trying to "build"). But if it is too thick, the tiny droplets created by the spray gun may not be very small, and they may not flow together to make a smooth finish (often called orange peel, because the texture is like the skin of an orange). There is no perfect answer to the amount of thinner - it depends on the operator, the gun, the air supply, the temperature, the air pressure and volume in the gun, the paint volume, and perhaps the phase of the moon. If you are just starting, try 1/3 thinner - if the finish doesn't "flow smooth" add more thinner. If it works good, try less (thinner doesn't add to the finish, just to the cost and number of coats required. You will quickly become an expert.
Regular lacquer can be sprayed over a very wide range of temperatures. I have heard of people spraying below freezing, although I haven't worked that cold. I have sprayed with the work piece well over 100 degrees in the mid-day sun. But regular lacquer hates high humidity. As the solvent evaporates, the finish cools; if the humidity is high, moisture condenses into the finish, and leaves the surface milky. (Apply another coat of thin lacquer, when the humidity is down, and the problem should disappear.) One rule of thumb is that if even part of the sky is blue, the humidity is probably low enough. When evening comes and it starts to get dark, you must quit. But one day I got up early when the sky was blue, and learned that the blue sky rule was just a guideline... don't start too early!
The BLO, Tung Oil, or Oil mixture is applied by brush or other technique. The key is that anything that doesn't soak into the wood in 5-10 minutes should be rubbed off before it dries. Many oils give off heat as they dry, so be sure that you don't leave oily rags in a pile where the heat can build up... it can start a fire.
Use a good brush and technique... don't expect a great finish by casually spreading the finish with a $1 disposable brush from WalMart. The material must dry slowly enough and be thin enough so that it can flow - level but not drool - to eliminate brush marks before it dries. It must be thick enough to build the finish.
You can buy a special wipe-on finish, or can thin most regular finishes (perhaps 50% paint thinner). The finish is wiped on with a rag or sponge brush. Each coat is so thin that there are no brush strokes. Each coat dries fairly quickly, but many coats are required to build the film thickness to protect the furniture.
This is a special technique that mixes multiple finishes to lubricate the pad that is used to wipe on the finish. Special pad (called a tampon), special technique, special mixture of finishes, time consuming to learn and do, but great results.
Once you learn to spray, you won't go back. But it does require skill. One instructor said, "If you have an air compressor, buy a "conversion" gun and a gallon of lacquer, some lacquer thinner, and for $150, you will learn to spray and have the equipment." It does require skill - I have had a spray outfit for over 40 years, and am still learning. It is definitely the way to go. Someday I will build a web page about spraying techniques, but this isn't it.
There are lots of names for the amount of light reflected from the surface, but the most common (unencumbered by marketing hype) seem to be
The final sheen is determined by how much the reflected light is diffused, achieved in either of two ways...
If I want a very smooth surface, whether satin or gloss, the grain must be filled.
If the wood is smooth to begin with, like cherry. the first coat of finish, or a coat of shellac, can be used as a sanding sealer. After the coat is applied, filling the pores, the bulk of the sealer is sanded off - even down to the surface of the wood, leaving a perfectly level surface. A specific sanding sealer product is a first coat that has extra chemicals (often stearates, nicknamed "soap"), to allow easy sanding without clogging the paper. As a softer material, sanding sealer should not normally be used to build the thickness of the finish.
If the wood has open grain, like oak, and I want a very smooth surface, like a desktop, I use a separate wood filler. They can be oil or water based; many use pummice or other fine-ground mineral as the actual filler, so a quart of filler may be much heavier than a quart of paint. My favorite is Behlens water base grain filler, in either natural (light) or dark tone. It is spread across the grain and rubbed in, dries quickly, and is easily sanded. It takes stain well, but as a mineral, does not color well with dyes.
If you are going to rub out the finish, you should use gloss material. Some people argue that all the build coats of finish should be gloss, even if you are going to use a satin or other sheen for the final finish, so the "grunge" doesn't obscure the grain (a very subtle point, if valid at all). In either case, the bulk of my finishing is done with gloss, which is nice since I have found gloss finish requires less stirring and filtering.
Super-fine sandpaper Most sandpaper for machine sanding goes as fine as 220 grit - occasionally 320 grit. I found a Festool 400 grit (ignoring the Titan2 that is sterated so cannot be used on wood or if any water base finishes are involved). Then I found Mirka Abranet. It is like a screen with abrasive surface, available up to 1000 grit. Individual sheets are expensive, but whole boxes make the cost reasonable. Be sure to get an interface "protector" pad to use between your sander and the Abranet - long hooks on some hook-and-loop pads hang through the screen and are sanded off (see my Festool experience). |
After the first coat or two of finish, which may raise the grain or show flaws in my preparation that need to be fixed, I machine sand at 400 grit (or less if I am fixing something that should have been taken care of earlier in the process). This gives a great surface to build the several coats of finish. If I have a drool or other flaw, I may machine sand again at 400 grit, or if I am trying to build a thick finish, I may sand after several coats (or just before the final coat), to keep the working surface absolutely smooth.
If the goal is a gloss finish, I may try a quick sanding with a 1200-2000 grit pad after the final coat. If that removes dust nibs or other imperfections, I am done. If I was having an off day, the the finish isn't good with the quick touch-up, I drop to 400-600 grit machine sanding (hand sanding edges and corners), and work may way back up.
If the goal is a satin finish, machine sanding to 600 grit works pretty well. Contrary to general directions, which suggest waiting until the finish has cured for a couple days, I do it after lacquer has dried for a few hours. After the machine sanding, rubbing with a towel smooths the sanding marks (the finish is a little soft) in addition to cleaning.
If the goal is a semi-gloss finish, machine sanding to 800 grit followed by a similar towel rub works well
I have not found inexpensive pads for machine sanding that are finer that 800-1000 grit (the quick sanding mentioned above is done with expensive sponge-back sanding pads cooled with a mist of water). Therefore I switch to rubbing compounds. I have not tried a lot of options, but had several recommendations for the Menzerna compounds, applied with Surbuf pads on my ROS. This works well for me.
For a larger project like an entertainment center or set of bookcases, a hand-rubbed finish doesn't add value for my customer. If I have an open grain like oak, a hand rubbed finish needs to be filled or the open grain will be shiny while the surface is satin. Therefore, there are times that I do actually spray a satin or semi-gloss finish. It is only used for the last coat or two, and I usually do the machine sanding before these final coats (since I learned not to try to rub out a finish with "grunge."
I plan to keep adding to this page... send me your suggestions! Don't forget to look at my page on water based finishes.
Good luck!
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