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The one aspect of woodworking that causes the most distress is finishing. It is saddening to see a finely constructed piece which appears to be of poorer quality only because of the finish. The finish is what most people see when they look at a piece, and it can make a poor piece look good if done right. This is how many furniture companies survive. They make a cheap piece and put a good finish on it and it sells well.
Finishing, like most aspects of woodworking, is an individual thing. Most woodworkers develop their own technique which works for them. In this article I will try and describe methods which work for me and will also work for novice workers as well. I do not intend to presume that my techniques are the best and certainly encourage anybody to develop their own. I primarily use three types of finish, penetrating oils, urethanes, and lacquer, and these are what I will discuss.
Planing - One of the greatest pleasures of woodworking is using a finely tuned hand plane. It imparts a sort of soothing meditative feeling. The songs each type of wood produces as the razor sharp blade slices it's way through each layer, is a joy to my ears. Watching the thin full shavings spew forth is exhilarating. The surface left behind is smooth and very slick. It would seem that this is the ideal method for smoothing a surface, that is until you run into a stubborn piece which leaves small chunks of wood missing here and there. This is called tearout and can instantly transform a beautiful experience into a nightmare. Many woods, especially tropicals, have interlocking grain (rowed) which is generally very troublesome. To imagine what it is like, interlock your fingers of both hands keeping them straight and that is exactly what the grain is like. Woods which are called ribbon grained are rowed. These can often be planed by taking diagonal cuts, but will need scraping or sanding to achieve a really smooth surface. The woods with crazy figures, wild grain, lots of knots etc. are the real plane breakers. But, at the same time they are some of the most strikingly beautiful woods. These woods yield best to other means of smoothing.
Scraping - Scrapers were the first tools used to smooth surfaces and still are necessary shop tools. Scrapers will tame almost any wood. It is possible to smooth an entire surface with a scraper alone. It is most used to remove plane marks and any small tearout produced by planing. Scrapers are generally a thin piece of semi- hard steel, and can either be of a square or curved shape. Also freshly cut glass, old plane blades, and saw blades can be used. They can be hand held or fitted to a holder with a sole called a scraper plane. For large surfaces the scraper plane is easier on the hands and the sole helps get a flat surface.
Sanding - Sanding is by far the most common method of preparing a surface for finishing. Sanding can be done by hand, machine, or a combination of both. IMO, if using a machine, the final sanding should be done by hand using a sanding block on flat surfaces. For odd shaped surfaces a folded piece of sandpaper or a piece wrapped around a piece of felt will suffice. There are some commercial devices called Tadpole sanders that come in various shapes which work very well for odd shaped pieces, especially moldings.
One of the reasons that sanding gets such a bad rap is that the monotony of the process often excuses a less than adequate job to be done. It is very important to remove all imperfections with the first grit used. The idea that the next grit will finish off is not correct and is the major reason for poor sanding jobs. The first grit removes all imperfections and subsequent grits only serve to remove the scratches from the previous grit. For penetrating finishes 180 grit is sufficient for surface prep, while for surface finishes 320 is fine enough. The finer grits are used for leveling and polishing the finish.
My method for using this finish starts with preparing the surface using one of the above methods. Next apply a liberal amount of the finish keeping the surface wet, allowing as much as possible to penetrate the wood. Keep this up for 20 minutes or so then leave it alone, don't wipe it off. The next day I usually find that all the finish has been absorbed. The next step is to steel wool the surface if it had been sanded previously or wet sand if not. I use either 320 wet and dry sand paper or 00 steel wool. With sandpaper I use it with the finish as a lubricant. The wet sandpaper will produce a slurry from the wood dust and finish, this can be used as a filler if desired. Sand with the grain as usual but do it lightly to just smooth the surface. If using the slurry as a filler let sit for a few minutes and rub against the grain with a piece of burlap cloth and then lightly with the grain using the same cloth which should be filled with slurry. This helps keep the cloth from removing the slurry from the filled grain. If not filling the grain, use a cotton cloth saturated with the finish and rub the piece well, removing as much residue as possible.
For steel wool, rub the wood vigorously with a dry pad of 00. The idea is to polish the finish filled wood. Steel wool is unique in that it both cuts and burnishes the wood. Some prefer to use abrasive pads but they will not burnish and consequently will not give the same polish. Rubbing hard will give a better polish as the wool quickly looses its edge and begins burnishing. You will find that every time you turn the pad it seems to cut better, this is because new edges have been exposed. Learning to use this knowledge is a good idea as you can control when it cuts and when it polishes. Next brush and vacuum the piece well then rub down with a cotton cloth, cheesecloth polishing cloths or old t-shirts work well. Then brush it again. For both techniques, apply the finish sparingly with a cotton cloth. Rub hard, heating and forcing as much finish into the wood as possible. Rest a few minutes and then rub it again with a dry cloth, removing all excess finish.
After the finish has dried - usually 24 hrs., but dependant on the finish and the environment, can be days - rub again with 000 steel wool this time. This applies to both previous methods. However, if the fill method was used a day or two longer will be required for the filler to be properly dried before rubbing. Apply finish as above. Repeat the steps over but using 0000 steel wool. Repeat his several times until the desired finish is achieved. The rubbing with a soft cotton cloth after steel wool will polish the surface even more, and when after doing this the surface looks like you want, you are there. This step is necessary as will be evident if you try this method.
Preparing the surface is the same as for oils except I usually sand to 320. I thin the first coat 60/40, varnish/mineral spirits or naphtha. Most varnishes use mineral spirits as a solvent but a few use VM&P naphtha. I feel that it is best to use the same solvent. Apply with a good quality bristle brush. China bristle is fine. It is good practice to dip the brush in the solvent first, this will make cleaning easier and seems to make the flow from the brush better. Shake out the excess thinner before dipping into the varnish. Don't brush back and forth any more than you have to. Long slow stroke will lay down a nice film and create less bubbles. The first coat will be mostly absorbed and will look pretty bad, but that's okay.
As each succeeding coat will not be absorbed by the previous one it is necessary to scuff the surface between coats. I rub the first coat down with 2/0 steel wool. When doing this you should be producing a fine white powder, if not and the steel wool is clogging, then the finish has not properly dried. It is important that the finish be dry between coats, but it is also important to not exceed the manufacturers recommended time between coats. The finish needs to be dry but not cured for proper adhesion of the next coat. It is imperative to remove all residue between coats using a brush, tack cloth and vacuum. Also the finishing environment should be as dust free as possible. Any residue or dust which is on the surface will be entombed in the next coat. The second coat requires a little more care in brushing as it will probably lay on the surface. Good strokes are important as is tipping off. Tipping off is holding the brush at 90° and very lightly brush long strokes. This will remove most bubbles and brush marks. The second coat and all others should be full strength unless the varnish you are using is very thick and does not flow out well. In this case you may need to thin a small amount, 5-10%. It is dependant on the varnish and should be thinned just enough to get good flow.
After the second coat is dry, sand with 320 or 400 wet and dry sand paper dipped in water for a lubricant. I usually splash a little water on the surface when possible. A sanding block should be used, as the purpose of this sanding is to level the finish and remove any contamination which may have fallen on the project. Wipe off occasionally and you will see small shiny spots which tell you where the low spots are. The pores of heavy pored woods will show up as shiny spots also but the next coat will fill most of these if you do a good job of sanding. The idea is to get a level playing field, so the low spots can catch up. Wipe the piece down well and wait a few minutes, then lightly dry sand in case you went through the finish and have raised some grain. Repeat this process again and this time the surface should be level. Often this coat is the last but on porous woods and if other problem arose you may need one more.
After the last coat you can either buff the piece with 4/0 steel wool, which will give a satin appearance, requiring only a buffing with a soft cloth to finish up. Or if you want a glossy appearance you can either rub with 4/0 steel wool or wet sand with 600 sandpaper. - The varnish finish itself will be very glossy and it is tempting to leave it at that, but this is what gives it it's bad name as a plastic looking finish. The rubbing process will transform it into a beautiful finish. Then you can either rub down with 4f pumice mixed with water for gloss or oil (paraffin) for semi-gloss. Or you can use auto rubbing compounds which come in varying grits. If you want a high gloss you can rub with rottenstone and water with a felt pad or use auto polishing compounds. You can use many different grits of micro paper but I find it to not work as well and uses a tremendous amount of expensive paper.
Solvent lacquers should be reduced about 50% with the recommended reducer for the product. There are reducers to compensate for heat and high humidity, low humidity, low temps etc. It is good to buy from a knowledgeable source and ask a lot of questions. Brushing lacquers do not require reducing and will not benefit from it.
Preparation is the same as for varnish other than the need for sealers. After sealing and sanding to the point you feel it is ready the finishing begins. For spraying - First spray a few mist coats to get a little build on the sealer, then a full wet coat being very careful not to create runs. Every gun and every brand finish is a little different so it is very wise to practice on a scrap piece first. Practice distance and speed and air mixture settings until you are comfortable. I like to get a couple of wet coats on before sanding. Sand lightly between every couple coats with 400 - 600 grit. It is not a good idea to use steel wool with lacquer as the wool may contain contaminates which will cause fish eyes. You can put on several coats in a short time but don't try to put on too many without allowing to cure. 3-4 in an hour is about right. Then after a couple hours do 3 or 4 more. Then let cure over night. It is hard to say how many coats to put on but for a fine finish it takes quite a few. Remember that the coats are thin and they melt into the previous one so it takes a lot to get a good build. Of course a few coats will give an adequate finish but not a fine finish with great depth.
Brushing - Brushing is a little more difficult but can give good results. One advantage is that each coat is much thicker and only a few coats are needed. Use a fine bristled brush dipped in lacquer thinner to prep the brush. The first coat will flow on easy but the next will be a little more difficult. Sanding between coats is recommended using 400 grit. After the first coats the brush will drag a little as the new finish melts the previous one. You will need to go fast but still take care. With brushing a thick coat is usually better but be careful not to make it too thick, you want it to level.
The last coat can be rubbed with pumice, rottenstone, rubbing compounds, but needs to be rubbed. To get the full effect of this beautiful finish it needs to be polished with polishing compounds to the finest grade. Polishing with the grain will give the appearance of no scratches. Rubbing and polishing is like sanding, first you scratch up the surface getting rid of imperfections and then you must get rid of all the scratches. If the finish is not thick enough it is fairly easy to rub through it. Fortunately you can re-coat as many times as you want at any time. Rubbing should not be done for a couple days to give the finish time to cure.
Silicone - This stuff is bad for all finishes, do not use anything which has it in it. It causes craters called fish-eyes which will cause great consternation. Fish-eye retarder is silicon in disguise, if you use it you will have to always use it as it will contaminate your spray equipment and brushes.
Lastly, invite over a few friends, break open a bottle of good wine and enjoy the fruits of your labor. Enjoy!
Gary Straub
gstraub@peoplepc.com Columbia, MO
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