By Dwight Klaus
Last update 5/18/03
If someone told me a year ago that I would be using water-based polyurethane for finishing all of my woodturnings, I would have called them crazy. Until then, I had been using oil based stains and varnishes exclusively. How could a water based product ever compete with the depth and beauty of a hand rubbed tung oil finish, or several layers of a premium quality varnish, or the depth and luster of eight sprayed-on coats of shellac?
Well, believe it because it’s true. And not only is the resulting finish as attractive and durable as the hydrocarbon based products, its MUCH easier to work with. I can apply many more coats of the water based finishes in the same amount of time as a single coat of the petroleum based finishes. Good quality polyurethane will dry as hard as varnish – which is critical to enable the film to be polished to a high gloss.
Be forewarned - in order to get glass flat results, this technique requires patience. It may not be for every person or every piece. I was taught that in order to do justice to your work, finishing should take about the same amount of time as constructing the piece – anything less and you are probably rushing the process. The largest component of time is consumed in filling the grain. A piece constructed with closed grain woods will finish much faster than one with deep pores. There may be other ways to fill the grain faster than with this finish, and get a similar quality of result – this is an area I am still exploring. The following sections explain the complete process I am following at this time. In my opinion, the beauty of the resulting finish is well worth the investment in time.
1. (+) No noxious or explosive fumes
2. (+) Environmentally friendly
3. (-) Water-based finishes raise the grain - first coat only.
4. (+) Easy cleanup. Hands and brushes wash clean with soap and water.
5. (+) Extremely clear finish – does not artificially accentuate or hide the natural beauty of the wood. UV blockers will resist fading.
6. (+) Dries quickly, and builds rapidly
7. (-) Must wait several hours before ready to sand
8. (+) Very hard and durable after fully dry
9. (+) Can be applied over most other finishes once they are thoroughly dry.
10. (-) Cost of finish is higher than other similar products.
1. General Finishes (800-783-6050) High Performance Polyurethane (Gloss) - $25/quart, $50/gal at Woodcraft
2. Windsor & Newton Series 240 no. 3 brushes - $15 at Michaels
3. Low RPM lathe (not a requirement, but will make this technique much more enjoyable)
4. Sandpaper – 120,220,320
5. Synthetic sanding pads – maroon, green, grey
6. Steel wool - #0000
7. Hair dryer – any inexpensive unit
8. Hand drill for sanding and buffing
9. Tripoli and White Diamond buffing compound and buffing wheel with arbor for drill
10. Renaissance wax - $19 from Woodcraft and many others
11. Muslin buffing wheel
12. Tooth picks for fixing minor voids and blemishes
13. Cotton rags
My bowls are turned on a face plate, with the open end facing the tail stock. I use a deep fluted bowl gouge to expose the exterior form, and then hollow it with a variety of tools until the wall is 1/8 to ¼ inch thick.
1. Fill any large voids using your favorite filling technique – I prefer CA glue w/ wood dust.
2. Sand to 320 grit or finer. I like to final sand in both directions of rotation, in order to lift any wood fibers that may be bent over. Lightly wetting the surface before the final sanding will reduce the amount that the grain will be raised by the first coat of finish. (Allow the surface to fully dry before final sanding.)
3. Remove dust from immediate area using compressed air and/or vacuum. Do not use a tack cloth – it will contaminate the surface. Allow time for any dust suspended in the air to settle. It is not essential that the finishing room be dust free, since the amount of time that the finish is wet is short. Just be sure that you can keep the area around your lathe free of airborne particles for the few minutes that they can stick to the piece.
4. Good lighting is critical. If you can’t see dust and defects, then you can’t fix them. I use two 100 watt lamps over my lathe – they provide bright focused light, and also help accelerate the drying process.
5. Ideally, according to the manufacturer, the temperature should be above 65 degrees. Lower temperatures will effect how the finish will level, causing fish eye or orange peel. Temperatures above 85 degrees and low humidity will accelerate drying and reduce the leveling time. General Finishes makes a retarder to extend the open time of this product, but I have never tried it. This being said, I have used this technique effectively from 50 degress to 110 degrees with no alteration, and very little noticeable difference in results.
6. Cover lathe bed under piece with drop cloth to collect any drips. The finish is going to occasionally drip off your brush while you apply it. Since it dries quickly, you don’t have a lot of time to clean up drips, and it will distract your attention from finishing the turning.
7. A typical bowl requires 1 pint of polyurethane – more or less depending on size of piece and openness of grain. If necessary, filter finish through cheese cloth to remove any lumps or impurities. I like to use small wide-mouth mason jars to hold a convenient amount of finish. Note that the finish will thicken as you reach the bottom of the jar – I usually add a small amount of distilled water on occasion to maintain its viscosity.
8. Plug in hair dryer, and blow out any dust before you begin. Check that the cord length allows you to comfortably apply warm air to the turning from a distance of approximately two feet.
9. Flick the brush against your hand to remove any loose bristles, so they don’t come off and stick to your turning.
1. Adjust lathe speed to approximately 60 RPM, then turn off. Speed must be slow enough to prevent centrifugal force from spinning the finish off, or causing the finish to concentrate at the widest circumference of the piece, under the lip, or the interior belly. Speed must be fast enough that you can level the entire surface before it dries. If your lathe cannot turn at slow RPM, then you can rotate the piece by hand. I used this approach while learning, and take it from me – your arm will get tired quickly! A better alternative is to hook up a pully to an auxiliary DC motor that can be adjusted for low RPM. Or, just buy a new lathe…
2. Mop on finish quickly to cover entire surface. Do not attempt to finish too large an area – finish must remain wet until leveling is complete. I finish the outside surface of larger pieces, then repeat the process on the inside surface. Smaller pieces can be finished in one pass. Be conservative with the amount of finish applied to the interior of enclosed forms, so the finish does not pool under the lip or in the belly.
3. Turn on lathe. Hold the brush steady against the piece moving it from the narrowest to the widest portion, spreading the finish evenly as the form rotates. Move quickly to completely cover the surface before the finish begins to set. Don’t apply any additional finish. If dry spots are discovered, leave them for the next coat.
4. “Tip off” the finish to remove brush marks and any remaining irregularities. The brush should now be damp but not dripping with finish. Hold the brush vertically and allow just the tips of the bristles to lightly drag along the surface as the piece rotates. Once again, cover the entire surface. Any irregular concentrations of finish will have a milky appearance – this commonly occurs at the rim. Lightly use the brush tip to level these areas, and it will pick up any excess finish.
5. With the lathe continuing to rotate, put the brush aside, and cover the finish jar. Hold the blow dryer 18 to 36 inches away from the piece and turn it on high heat. Gently move it back and forth as the form rotates, to accelerate the evaporation of water and cause the finish to set. I typically blow dry for two minutes – the finish will change from milky to clear as it sets. Once the finish has set, stop the lathe and inspect the surface. Don’t pick at any blemishes – they can be removed much more easily after the finish has completely hardened.
6. Clean the brush under warm running water. Hold brush upright and allow the water to flush all the finish out of the ferrule. Then spin the brush between your hands to remove excess water. Shape the bristles and stand upright to dry.
The initial coat of water based finishes will raise the grain - this can be reduced by lightly wetting the wood surface with a rag dampened with distilled water, then allowing the wood to dry before final sanding. I have not found this step necessary, since the raised grain can be easily sanded down after the first coat of finish.
Dip 1/3 of the bristles in the finish. Apply the first coat liberally, quickly covering the entire surface, using the brush as a mop. Don’t worry about bubbles – they will disappear when the finish is leveled. Rotate the piece by hand to make sure the entire surface has been covered.
Turn on the lathe at approximately 60 RPM. Starting from the narrowest part of the bowl and holding the brush steady, lightly drag the tip of the brush over the piece to level the finish – commonly referred to as “tipping off”. Allow the piece to rotate once or twice with the brush in the same location before slowly moving it towards the widest part. Centrifugal force will tend to pull the finish to the largest dimension of the bowl. If you find that the finish is collecting there, the lathe is spinning too fast.
For the initial coat, the wood will tend to absorb most of the finish. This is normal, since the finish is being used as a wood sealer. If you find that there is too much finish collecting at a specific section, lightly drag the tips of the brush across this area as the bowl rotates to spread it. If the brush is nearly dry, it will pick up the excess finish.
Allow the piece to continue to rotate, and set the brush and finish aside. Turn on the blow dryer and holding it several feet away from the bowl, gently allow it evaporate the finish. As the finish sets, it will turn from a milky color to clear, which I find takes about two minutes in the low humidity of the desert Southwest – this may take longer in other climates. Turn off the lathe after the finish has set, since it is no longer likely to sag. The finish is now dry to the touch, but still soft, so don’t touch the surface. Airborne dust will no longer adhere to the bowl.
It takes a few hours for the initial coat to fully cure – more or less depending on temperature and humidity. This can be accelerated with good ventilation, or by placing the piece in a warm or sunny location. I like to apply a coat in the evening before I go to bed, and then sand and re-coat the next morning.
Once the finish has cured, the surface will be slightly rough due the raised grain. I typically begin sanding with 220 grit aluminum oxide paper at 500 RPM, and lightly go over the entire piece. If the wood is particularly open grained, you can even start with 120 grit, but be careful not to sand through the finish. Don’t sand at high RPM, since this will generate heat that will melt the finish and cause it to become sticky or pitted. If the finish is properly cured, sanding will create a white powder and the surface will quickly return to being smooth. Courser grits will level the high spots, but leave the valleys glossy. The sandpaper tends to clog, so you must clear it with compressed air or by occasionally slapping it on the lathe bed. If that doesn’t work, switch to a fresh section of the paper. After the entire surface has a consistent scratch pattern, wipe the bowl with a clean cotton rag with the lathe running to clear away any sanding particles left by the paper.
Next, switch to sanding with a maroon synthetic pad. Repeat the procedures above until the sanding marks from the 220 grit paper have been removed. The synthetic pads do not clog as fast as aluminum oxide paper, but they still must be cleaned occasionally as white residue collects on them. I can typically sand several bowls with the same synthetic pad, as long as I clean it often and do not allow finish to cake up in the fibers. The sanding pads will conform to the surface and scuff the high and low spots to the same consistent scratch pattern. Again, wipe the surface clean of any sanding grit with a cotton cloth.
Finally, sand with a green synthetic pad in a similar manner. The surface should now have a matte finish with no sanding marks. If marks are still visible, it is necessary to return to a courser grit and repeat the process. I have noticed that some sanding marks will be covered by successive coats of the finish, but others will not, so I always make sure the surface is free of sanding marks before continuing to the next coat.
The same procedure described above is used to fill the grain and build a clear and smooth final finish. I typically apply three coats of finish between sanding to insure the film is thick enough that I don’t sand through to bare wood. On open grained woods, most of the finish is removed during sanding as the surface is leveled. More or less coats of finish can be applied between sanding, as long as the surface remains reasonably flat. If any ridges develop, the surface should be sanded flat before applying more finish. Don’t be overly aggressive with sanding – if bare wood is exposed, the grain will raise with the next coat of finish.
If one section of a turning uses an open grained wood, but other sections use a wood with smaller pores, you can selectively apply finish to the open grained sections. This will save on the amount of finish that you consume. Use the same technique as before, and taper the finish off between the open and closed grain sections, so no dramatic edge develops between sections with a different quantity of coats.
It takes me about ½ hour to sand the surface flat and apply three coats of finish. Then the bowl must dry thoroughly before repeating the process. I like to finish a piece twice per day, once in the morning and again in the evening. Using this approach, I can typically complete this phase in 2-3 days (12-18 coats of finish).
Drip a small amount of finish with a toothpick into any surface defects after each application sequence. Blow dry the region to set the drip so it doesn’t run. You can use the airstream produced by the blow dryer to encourage the finish to move into the defect area. After the finish hardens, sand these regions by hand with a fine grit sand paper to level them before continuing to sand the entire surface with the lathe running. This will gradually fill the defects until they completely disappear.
Inspect the turning carefully under bright light after each application sequence and sanding. After the grain is completely filled and the bowl has a perfectly flat surface, continue to the final coat.
The final coat of finish is applied using the same application technique. Only one coat of finish is required, since it will be lightly sanded and very little material will be removed. Mop on the finish, turn the lathe on and tip it off, then blow dry to set it and prevent sagging or runs.
After the finish has completely hardened, start sanding at 500 RPM with a green abrasive pad. Since the starting surface was flat, and only one coat of finish was applied, there should be very little surface irregularities to be removed. Sand until the surface has a consistent scratch pattern, then wipe clean with a cotton rag.
Now switch to a gray abrasive pad and sand again until any marks from the green pad have been removed, and the surface has a even matte finish.
Note: the white abrasive pads are too soft and do not remove any material, or noticeably improve the finish.
Finally, sand with #0000 steel wool. The piece should have a low gloss now, and be very smooth. Some pieces look best if you stop at this point, leaving a finish that is clear and smooth, yet has a slight whisper when touched.
I perform the entire process described above on each bowl before parting it off the face plate. The inside and outside is completely finished down to the base.
Next, the bowl is parted off and reverse mounted on either a jam chuck, or a vacuum chuck. I prefer the latter, since it is less likely to damage all the finishing work just completed. Use a closed cell foam or rubber gasket between the bowl and the vacuum chuck to cushion the bowl and help form a vacuum seal. I also bring the tail stock up to the base to help stabilize the piece as it is turning.
Turn the base to match the exterior profile of the bowl, and add a small concave depression at the center to form a rim so the bowl will sit flat. Sand the base with the same abrasive sequence that was used on the upper section. This will reduce any noticeable line where the top meets the base.
I repeat the entire grain filling, leveling and finishing process on the bottom, overlapping the region where the previously finished top section begins by an inch or more to allow the two regions to blend.
After a few coats have been applied to the base, I sign my pieces with India ink and a calligraphy pen (on light colored wood) or metallic gold ink (on dark woods), and then allow it to dry overnight. The next day, I apply a light coat of polyurethane over the writing – one quick stroke of the brush only! The water in the finish will dissolve the ink if you touch it more than once. If the signature does smear, you can wipe it (and the finish) off, and try again. Don’t worry if the finish is not evenly applied – you can sand it level after it dries. Apply a few more coats over the signature, blow drying each until the finish sets. Then sand the bottom with 220 or 320 sand paper to remove major defects, then green and gray abrasive pads to blend it into the sides.
The #0000 steel wool will still leave fine visible scratch lines in the final finish coat. These can be removed by buffing with finer abrasives.
Buffing can be accomplished using several methods. If the turning is still attached to a chuck, you can mount the buffing wheel on an arbor and attach it to a hand drill, then buff with the lathe turning one direction, and the buffing wheel spinning in the opposite direction. The Artisan Polishing System, available from Craft Supply (www.woodturnerscatalog.com) has all the components necessary to use this method.
If the turning has already been parted off, then you can mount the buffing wheel on an arbor with the appropriate Morse taper, insert it in the headstock, and use the lathe as a buffer. The Artisan system can also be configured for using this method. One warning on using this method: get a firm grip on your bowl with both hands as you buff – I’ve broken several pieces when they were ripped from my grip by the buffing wheel.
For those who are doing production quantities of finishing, a dedicated dual-arbor buffer is the most efficient way to go. These floor-standing units are the size of a grinder, and can accommodate two separate buffing wheels. I have seen a ¾ HP Baldor buffer go for under $300 from Enco (www.use-enco.com). Harbor Freight sells a heavy steel grinder pedestal for $20 which would be an ideal way to mount this buffer at a convenient working height.
You will need three separate buffing wheels – one for Tripoli compound, another for White Diamond compound, and a third for buffing after the application of wax. Do not try to use the same wheel for all three steps – you must not allow the grits to mix, as this will destroy your ability to produce a consistent surface. Also, I keep my buffing wheels in a Zip-Lock bag between uses, to keep them clean, and to prevent them from becoming contaminated with the other finishing compounds.
There are other methods of buffing the interior of a hollow vessel. I use Beall goblet buffs mounted on a tapered mandrel and attached to my hand drill to reach inside and buff the inside surfaces. The buffs use the same process and buffing compounds as the buffing wheels.
The first step is buffing with Tripoli. Load a buffing wheel with a small amount of Tripoli compound – just enough to color the wheel red. If too much Tripoli is clogging the buffing wheel, you can remove the excess by holding it against a piece of course grit sand paper until the excess compound has been removed. Evenly buff the entire exterior of the bowl. Repeat for the interior surface using a goblet buff. Wipe off any excess Tripoli with a clean cotton rag, and inspect the finish. The surface should achieve a consistent high gloss, and all remaining scratches should be gone.
Next, switch to the White Diamond buffing wheel, and repeat the process just described. Again – only a small amount of compound is required for buffing. The White Diamond compound is finer than Tripoli, and will continue to polish the surface. Switch to a goblet buff, and repeat for the interior. Wipe off any remaining compound with a clean cotton rag.
Finally, apply a wax coating to the surface to protect it from atmospheric contaminants and handling. I am currently using Renaissance paste wax, since it is compatible with polyurethane. Don’t use petroleum-based paste waxes – they don’t buff out well, and may damage the finish. With the lathe stationary, apply a small amount of wax to the surface using a clean cotton rag. Wait a few minutes to allow the wax to dry, then buff with a clean flannel buffing wheel.
Cracks and voids – drip a small amount of finish into the defect using a toothpick and blow dry until it sets. After it completely hardens, sand the area by hand with the lathe stopped until the surface is flat. Then sand the piece in the normal fashion described above to even out the scratch pattern.
Gummed up ridge – Occasionally, the finish may gum up in a ridge of hardened material during sanding. This is most likely due to excessively aggressive sanding and the accompanying heat. Hand sand the extra finish away with the lathe stopped, using 220 grit abrasive. When a smooth surface has been restored, turn on the lathe and even out the scratch pattern with the usual sanding technique.
Resurfacing – if the finish doesn’t come out right, you can always sand back down to bare wood and start again.
Recoating after waxing - wipe down with mineral spirits to remove the wax or other surface contaminants, then reapply.
Many folks will conclude that this is too complicated a process, and will return to other conventional finishing techniques. I like this process because I can get consistent high quality results, and this is critical to me after investing countless hours constructing a complex segmented vessel. I don’t mind the time investment because I know the finish will enhance the final product.
Some may choose to reduce the number of steps in order to limit the time investment, and this may be perfectly reasonable. For example, you can easily produce a very beautiful matte finish by eliminating the buffing steps, and substituting a final rub out with an auto body rubbing compound. I only use the gloss polyurethane rather than matte, since it is easy to reduce the shine to any appropriate level.
In any event, the important point from my perspective is that your work is the highest quality that you can make it. I haven’t found another finishing process that I like nearly as much as this one, and until I do, this will be used on the bulk of my work. I’m sure that with time, refinements and improvements in these techniques will continue to enhance the finishing results that I can achieve.
1. Application of water based finishes over oil based grain colorants.
2. Use of grain fillers to accelerate the leveling process.
3. Wet sanding while grain leveling to reduce sand paper waste due to clogging.
4. Using the same process with other polyurethane products, in order to reduce material costs.
Many thanks go to Dave Ramsey who opened my eyes to water based finishes when he showed me this finishing technique. The depth of his experience has saved me countless hours of trial and error.
My appreciation to the members of the Arizona Woodturners Association, who have provided plenty of encouragement and constructive criticism – two necessary ingredients for any developing artist.
By Dave Ramsey
American Woodturner –Winter 1999, pg 26-27
By Jeff Jewitt
The Taunton Press
Tips on finishing with High Performance Polyurethane