Surface Preparation: Overview
Few things in woodturning can be as vexing as finishing. We all crave finishes that look like glass, or are as smooth as satin sheets and are as luxurious as the feel of supple leather seats in a fine sports car. Creating the perfect finish is a time intensive process that cannot be rushed, or forced. Whilst you might apply a so-called instant finish to a project, it usually loses its luster as fast as it went on. If you want a provocative and sensual finish that begs to be touched, you have to pay the piper.
Surface Preparation: First Steps in Finishing
One of the first steps in applying any finish is proper surface preparation. That means you need to remove any dust or debris (unless you are going for a grain filled type of finish) and clean the surface to remove any oil that may interfere with proper adhesion. This initial surface preparation step is critical to your finishing success, regardless of the finish you choose. Drop the ball here and all of your efforts may be for naught.
You’ve probably heard lots of woodturners say that a finish can make or break a turning… In case you’ve been wondering, it’s true. The finish is the final step in a long series of operations that begin with harvesting the tree and bucking the logs into project blanks, all the way through designing the form, roughing, drying, remounting, finish turning, sanding, finishing and finishing the finish by buffing and waxing. Some parts of this surface preparation process can be nudged one way or the other without significant compromise. Other parts are stubbornly inviolate and are unwilling to yield to improper protocols, shortcuts or impatience. Such is the nature of many modern finishes.
Surface Preparation: Dust and Debris Removal
When finishing my projects, I always prefer to clean the grain pores of all dust and any abrasive sanding residue before applying the finish. The easiest way to do this is with a few shots of compressed air, whilst the piece slowly rotates on the lathe. Next to my lathe, bandsaw and my three chainsaws, the air compressor is one of my most used tools in the studio. A final once over with an air hose is done after the piece is off the lathe, to take care of any dust from final hand sanding (if necessary).
Before I begin to apply any finish, sealer or wax to bare wood, I want to begin with a clean surface. Residual sanding dust can muddy the look of some finishes and will only cause problems if I want a deep, crystal clear grain clarity. In addition to dust removal, compressed air also helps to remove any residual abrasive that may be lingering in the grain pores after sanding. Once the surface of the timber is free of dust, I give the surface a wipe down with a solvent to further clean and visually brighten the surface of the timber.
Surface Preparation: Solvent Cleaning
Solvent cleaning of the surface before finishing is particularly important when working with any timber that contains natural oil like the Dalbergia’s (Rosewoods) and a few other timbers. Residual oil on the surface of the timber can play havoc with many different types of finishes, so it’s always a good idea to remove it as a matter of course before application of your finish. I use several different types of solvents depending on the specific type of timber I’m finishing and the intended function of the piece. These include Acetone, Odorless Mineral Spirits, Denatured Alcohol and Ethyl Alcohol.
Even if the timber you're working with has no natural oil in it (most timber does not contain any oil), a solvent wash can be beneficial before finishing. The reason is simple, once you wipe down the surface with solvent, more dust will come out of the pores. Solvents are also good at removing things like skin oil, perspiration, or the grunge that accumulates on your hands from turning. It just makes sense to clean the surface before finishing! Why risk problems with a finish, when it’s so easy to eliminate problems caused by improperly prepared surfaces?
Another benefit of a solvent wash is that the solvent wets the surface allowing you to see if there are any tiny checks or fissures on the project. If you were a little too aggressive when sanding, or you used your abrasives after they were dull, then heat checking may be evident on the surface. There may also be a tiny check left over from drying that went unnoticed. Once the solvent is on the surface, it will wick into any checks and will appear slightly darker than the surrounding wood. If you notice something that needs attention, it’s much easier to do repair work on bare wood, than wood that has a coat or two of finish on it.
Surface Preparation: Special Concerns for Oily Timbers
Many years ago when I first opened my studio, I also made custom desk accessories for upscale clients. These projects were made from exotic timbers like Cocobolo (Dalbergia Retusa), and other Rosewoods. If you ever worked with these timbers before, you know that they can be quite oily. To remove any surface oils, I used Acetone and applied it three times with three separate folded paper towels (kitchen paper). After the third wiping, I could usually apply my finish once any Acetone on the surface had dried. If the third paper towel were still showing lots of oily residue, I would do a fourth application of Acetone.
This solvent wash proved invaluable to me when finishing these high-end projects and I never had a single finishing problem, even when working on extremely oily timbers like Lignum Vitae and Texas Soapbush. One caveat here: Once you have applied your final solvent wash on the surface, you must begin to apply your finish within 15 -20 minutes, or the oils left deep in the wood may migrate back to the surface.
Surface Preparation: Applying a Sealer
After the surface has been thoroughly cleaned of dust and other residues with compressed air and a solvent wash, I take a good look at the surface under a strong bright light. If I see any areas that need further attention, I address these now before applying any finish. At this point, I decide if I need to apply a surface sealer (not to be confused with a sanding sealer). Primarily, I use sealers with finishes that are built up like an oil finish or a spray lacquer for example.
The reason for this is that some finishes take numerous coats to build up a layer that is thick enough for buffing to create a high gloss lustre. To reduce the amount of finish that’s needed, I pre-seal the timber surface with thin clear lacquer (50% lacquer from can/50% lacquer thinner), or shellac (1/2 lb cut, depending on timber).
For example, I really like Minwax #209 oil finish. It’s very thin however, and it can take 20 – 25 coats (or more) to build up a layer that is acceptable for some projects. Since each layer must be applied once each day, that means that your project is in the finishing room for nearly one month, just building up thin layers of oil/resins on the surface.
If I pre-seal the timber first, I can cut the number of coats down to 12- 15 and get the same result when the piece is buffed. That’s quite a timesaving, with no compromise in visual or tactile quality. Another example is on point here… By applying fewer coats (but with no difference in the end result), you can save quite a bit of money on your finishing products. I really like Liberon Finishing oil as well, but it costs $38.00 per litre (£23.78), so I always pre-seal first to save money and time.
Surface Preparation: Colour Protection
Another benefit to sealing before finishing is that once sealed, darker oil finishes will not compromise the colour of the timber to the extent they would if applied to bare wood. That means that my original timber colours stay truer than if I just applied the oil finish over raw wood. That’s a huge benefit in my book. Some timbers do not need sealing before finishing. I take them on a case-by-case basis.
I would say though that about 85% of all of my projects are sealed before finishing. It saves time, materials and it helps to protect the original colour of the timber. If you are not pre-sealing now, try it on one of your next projects. You will be amazed at the difference and you will get to keep a few more pence in your pocket at the same time to save up for that new gouge, or chuck.
Surface Preparation: Final Thoughts
Finishing is one of the least glamorous parts of woodturning. It takes lots of time and effort and there is little you can do to speed up the process without compromising the final finish. When I was demonstrating on the road a few years ago, finishing was always one of the hot (and most disliked) topics with the thousands of woodturners I met at my turning demonstrations. Finishing is not fun at times for sure, but it can make or break your project and for that reason alone, it deserves your utmost attention. The time you invest in finishing can and does make a difference in how your piece is perceived by the public and collectors.
Safety Note: Be sure to follow all manufacturer’s cautions and safety recommendations when working with solvents in your studio. In the U.S., read the manufacturers MSDS (Material Safety Data Sheets) sheets, in the U.K. read the COSHH (Control of Substances Hazardous to Health) sheets for any solvents you plan to use. Wear all protective equipment that may be required for proper safety.
Safety Note: Always follow all manufacturers safety instructions before working with your lathe, or any of the tools or products you may use. If you are unsure about any operation, obtain competent professional instruction before proceeding. Use and wear all necessary safety devices during turning and observe safe woodturning practices to prevent accident or injury.
Steven D. Russell is a professional studio woodturner, teacher and writer. He has written numerous articles for international woodturning magazines, which have been published in more than 78 countries around the world. Steve has demonstrated in numerous cities across the United States. His studio, Eurowood Werks, specializes in bowls, platters and hollow forms with unique visual and tactile treatments.
Steve is also the current and founding President of the Lone Star Woodturners Association, Inc., an AAW member chapter. The LSWA is a 501(c)3 non-profit educational organization dedicated to teaching and demonstrating the art and craft of woodturning.
Steve is also a featured writer for the Guild of Master Craftsman's "Woodturning" magazine, published in London England. Woodturning magazine is the world's leading magazine for woodturners. Look for his articles covering technical topics, or project based articles in an upcoming issue.