Finishing Turned Work – What I Do

1. Introduction

I must have tried at least a dozen different finishes but I have yet to find the “perfect finish”. Every finish presents the turner with a mix of pluses and minuses. Crafting a polished, durable finish means understanding and working with those tradeoffs. In my time as a member of GWG, there have been more presentations on the topic of finishing than just about any other I can think of. Yet, I hear comments from members at nearly every meeting that they just can’t get a good quality finish on their pieces. The reality is that achieving a good quality finish is not difficult, but it can be time-intensive. On my projects, I usually spend more time on finishing than I do making chips. Anybody who thinks that a good quality finish is achieved by simply brushing/wiping/spraying some magic stuff from a can is kidding himself.

1.1. Why bother with any finish?

Many wood species, once well sanded and burnished, look good with no applied finish. Unfortunately, beautiful grain color and pattern may be transient. Many species will fade in a few months. It will happen whether the piece is finished or not, although a finish slows down the rate. Some species darken (e.g., cocobolo, and padouk) and some others will lighten (e.g., walnut), but that eye-catching beautiful grain pattern may be transient regardless of the finish. If a finished piece gets dinged, repairing the finish can be a chore. So why bother? I apply a finish for these reasons:

Increases eye-appeal
A well-polished surface invites the viewer to take a closer look and maybe even touch the piece, thus inviting a closer relationship between the two.
Provides the piece with sufficient protection to allow limited handling and cleaning.

1.2. Choosing a finish

Characteristics of finishes that influence a turner’s selection:

Ease of application - Spray, wipe, or brush. Each has its own set of cleanup issues. I prefer to wipe (or sometimes brush) on my finishes. I share my shop with my wife’s car, so over-spray is a significant consideration for me.
Drying vapors – Some finishes give off unpleasant vapors in drying. Consider ventilation needs.
Appearance -

Clarity - flat and semi-gloss finishes achieve their properties by having varying amounts of diatomaceous earth stirred in. Some people claim this can cloud the finishes final appearance. I’m not convinced, and I like the appearance of a polished semi-gloss finish. I think it looks classy. The quality I look for is a softly polished sheen- not a flat finish, and not a highly polished, plastic-looking finish.
Tint - Some amber-tinted finishes can slightly darken the appearance of a piece. I mostly use clear finishes.

Durability - Resistance to scratches, wear, chemical resistance (including fingerprints).
Distortion - Water vapor resistance (may be significant for lidded vessels and segmented turnings)
Ease of repair - The inevitable “oops” can happen without warning.

1.3. Finish types:

A presentation of the features of various specific finishes was made last year and is posted on the GWG website, so I won’t repeat it here. I want to talk about the finish I use for most of my pieces and the series of steps I go through to apply it.

2. What I do

2.1. Surface preparation.

Achieving a quality finish begins with a good foundation- prepare the surface properly. Finishes emphasize surface defects. So tool marks, end-grain tear out, sanding scratches, dents must be eliminated before applying any finish. At show & tell sessions at just about every meeting, I see turnings that have not sufficiently resolved those issues. The level of quality depends on the piece’s intended usage and your sense of craftsmanship. A high quality finish will demand more time, but your satisfaction will be greater.

Work to the best tool finish (Step 1) you can and then transition to sandpaper (Step 2). Progress through the sanding grits from course to fine. Most quality finishes require sanding to at least 400-grit. You’ve heard all that before. But on your next project, consider these thoughts:

Try sanding successive grits in perpendicular directions such that the final grit is in the same direction as the wood grain. You’ll find that’s a lot easier to see when the piece is ready to progress to the next finer grit. In deciding whether to proceed to the next finer grit, use a bright light held at a low angle to the work piece. Sanding scratches show up much better in that light than direct overhead lighting. Use compressed air to remove dust from the piece. Look closely at the surface. If you see perpendicular sanding scratches, you’re not yet ready for the next finer grit.
Slow down the lathe speed to about half of what you used for cutting with a gouge. Sanding works better at slower turning speeds. You’ll get a lot less heat build-up.
Understand the different grit scales (see grit chart), what a grit size means, and what grit ranges are appropriate for woodworking. For example, 400-grit sandpaper has a mean grit size of less than .001 inch. So 400-grit sandpaper is putting scratches into your piece that are on the order of less than .0005 inch. For reference, a sheet of regular copier bond paper is about .003 inch thick. A piece of finished wood that shows 400-grit scratches is unusual.

2.2. Applying the finish

The following assumes we’re interested in a built-up film finish that can be leveled and buffed. It assumes the intended function of the finished piece is decorative, non-utilitarian, and the piece will not get wet. It also assumes a wipe/brush-on finish (not sprayed). If a piece has some surface defects that need to be filled, I like to save some of the dust from the sanding step and mix it with epoxy to form a paste that can be used to fill the defect. Choose an epoxy that is clear and has a working pot life of enough time so you can work with it. The brand I like is the West System that is often advertised in the back advertising section of Fine Woodworking. It’s also usually available at nautical supply companies. Once the epoxy has cured and is sanded to contour, it will require a close examination to see it.

Before applying any finish, use compressed air to blow all loose dust off of the piece. Clean the shop area. Allow dust suspended in the air to settle out. Throughout the finishing process, limit other activity in the shop that might cause dust to get into the air.

Step 3

You’ll need a bottle of thin CA glue (aka cyanoacrylate, aka super glue) and disposable gloves. I like the latex kind. Do this step in a well-ventilated area. Having a small fan behind you to blow vapors away from you is a help. Working a few square inches at a time, apply a thin coat of the CA glue to the surface. If your work piece has some natural edges, I recommend being careful to not get CA onto those surfaces- it’s hard to get off. Work quickly and cover the complete surface. Wait about an hour and repeat the application. That should be enough so that the wood will no longer absorb more CA into its fibers.

Step 4

Sand the CA back down to the wood surface with the same grit size you used last on the piece. What you have now is a hard, thin shell of CA glue penetrated all around the surface of the piece. That shell has uniform density, hardness and depth, and the CA’s clear color won’t impact the color of the piece. With the transparency of the CA, it can be hard to know when you’ve gotten down to the wood surface. A high-intensity light held at a low angle helps.

Step 5

Use compressed air to blow off loose dust. Wipe on lacquer. I like to use disposable gloves and little 2”x2” pieces of cotton cloth patch cut up from old T-shirts. After each coat of lacquer, clean up is as simple as throwing away the glove and cloth patch. I turn my lathe down to rotisserie speed. Wipe on a uniform thickness coat of lacquer and let the lathe run slowly for about an hour to be sure no sags or drips develop. Wipe on a second coat once the first is dry. Relatively thick coats are OK. One of the advantages of lacquer is that each coat dissolves into the previous coat, leaving no “ghost line” between the layers.

Step 6

Once the second coat is fully dried, use 400-grit sandpaper to level the outer surface. This removes any dust nibs or drips or sags. Use compressed air to remove loose dust. Apply another coat of lacquer. Once it’s fully dried, level with 400-grit sandpaper. Blow off loose dust. Repeat as many times as you want, but I use a minimum of 4 coats. For the final coat, I’m especially careful to be sure the work area is clean and there are no sags or drips in the coat. Allow at least a day of drying time before trying to level it. After the last coat has been leveled, burnish with a fine Scotchbrite pad (the gray-colored type).

Step 7

Buff with a soft cotton wheel and white diamond compound (Tripoli also works, but cuts more aggressively, so there is increased risk of cutting through the finish to bare wood). Apply a carnuba paste wax coat and buff vigorously with an old, clean towel. Turning the lathe speed back up again helps. You may want to apply a couple coats of paste wax.

References:

1. Fine Woodworking Magazine, No, 168 (Feb04), page 39.

2. Flexner, Bob, Understanding Wood Finishing

3. GWG’s website. There are several articles on finishing tips.