Finishing Procedures

Finishing Procedures

 Ukulele and guitar finishing procedures appear to frequently involve black art. It’s partly because each luthier has a different vision of the final product and finish companies tend to be secretive about their formulations and changes to same. There is a great deal of emotion and absolutes on the part of individual luthiers about what is the “right” way; I make no such judgments. The following finishing procedure is a blend of the old Martin approach as outlined by Dick Boak for American Lutherie many years ago as well as my own experiences for the shop conditions that I deal with. As such it is simply food for thought and meant to be modifiable for local conditions.

I use an ACCUSPRAY 22sp, a small unit, but more than enough for my needs, since I only spray for 4-5 days at a time every other month. The only problem with the unit is that HVLP air is always coming out of the nozzle, so loose dust in the room is everywhere unless there is adequate cleanliness and exhaust. I spray in a small room, vented to the outside with a Baldor explosion-proof motor, so the spray dust goes outside. The handle becomes unbearably hot after about 7-8 instruments so I wear a cotton glove to deal with that. Discussions with the salesmen suggest that newer models don’t have the same problem, but salesmen always say such things about the model that one doesn’t own yet.

The following advice may be helpful in dealing with mixing and pouring lacquer. Since I dilute my lacquer before spraying, I purchase two additional clean, empty one gallon cans. Wearing a chemical protection mask, I remove the lid from the full can and make a series of “drain-back” holes (with a moderately large nail and hammer) in the groove around the rim that the lip of the lid rests in. This series of holes should be about 1/3 to 1/2 way around the perimeter of the groove. These holes allow the lacquer to easily go back into the can after the pour and not gum up the seating groove. Now take a piece of heavy-duty masking tape 1-2″ wide and half the perimeter of the can long and tape it to the upper edge of the can next to where the holes are so that ~1/2″ of the width of the tape is on the side of the can and the rest is an extension of the side. Now you have a thin but sturdy pouring lip. With newspapers under the two empty cans, pour ~ 1/3 of the lacquer into each of them. At this point you have three cans of lacquer each with a comfortable amount of lacquer in them for adding other ingredients and pouring and in all likelihood, no stress. The hole punching and tape procedures may also be used on the other cans when they are used.

The Finishing Process –

{1} After first sanding the whole instrument with 220 grit Mirka Gold paper and a random orbit sander, I tape off the fretboard and spray a wash coat of M.L. Campbell vinyl sealer. Then I take West Epoxy with finely powdered silica mixed in (West #105 base resin & #206 catalyst), coat the whole body & neck with the epoxy and heat it with a hair dryer on “high hot” to lower the viscosity of the resin for better pore penetration. Alternate heating and hand rubbing into pores for 15 minutes, followed by removal of the excess resin with a plastic scraper like a credit card (my unused American Express platinum card does a good job) and wiping dry with paper towels works well for a large-pored wood like koa. Smaller pored woods might respond well to lesser treatments. I wear a chemical filter mask and two (2) pairs of vinyl gloves for the massaging in procedure because of the toxicity of the resin. The next day when the epoxy is hard, I re-sand with 220 grit Mirka paper & random orbit sander after removing fretboard tape, then retape the fretboard for the actual sealer spray.

{2} Spray 4 coats M.L.Campbell high-build lacquer at 45 minute intervals. Lacquer diluted as follows: sealer 50%, lacquer thinner 30%, BASF R-M Alpha-Cryl #883 retarder 20% & spritz of fisheye killer. Next day sand with random orbit sander and 220 grit Mirka sandpaper. The random Orbit Sander must be slowed down with router speed control or powerstat until you have reached that point at which the sanding paper will not clog so readily. A great tip from Steve Grimes of Grimes Guitars on Maui is to affix one of those coarse, natural-bristle brushes bristle-side-up to the workbench and touch the film disc to the bristles while the sander is still running. It works great to remove the little toodies of lacquer that prevent the paper from actually touching the surface to be sanded and of course makes the paper last much longer.

{3} Then spray 2 coats M.L.Campbell High-Build Nitrocellulose lacquer diluted like sealer above at 45 minute intervals. Next day sand with 220 grit. Repeat spraying and sanding process until satisfactory leveling has occurred (usually around 10-12 total coats). Now spray just one coat of lacquer and let sit for a week. Sand with 3M 1000 or 1200 grit.

{4} Buff with Meguiars yellow plastic foam buffer on drill press or hand drill or flex shaft and 3M Finesse-It buffing compound at about 1200 rpm. The yellow foam pad begins life looking somewhat like a Camembert cheese, but must be reshaped with a wood rasp on the drill press so that the upper half is concave rather than convex. That way, areas around the neck joint can be more easily buffed. I’ve also made a smaller buffer by taking a portion of the yellow foam pad and gluing it to the bottom of 1/2 of a home made violin clamp. The threaded end of the violin clamp then fits into a drill press or flex shaft to make buffing smaller areas more easy. A picture of same will appear shortly. Optional wax with Meguiars #16 car wax (no silicones).

This finish is orange peel-free, not satin, not wet glossy, but deep and non-intrusive. Much, much work but worth it. E-mail if questions arise…

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