Brian's Guitar from Conception to Birth or How to Build a Guitar in 62 Easy Steps!
50 The Seal Coats
The purposes of applying sealing coats are twofold. First, you want to fill in any open pours in the grain so that the lacquer which we’ll be applying next will lay down perfect and smooth. Second, lacquer thinner is more or less toxic and it will eat through just about anything, except shellac. The shellac will seal our previous work and protect it from any funky chemical reactions we might get from applying the lacquer directly over the dye and oil. You can buy premixed shellac, but I prefer to make my own by dissolving shellac flakes in denatured alcohol. This way I can control the color and concentration. Shellac flakes come in several colors: blonde, orange, and garnet. Blonde is very pale and garnet is pretty dark. We chose the middle tone, orange, to layer on more of the amber tones. The layering of colors will reflect light differently emphasizing the three dimensional figure of the wood. The surface of the guitar will appear to move as you walk past, kind of like a hologram. I will make what is called a two pound cut mixture which is basically just an average concentration of flakes to solvent. When it’s applied, the solvent will evaporate off leaving the little dissolved shellac bits behind. The directions on the can of shellac flakes said for a two pound cut, mix 2 ounces of flakes with 8 ounces of denatured alcohol. Dump them both into an old jar (in our case, a Frontera Chipotle Salsa vessel, excellent flavor) and shake them up. Let it sit overnight and shake it some more. It should completely dissolve in about 24 hours. This should make enough shellac for the four coats we’ll be applying.
Prepare the surface of the wood by throughly wiping it with a tack cloth to remove any dust. Make sure all of your little holes and penetrations are filled so they’re not clogged by the following coats which will be built up. For holes too small for wadded up tape, try some small screws. To get an even coat, you will have to spray-apply everything from here on out. There is no way you can brush or wipe it on and have it look good. To remove any undissolved shellac flakes, strain your mixture through a disposable paper filter-funnel or an old T-shirt into your spray gun’s reservoir. Now for a few comments on spraying technique: ● Please spray in a well ventilated area, your garage, or outside in the shade somewhere. I wrapped a corner of the basement off with plastic sheeting. If possible, spray in an area other than your woodworking shop to cut down on any stray dust getting on your finish. ● Please wear a good respirator; a cloth dust mask will not do. Just think about it, shellac and lacquer are specifically designed to stick to anything and dry hard. That includes your nose, throat, and lungs. The first time a sprayed something, I did not use a respirator. The next day I was sick and blowing chunks of stain filled mucus out my nose. Don’t learn the hard way. ● The solvents used (alcohol and lacquer thinner) are not only flammable, but in a sprayed state, they are combustible and explosive. Don’t spray near an open flame (like a cigarette or a pilot light). ● Test your setup on a piece of scrap wood. Make any adjustments to your gun before you start messing up your guitar. Get a feel for the amount of spray and the speed you will need to be moving. ● Be patient! Runs, drips, and sags are bad. If you make any, you will have to completely sand them out and start over. Don’t try to rush things or all of your hard woodwork will look like crap. ● Start the gun moving before you pull the trigger. Start spraying outside your piece and continue past your piece before releasing the trigger. This constitutes one spray “stroke”. ● I prefer to hold the guitar while spraying. This lets me keep the gun relatively level the whole time so that my finish doesn’t leak or drip on the surface. Do whatever works best for you. ● Try to keep the spray perpendicular to the piece and the same distance from your piece throughout your spray. This will provide an even distribution of material. Move quickly to avoid throwing too much finish in one spot. ● Each stroke should overlap the previous one going back and forth. It should take about five “strokes” to cover one face of the guitar. These five or so “strokes” constitutes one “pass”. ● On the same side of the guitar, make another “pass” at 90 degrees to the first. I’ll call these two “passes” one “coat”. The surface should just be wet and thoroughly covered. Any more would start to drip, run, and sag, which would be bad. ● Repeat the procedure on the other side of the guitar. Don’t forget the sides of the guitar, the headstock, the control cavity cover, and the truss rod cover. ● Hang the guitar to dry. Nothing fancy here; I used a wire coat hanger hooked through a tuning peg hole secured to a floor joist above with an eye-hook. ● Clean your gun at the end of each day’s spraying. Schedule for applying the shellac coats: ● Spray on one coat and let the guitar dry for at least one hour. ● Spray on a second coat and let it dry overnight. ● Repeat the process the next day for two more coats (making a total of four coats). ● Depending on your personal schedule, you can always wait longer. Just don’t spray any sooner or the previous coat may not be fully cured. ● The next day, lightly sand the surface as explained in the next step.