Post Class 2: Process Con't

So, how do you finish an acoustic?
This is how I finished mine:

1) Sanding.
Sand like there is no tomorrow in some places and gently in others.
The Spruce top and mahogany neck can be sanded to your heart's content (and should be for a nice smooth finish). I had to sand the top a bit more than I would normally because while playing it the sweat coming off of my arm on the upper bough had stained the guitar top yellow - kind of like the underarms of a white dress shirt. It's not pretty, and it sure ain't dainty but it's the truth and it has to be dealt with.
I sanded it with 80, 150, and finally 220 sand paper to clean up the white top.

I did the same thing for the neck and headstock - being careful not to sand the coin inlay. The copper sands off easily.

The sides and back - being laminate - were similar but not the same. I used 150 and 220 sand paper very sparingly. The instructor said it wasn't that hard to sand through the top laminate to the less pretty layers below. So I went slow and easy. I also used some rounded rubber sanding pads which made all the difference on the sides.

2) Taping
I covered the top of the guitar with newspaper and painters tape to protect it from the stain I was about to apply to the side. Note to self: buy low tack painters tape. Removing the blue tape from the body took some wood fibers with it. Nothing bad but still there.

I also bought some 1/4 inch automotive pinstripe tape from a local AutoZone and used that to mask off all of the plastic binding around the sides of the body. The tape was good to work with but I'm not sure how necessary it was to use it. A few bits of the binding got stained by accident and they cleaned up pretty easy. I could see this being imperative if you used wood binding but in the future if I use plastic again I may try going without - just to see what happens.
In conclusion: I'm glad I taped the top - I have no regrets that I taped the binding.

3) Staining
I had some "Early American" miniwax stain on-hand and decided to use that for the back, sides, and neck of the guitar. No one is going to confuse this guitar with rosewood but it looks less like Mahogany/Sapelle and more like rosewood now than it did before. I'm a fan of both - but if I had my druthers - I would use rosewood every time. I applied the stain with both a brush and a rag. I did two light coats of stain and let it dry overnight. I now wish I had used three coats of stain on the neck but such is life. I decided not to stain the headstock but rather to shellac it (I had plenty left over from my lapsteel build). So, the headstock looks much lighter than the neck, back, and sides.
One Note: once the first coat of stain had dried I lightly sanded the guitar body and neck to smooth out the wood. Staining wood (like wiping water on wood) will raise the grain. By lightly sanding it you smooth everything out again which will make finishing it easier.

4) Filling the pores
Mahogany and Sapelle have big pores. Big enough that if you tried to slather or spray some type of finish on top of them - you would see little pits in the finish. These pits need to be filled. It's best to fill them sooner rather than later.
I chose not to put a sanding sealer between the stained wood and the pore filler. The woodworking gods will probably smite me for hubris but them's the breaks. It is recommended that you do this - put something in between the stained wood and the pore filler. An old fashioned method is to rub on a coat of shellac. Shellac can also add to the luster of the finished guitar. As I'm writing this now - I can't remember why I didn't do this... @#&*!!!!

Ah well. I'm sure it'll be fine.

Just FYI - another option is to spray sanding sealer or a light coat of lacquer to act as a barrier between the wood and the pore filler. So, now that we know what I didn't do - here's what I did do.

I wiped on three coats of clear pore filler. I like clear pore filler for two reasons: You can use it with any wood and it won't bleed color. Having said that - I've never used colored pore filler and other people swear by it.

You wipe on the pore filler, squeegee off any excess, and let it dry. Once it is dry (30 to 60 min) you sand it flush with the body. Note: Another reason to use a sanding sealer of some type between your stained wood and the pore filler - you don't sand through to the unstained wood. Which I did on the neck (hence why I wish I'd used 3 coats). If you are super precise - you can get away with it. I was not super precise and had to 'touch-up' a few areas on the neck and body after I finished pore filling.
Depending on how well you applied, squeegee’d and sanded you may only have to do one or two coats of pore filler. I had to do 3 - so that will tell you how well I did it. But since this was my first go 'round with filling the pores on an acoustic. I feel good about it.

5) Spray Finish
Technically, you don't have to spray. You can wipe on boiled linseed oil or tunge oil or you could do a french polish (20 coats of shellac applied by hand). You have to do something. If you don't protect the wood in some way the oils and dirt from your skin will eventually break down or ruin the wood.

I went with a spray Nitrocellulose Lacquer. Nitrocellulose Lacquer is nasty stuff. It is the definition of V.O.C. But if you wear the correct protective gear (gloves, eye protection, and a respirator) it is easy to work with and gives great results. I don't have a compressor or a spraying rig - so I buy spray cans of Nitrocellulose Lacquer. You can buy them online from Stew Mac or in person at Rockler and Woodcraft.

The great thing about Nitrocellulose is that it partially dissolves the previous layer. So, if you goofed or if the spray can 'spit' you can usually just spray right over it and it will dissolve/cover your mistakes. Also, once a Nitrocellulose Lacquer finish is sanded and polished - it's purdy.

As you can see from the pictures - I had to tape off the fingerboard and the areas where the neck meets the body. I'd like to tell you that it's because I want that wood on wood contact that is going to make all of the Sapelle molecules line up in one harmonious ringing, joyous symphony of sound. But it's really because the guitar fits correctly now. Even a 1/2 a millimeter of thickness will change the fit. I spent too much time fussing over that fit for it to change now. So the neck/body connection doesn't get sprayed.

I taped off the fingerboard and bridge because they don't need to be sprayed. The Rosewood of these parts is so dense it is almost waterproof and can face a life without a finish.
I also filled the soundhole with a crumpled up paper bag. The paper bag will keep any extra spray from coating the inside of the guitar - which doesn't need any nitro and can't be properly sanded/polished anyway.