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actually with robotics in martin the finish in man hours was drop about 40% finish is about 1/2 the time of making a guitar. I can do a finish in about 6 to 8 man hrs that is from prep sanding to final buff. the first few guitars tool me a lot of time . Once I got the proper equipment and experience your time will drop. this is for Nitro gloss
but it still takes about 4 weeks to do for allowing cure time. In martin and large production shops many have clean rooms and evironmental rooms to aid in curing from weeks to days.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks, Woodie. Do you know that a 4.5 mil coat leaves .41 mil dry from measuring your test sprays?

I ordered the gauge before even finishing your post.


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Those electric film thickness testers underneath that guage seem like the bomb...I was considering one at 2k$...

The best finishing advice I would give to my fellow hobby builders is to "learn to enjoy the work". Finishing takes time, and if you look at it as a chore and try to speed the process, inevitably you will make a mistake in the application or sanding /buffing out.
Good prep work is essential - trying to fill irregularities in the wood with finish is a fool's errand. Being familiar with a finish and it's application requires experience using it. Most finishes have a learning curve and jumping from one finish to another may not allow you to over come it. Finding the process that works for your particular situation and temperament may be something only you can do.
What works for me is to use nitrocellulose lacquer formulated for stringed instruments (piano lacquer is not (a piano is a percussion instrument organologically)). An advantage of this finish is that you can leave it in an all metal spray gun for a week without needing to clean the gun. Spraying the finish only takes a few minutes, but cleaning the gun can take much more time.
I use low cost spray equipment and get the best results by spraying bodies by laying them flat, so I use hot melt glue to glue small blocks of wood in the previously taped off bridge and fingerboard extension area to act as "stand offs". This allows me to spray a full wet coat on the top and a lighter coat on the sides, allow it to flash off, flip the body over and spray a full wet coat on the back and another light coat on the sides, and then allow it to dry. By spraying heavy coats of finish the material has time to flow out better so the limitations of cheap spray equipment (and personal technique ) are somewhat overcome. I tried spraying guitars by hanging them, but found that even using a double coat method I would inevitably get a run somewhere on the piece. Besides being a buzzkill it became a time sink and made sanding between coats necessary.
I have also learned to not rush the finish and only do the sanding and buffing after the finish is completely cured and when I am in the mood to do it in a relaxed manner. Sanding finishes is a lot more enjoyable with a cool drink and tunes on the radio and all the time in the world to do it.
Without a major investment in equipment and experience the amateur luthier is going to require more time to create a finish as good or better than the factories do, so again - learn to enjoy the ride.

That all sounds like good common sense to me, sticking with one finish.
My "spray booth" is horizontal and on wheels so I can get around it in a limited space. The body is on a stick which goes into a section of plastic pipe, so I can rotate it as it flashes off, it helps with heavy coats.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Dry film thickness is the wet film thickness times % solids in the final applied finish...the variable is film thickness, and that is something that just takes practice. On our bridge rout-downs, film thickness (feeler gauge on bare wood bridge patch) has been between 0.004" and 0.005", so assuming some sealer penetration, it looks like we get 0.003"-0.004" dry film...that seems acceptable.

Some good quality stainless shim stock in thousandths increments (18-8 stainless is durable and not too expensive) and consistent routing pattern stock (MDF is amazingly consistent in thickness, but we still check it on all edges) makes this check easier - especially for trim routers without good micro-adjust on depth. A sheet of 0.004" sets us to just kiss the surface at setup, then pull the shim stock for a depth just over 0.004"...scrape to get any last bit of sealer that went deeper. This approach only works for new guitars with undistorted tops - repair work requires a different approach to avoid unnecessary or excess removal of top wood.

An electronic film thickness gauge would be very useful, although a rout-down on a test panel and feeler gauge measurement seems adequate for hobbyist or small shop use. I'm not sure how accurate electronic film thickness measurements on woods like spruce, redwood, and cedar may be, but fingertips do a pretty decent job of detecting very small differences in thickness of adjacent surfaces (e.g., buffed surface and surface of feeler gauge).

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For the times they are a changin'

- Bob Dylan