Acoustic Guitar Construction

I took a two day classical guitar building class with Jeffrey Elliott and his partner Cyndy Burton. http://www.elliottguitars.com/teaching.html The class included a detailed demonstration of how Jeff builds his tops. (more on that later) This post is about the pore fill technique using devcon 5 minute epoxy taught by Cyndy Burton as part of her french polish technique. I admit I would be leery of using 5 minute epoxy, but some of the very best guitarists Julian Bream included are playing guitars finished with this technique and she has been doing it for years. One of the fears Cyndy’s has is that devcon will change the formula.

I have used zpoxy on 5 instruments. Using zpoxy I usually only get one coat on a day, sometimes two. The beauty of her technique was that I was able to completely fill a piece of Indian rosewood in the morning and then sand and seal coat with shellac in the afternoon. (She stated that she usually waits overnight)

I found the devcon easier than zpoxy to push into the pores and it dried clear without the amber tint of zpoxy.

Her schedule was:
to use a French polish muneca to put a good seal coat of shellac on the raw wood. The shellac is carefully applied to avoid spreading color across the wood. She puts the first coats on by striping the wood leaving a gap between strokes and filling in after those strokes dry (just moments). Enough shellac is put on so that there is not wood color being picked up on the muneca on a wipe.

Use a razor blade with the edge ground off (making a mini scraper) to apply and then pull off (you only have about seven minutes!) the epoxy. She uses a very small amount and suggested doing ½ or even a quarter of a back at a time. She also suggested staying with the grain to avoid scratches. One needs to push hard enough getting it off such that you hear the wood. When taking it off, have a rag with alcohol to clean the blade with each scrape. Do it enough to get the epoxy off the surface.

Wait about 10 minutes and a second coat can be applied the same way.

When I tried it the wood was filled at this point but a third coat can be applied if needed.

Let the epoxy cure, probably overnight. We put it in a warm drying box and waited about 4 hours. Level the epoxy with 400P sand paper. Try not to sand through to wood, you can tell if there is color in the sanding dust. (no big deal if you do, the shellac from the FP will cover the sand throughs OK).

At this point you can apply one session of FP. Wait a few hours and start French polishing body coats.
I will try and show this technique on my next guitar.

When I make double or laminated sides, I roll on the West Systems epoxy to get good even coverage.

Would rolling on the devcon be feasible?

The problem when pore filling is not getting it on but getting it off. You really only want it in the pores. I think rolling it on would leave too much on.

Nitro lacquer and other finishes are likely not to be compatible with "Epoxy glue" seems that the shellac will stick to it most times but not always. Put some Devon on a piece of white paper and let it dry --- again most likely you'll see it turns a bright yellow/green in time. I know those that tie flys, for fishing do not use it for this reason. Also I believe Kevininca has an instrument that developed checking after using epoxy glue as a filler -- this did not show up for I believe, months. As one can see my opinion is that I would not take the chance. The formula change is a valid concern too, that product could be made in Kukamunga next week. I make this post not to depute that there have been successes but rather to encourage new comers that after 120 hours plus of work its is best to use a finishing system with components that are deemed to be compatible by the manufactureres of the coatings. I have written documentation that Zpoxy is compaitble with nitro lacquer. And as a side bar, with the dawn of modern coatings -- unless the finish is French polish I no longer use any shellac for a number of reasons.

I would not use it with nitro or any other finish other than a shellac FP. I only french polish my classical guitars. A shellac FP is still highly valued, rightly or wrongly, on a classical guitar, especially the top.

That's good clarification John -- You certainly are correct, not likely that a high value classical guitar can be found without at least French Polish on the sound-board. I really admire a well executed FP finish -- it is a time consuming but very rewarding process.

Ken you remember well. I did 4 instruments using the walmart epoxy, sprayed over with nitro and I think they all have some kind of issue with the finish. Two are in India and the weather is so weird there....high humidity, moisture, hot, that those things might be contributing to what is probably a little separation of the finish over the epoxy. I did not leave a layer of epoxy on the wood, but sanded back to the wood. One is the guitar I play daily and it has some little pin head looking deals going on under the finish. Can't for sure blame it on the epoxy. My last build I used the Hood's and Timbermate (not on the same parts) and both seemed to work very well, although I was not impressed with the Hoods in its ability to fill in two coats as is suggested to not put more than this on. Anyway, I did use the Devcon type and had issues.
No more.
Kevin