Epoxy as finish choice?

[kiramdear]

Paul,

Have you ever occasion to use epoxy products in your finishing work? In my boat restoration work I found it an excellent sealer and primer, and a good base for fillers. I've used it also for final clear coating too, and it seems very hard and durable, can be built up quickly and finished out nicely. Its vulnerability to UV is the only disadvantage I found to using it for just about everything I've done with wood, except in a lesser way, its expense and the trouble of mixing. I have no experience with it for fine work, though.

Jes' wonderin' ...

[jingle_jangle]

I use a catalyzing epoxy primer when finishing bike frames, but don't use primers for 99% of my guitar finishes (exceptions are hi-key metallics like Ruby). When I do use primers, I use a polyester primer for surfacing and a urethane sealer as a base for color coats.

I don't use epoxy clearcoats, mostly because it's very time-consuming to level, and I don't have a really good empathy with it--every time I've used it in the past, it's felt, well, wrong. I've never found a transparent epoxy finish that would buff out properly--the heat required to get a shine dulls the epoxy itself.

I don't know of any manufacturers who use epoxy systems for guitars, although some boutique acoustic builders use it.

[kiramdear]

I agree with you that epoxy can't take the heat, but I didn't know if buffing would generate enough to cause problems. And I don't know if you could mitigate the plastickey feeling and still have the mix remain clear. Prolly not.

When thinned, it penetrates and seals pretty well. Full viscosity, I agree, it's hard to get it to lay down the way you want.

I wonder about another application: Can you picture an epoxy & glass/carbonfiber/kevlar laminate acoustic guitar?

[jingle_jangle]

I worked on this one a few years back:

http://www.metacafe.com/watch/763974/co ... er_guitar/

[kiramdear]

That's really cool. No truss rod! And great for a marine environment. I wonder how it sounds.

[teb]

I used epoxy on the top of a cheap mandolin kit that I assembled for my brother, but not as a finish coat. The body was some sort of bland-looking wood and I sprayed the back and sides dark and decided to veneer it on top. I got some nearly paper-thin maple veneer from the Woodcraft store and applied it to bare wood using WEST 105/205 boat epoxy. Once attached, the figure left a fair bit of up and down as the grain wandered around and I decided the stuff was too thin to risk sanding it truly flat without a good chance of going through it in places. I sanded it lightly with a block and then used a stiff squeegee to scrape epoxy into the surface as a grain filler. I'd seen this done on Doolin's website (mid page).
http://www.doolinguitars.com/waterborne ... tions.html

This helped prevent out-gassing (bubbles coming out of the pores) during the epoxy layers that followed. After that cured, I started brushing more coats of 105/205 epoxy on the top surface to build up a bit of thickness. I think I did three or four coats like this, applying the new coats as soon as the one underneath had stiffened enough to not be disturbed by the process. This gets a good chemical bond without prep and allows any amine blush on the surface to float through the new layer to the top. All the epoxy work was done in a single day, with less than an hour between coats. This was then allowed to cure for about three days (sanding green epoxy is bad for you). At that point, it looked like the first photo.

Now I had enough resin thickness to sand the waves in the figured maple top flat without going through the resin. I used a combination of a random orbit sander and a hand-sanding block. I think I took it up to 220 grit. Then the whole body got multiple clearcoats of KTM-9 water-based varnish, top, sides and back and was allowed to harden-up for a week. I don't own a buffer, but I have two arms and once worked hand-sanding big resin castings for a sculptor when I was in college, so I'm not afraid of wet-sanding. I used micro-mesh disks, wet and by hand with a block, started at 320 grit and worked all the way up to 12,000 grit in about a dozen stages. After that, it just needed a bit of polishing compound on a diaper.

The epoxy did it's job of providing thickness without shrinkage. Most epoxy resins aren't as hard or as heat resistant as polyester, so they probably have limited use for guitar stuff. They do, however, stick far better to wood than most polyesters. In the case of things like fingerboard inlays, epoxy is likely to be more stable dimensionally and yield a better bond if it's a hard enough formula to wear well (there are lots of different formulas with vastly different characteristics). The one which looks most interesting to me is probably System3 "Mirror Coat". Excellent clarity, decent hardness and low viscosity for bubble-free fills. In general though, as a finish coat, I don't think you're going to gain anything over the more commonly used finishes and the application techniques needed may be more complex.

[kiramdear]

Thanks, Todd. I hoped you'd see this thread.

[jingle_jangle]

There ya go, boater folk...

I tried the System 3 on an acoustic a couple of years ago, as a grain filler, and was disappointed in its toughness, which in this case was a drawback to good finishing, as time is money. But I know of a number of high-end boutique luthiers who use it as a grain filler, underneath other types of clearcoats.

BTW, Todd...that Teleclonester is a beaut!

[teb]

In my hands, it's more like a weapon of mass destruction. I just don't relate to mandolins, especially those which can be over-driven. My brother is having an octave baritone mandolin built at the moment and I might give that one a try some time. I do kind of like that country-two-tone, saddle-shoe look on the mando-tele though. I've even considered trying something like that when I eventually have my MG 340/12 with the nice figure doublebound. It might be interesting with a MG top and some sort of root-beer sides and back, but I don't know if I'd ever have the nerve to really get it done that way. We would also have to figure out how to break the color by masking at the tailpiece area where there is no binding. At the rate that you guys get booked up though, I imagine I'd have plenty of time to ponder the project.

[jingle_jangle]

Todd, there's nothing to keep you from binding the tailpiece area, too, as long as you're going to be unconventional with a two-toned finish. Consider any bound acoustic with binding all around the top, which is a natural color break.

Binding can be made to curve in any direction, as you know, I'm sure!