Use of 2-Part Epoxy on Classical Guitar

Construction and repair of Classical Guitar and related instruments
CarlJones6108
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Use of 2-Part Epoxy on Classical Guitar

Post by CarlJones6108 » Sat Feb 10, 2018 8:48 pm

Hey all.

I'm working on a set of three classical guitars and I'm getting close to where I need to decide on finishes. All three are black walnut back, sides and necks, with WRC tops. I'm considering using epoxy as a sealer. I'm thinking to thin it with alcohol and probably wipe it on, sort of like you would wipe on a thin coat of polyurethane or shellac. Is there any reason not to seal the entire instrument this way, including the WRC top? I won't do the glue surface of the neck or the fingerboard.

Next, I'm thinking to pore-fill the walnut with somewhat thicker applications (two probably or maybe more if needed) of the same epoxy since it is pretty open-pored, with light sanding between as needed. Then finally top coat it with lacquer or polyurethane. I've searched through the forum but haven't found any definitive opinions regarding this type sealer on WRC. Anyone have thoughts and/or experiences?

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by simonm » Sat Feb 10, 2018 11:21 pm

I have never pore filled any top and I have also not heard of anyone pore filling any top. That maybe why your have not found anything.

As far as I can recall the two walnuts I have completed so far (another in progress) have either no pore filling at all or only a small amount of pumicing. I have only once tried epoxy for anything and I found the fumes so bad that I have not tried again. I don't even recall for what I used it but it wasn't pore filling. I have however a batch of 4 walnuts sets that will certainly need filling and I will likely use pumice.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Marcus Dominelli » Sun Feb 11, 2018 2:11 am

CarlJones6108 wrote:
Sat Feb 10, 2018 8:48 pm
Is there any reason not to seal the entire instrument this way, including the WRC top? I won't do the glue surface of the neck or the fingerboard.
Try on a test piece of cedar first, and make sure it's finish sanded the same as your top. You want to make sure that the epoxy does not go blotchy on your cedar.
I did an epoxy pore fill once or twice. I would not do it again, as I thought it was more work than using pumice (although I admit I have got very good it) due to all the sanding back needed. Epoxy is very hard....

You are probably best off to seal the whole guitar with shellac, and then do your epoxy pore fill. Of course, if you thin the epoxy with alcohol, this might affect your shellac sealer, which is of course alcohol soluble. I did not have this problem, as I did not thin my epoxy with anything. Try spreading your epoxy with a credit card (expired one) at full consistency and see if this will work for you, then you can seal with shellac, and then pore fill with the epoxy.
If you sand down to wood after the pore fill, a swipe with shellac should get the color of the surrounding areas back, without leaving a blotch.

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Brian McCombs
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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Brian McCombs » Sun Feb 11, 2018 9:18 pm

Yes you can, but if you do, using too much of it will make you sorry you practiced the skill on a good guitar.
Think very light, very thin and the task requires patience. I think of it as a sealer first...and then a void filler second.

I use Z-poxy a LOT as I like it very much. I apply it to spruce and cedar. I also thin it and paint the inner tuner slots and the end grain of the headstock. In contrast to the rest of the guitar, I apply it and treat it very differently on soundboards. If you get it on the top and it puddles up or shrinks up somewhere into an area that is overly thick, it can make life very difficult for you. It is nearly impossible to sand off a run.

I mix up about 1 fat drop of each part....drip some drops of alcohol into it with a little art brush. Apply a drop to the soundboard and work it in firmly with a couple of fingers, massage it into the wood aggressively. It is a really sweet durable sealer when used this way, its tough and colors/oils don't bleed. You must rub each drop into the wood as best as you can before moving on. It is amazing how far a teeny amount of this can be spread out . You can cover the entire soundboard with only four or five drops. Using your fingers as you would use a rubber while french polishing burnish it into the wood. Wipe it until it gets about as dry as epoxy can feel before it gets real sticky. Then apply another thinned drop and repeat in another area of the soundboard, repeat until the whole soundboard is covered. Your work area needs to be very clean, any sanding dusts or contaminants can stain the epoxy as you rub it in. You should have your bridge footprint masked of course. Cure time a day or two is better, I lightly scuff with 320 and can repeat the process if needed. I like to work it into purling/binding voids a second or even a third time if needed. I will use it to fill rosette voids too. You really don't want to sand through initial coat but if you do, I'm convinced it is the least damaging of the sealers to sand through you can salvage the look with a dab of fresh epoxy, it can sort of heal. I think the softwoods benefit from an epoxy massage....I probably overdo it. It makes for a swell surface to french polish onto. I squeegie three coats onto the back and sides... I paint thinned epoxy onto the neck shaft. It is applied head to toe.

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CarlJones6108
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Re: Use of 2-Part Epoxy on Classical Guitar

Post by CarlJones6108 » Mon Feb 12, 2018 3:15 am

Good info. Thanks. Especially glad you mentioned masking the bridge spot -- I had not given that any thought. Thanks for your insights.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Alan Carruth » Mon Feb 12, 2018 4:31 pm

Be aware that epoxies are all more or less allergenic. It can take some time and exposure before you become sensitized, but once that happens you've got a big problem: the next exposure can kill. Not everybody will be effected, and different brands and types will be more or less sensitizing: you might get away with it, and you might not. Generally speaking the faster the stuff cures the worse it is. I avoid skin contact with any type of epoxy.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by SteveL123 » Mon Feb 12, 2018 4:37 pm

Alan Carruth wrote:
Mon Feb 12, 2018 4:31 pm
Be aware that epoxies are all more or less allergenic. It can take some time and exposure before you become sensitized, but once that happens you've got a big problem: the next exposure can kill. Not everybody will be effected, and different brands and types will be more or less sensitizing: you might get away with it, and you might not. Generally speaking the faster the stuff cures the worse it is. I avoid skin contact with any type of epoxy.
Wow, I have not heard of death from epoxy poisoning before. Do you know anyone who actually died from it?

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by vesa » Mon Feb 12, 2018 6:57 pm

Steve123 wrote:
Wow, I have not heard of death from epoxy poisoning before. Do you know anyone who actually died from it?
What Alan says is serious stuff.
If you are hyperallergic over something you can get an anaphylactic shock and in the worst case it can be lethal, because it can make your tongue to swell, you loose breath, blood pressure goes down etc. etc.
Everything from milk and fish to chemicals can cause it if you have been exposed to.
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Re: Use of 2-Part Epoxy on Classical Guitar

Post by simonm » Mon Feb 12, 2018 7:55 pm

vesa wrote:
Mon Feb 12, 2018 6:57 pm
Steve123 wrote:
Wow, I have not heard of death from epoxy poisoning before. Do you know anyone who actually died from it?
What Alan says is serious stuff.
If you are hyperallergic over something you can get an anaphylactic shock and in the worst case it can be lethal, because it can make your tongue to swell, you loose breath, blood pressure goes down etc. etc.
Everything from milk and fish to chemicals can cause it if you have been exposed to.
Just repeating myself here.
simonm wrote:
Sat Feb 10, 2018 11:21 pm
... I have only once tried epoxy for anything and I found the fumes so bad that I have not tried again. ..

The stuff scared me. Even though I used only a tiny amount I felt bad and was worried that I might get a worse reaction so I decided not to risk it again. Similarly, I avoid WRC.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by johnd » Mon Feb 12, 2018 8:34 pm

Why would you want to use an epoxy? I would think it would hinder the vibration of the top. I don't think it would matter as much on the sides and back.

If you spend a lot of time on building a guitar with the materials nature gave us why ruin it with a man made finish that you have no control over???

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Philosopherguy » Mon Feb 12, 2018 8:46 pm

Yea, epoxy can be nasty stuff. Plenty of boat builders have run into troubles with sensitivity to epoxy. If you are going to use it don't expose your skin to it, and if possible wear a respirator. It is much better to stay away from epoxy if you can. Since it adds nothing to guitar making, why bother? In some fields it is necessary. This is not one of those fields.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Michael.N. » Mon Feb 12, 2018 9:09 pm

I suppose there's always good 'ol shellac.
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Brian McCombs
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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Brian McCombs » Tue Feb 13, 2018 3:49 pm

:D goodness.

Well I'm not sure how its been turned into a tone stealing, guitar ruining, death inducing material.... but if you are experiencing any of those symptoms....Stop, you are using too much.

A one inch drop will cover an entire guitar and 90 percent of it is sanded off. (using proper explosion-proof ventilation, teflon gloves, safety glasses, a respirator and a hazmat suit of course)
When thinned and applied carefully and sparingly, it makes for a very nice sealer. And it works very well for tops, but you have to be very minimalistic about its application. If you slather it onto the top with a squeegee.....you will dislike it very much.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by SteveL123 » Tue Feb 13, 2018 4:18 pm

Brian McCombs wrote:
Sun Feb 11, 2018 9:18 pm
Yes you can, but if you do, using too much of it will make you sorry you practiced the skill on a good guitar.
Think very light, very thin and the task requires patience. I think of it as a sealer first...and then a void filler second.

I use Z-poxy a LOT as I like it very much. I apply it to spruce and cedar. I also thin it and paint the inner tuner slots and the end grain of the headstock. In contrast to the rest of the guitar, I apply it and treat it very differently on soundboards. If you get it on the top and it puddles up or shrinks up somewhere into an area that is overly thick, it can make life very difficult for you. It is nearly impossible to sand off a run.

I mix up about 1 fat drop of each part....drip some drops of alcohol into it with a little art brush. Apply a drop to the soundboard and work it in firmly with a couple of fingers, massage it into the wood aggressively. It is a really sweet durable sealer when used this way, its tough and colors/oils don't bleed. You must rub each drop into the wood as best as you can before moving on. It is amazing how far a teeny amount of this can be spread out . You can cover the entire soundboard with only four or five drops. Using your fingers as you would use a rubber while french polishing burnish it into the wood. Wipe it until it gets about as dry as epoxy can feel before it gets real sticky. Then apply another thinned drop and repeat in another area of the soundboard, repeat until the whole soundboard is covered. Your work area needs to be very clean, any sanding dusts or contaminants can stain the epoxy as you rub it in. You should have your bridge footprint masked of course. Cure time a day or two is better, I lightly scuff with 320 and can repeat the process if needed. I like to work it into purling/binding voids a second or even a third time if needed. I will use it to fill rosette voids too. You really don't want to sand through initial coat but if you do, I'm convinced it is the least damaging of the sealers to sand through you can salvage the look with a dab of fresh epoxy, it can sort of heal. I think the softwoods benefit from an epoxy massage....I probably overdo it. It makes for a swell surface to french polish onto. I squeegie three coats onto the back and sides... I paint thinned epoxy onto the neck shaft. It is applied head to toe.

Image
Very interesting process. Is this your own idea? I suppose the thin epoxy layer offers very good protection against moisture and strengthen the wood.

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Re: Use of 2-Part Epoxy on Classical Guitar

Post by Alan Carruth » Tue Feb 13, 2018 5:57 pm

One account I read, of problems with epoxy, in 'Sport Aviation', the magazine of the Experimental Aircraft Association, involved a person who was building an airplane using fiberglass/epoxy skin over a foam core. He became sensitive part way through the process, in spite of using all the proper protections; mask, suit, etc. He took a couple of weeks off to recover, suited up with special care, and went back to work. Shortly after removing the suit he went into anaphylactic shock and would have died if not for the rapid response of the local ambulance team.

I'll note that it's possible to become allergic to a wide range of things with repeated exposure. My violin making teacher eventually became mildly allergic to both maple and spruce. There are some things that almost everybody is allergic to, such a cockroach parts. That's why some people have a reaction to chocolate: it all has some cockroach parts in it. Better chocolate has less, and almost nobody is allergic to pure chocolate, I'm told.

Once you've become sensitized the amount of material you encounter doesn't matter. What's killing you is the response of your immune system to a perceived, but not real, threat. The hardeners used in epoxies mimic proteins, and that's what makes them sensitizing. I don't think that it requires a large amount of material to become sensitive, either; it's more a matter of persistent exposure over time. Not everybody will react in the same way, of course. Brian has gotten away with it for a long time. You might not. I had a neighbor who smoked cigarettes like a chimney all her life, and made it to almost a hundred. They killed my dad at 67. Statistically smoking is a bad idea, and neither is contact with epoxy that has not fully cured.

In terms of sound, almost any coating will have pretty much the same effect when it's as thin as Brian's epoxy fill. It's a matter of the stiffness and mass that's being added, and we're not looking at much here. Epoxy makes a good sealer in that it should cure reliably on most woods, is tough, has a nice refractive index that helps show the 'light' of the wood, doesn't shrink, and sticks to pretty much anything. There are other coatings that should work about as well, with less risk.

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