Epoxy as clear coat finish over stain?

Hi everyone,

I started planning some details for my DSCM 1q kit (expected to arrive in March) and currently looking into a High-gloss, durable clear finish.

I am planning to use the Crimson stains again on the quilted veneer, but unlike using acrylic clear like last time, I am looking for a more durable finish, as my TLA scratches easily.

1. I know many of you use True-oil, but I read this will cause yellowing, affecting the planned colour?
2. Then a lot seem to use the Cabbots wipe-on or sprayed poly from bunnings. I consider this an option as I think it will be harder than the Acrylic clear, but what is your experience with yellowing?

3. Then there is epoxy: I use the product a lot, and though the formula is tweaked for surfboards, I think it might be great for finishing a guitar, or will it not?
It is hard, polishes up nicely (as long as you can keep the bugs out :D), doesn't require you to wait for over a month to start polishing and I have heaps of it.


Has anyone used epoxy as a finish on a guitar and what have been your experiences?


Thanks in advance!

You want a thin finish on the guitar that’s got a certain amount of flex in it. Too thick and hard, and you end up with guitars with no body resonance that sound dull and flat, like the thick polyester finishes on a lot of guitars of the late 70s to early 80s.

Read any article on luthiers’ opinions on a good finish and they will all say a thin one, generally regardless of the finish used.

So can you get a very thin epoxy finish? Being harder than other finishes, I’d imagine it would ideally need to be thinner than them as well. You can probably easily apply a 1mm thick layer of it, but what about a 0.1mm thick layer? I’m not at all familiar with using epoxy like this, but I’m sure you have a good idea of how easy or hard it would be to achieve.

I don't know what epoxy you are using, but with timber you need to have UV protection. I think just about all epoxies for timber boat building say to overcoat with clear. The Australian Bote Cote epoxy I use has amongst it's range of hardeners a non-yellowing hardener which has UV protection but they still recommend a top coat. They make a 2k water based poly urethane that you use a cross linker rather than the nasty iso cyonate hardeners used in auto urethane . My canoe has had no issues with it. If I didn't have neighbours living cheek to jowl with me I would prefer automotive clear... modern formulations are hard without being brittle and I have the filters for breathable air for my air fed mask. A half mask wont cut it, since the nasties can be absorbed through your eyes.

Thanks for your input,
Really valuable comment regarding the thickness, flex, uv-resistance.

@Simon: Epoxy has more flex than poly, so let's assume that's ok. Regarding the thickness of coats, I can do a batch 'eau bain marie' (warming it in a container in warm water), this will increase the viscosity a lot, which in turn allows for a thinner coat.
All in all after sanding I think the coat will be in the order of 0.1-0.5mm.

What I think will be the most tricky part and perhaps why I will consider going with the poly products is: when you start having fish eyes due to any contamination and you need to sand it back, because it is so hard, it becomes easy to sand through your finish if you know what i mean. And particularly with a carved top like the DSCM this got me slightly worried.


@Rabbit: Thanks for the comments on UV resistance and safety: I added a link to the datasheet if you're interested. All surfboard epoxy's have good flex properties, are more viscose than boat epoxies and have UV protective properties added to them. That being said, they still do yellow over time, but I think not nearly as bad as what I've seen from the tru-oil results. Even one of my 8-year-old boards is mildly yellowish white.
https://www.fibreglass-resin-sales.c...-Surfboard.pdf

I think Simon has a fair point regarding the thickness of application and with that in mind, you cannot beat a spray product. From what I've seen of wipe on poly, it will match epoxy in thickness.

I have no experience with epoxy other using to stick things together, and certainly not as a coating, so can't weigh in on that topic.

However, I will say that if you think you will carry on with this guitar building caper, it could be worth investing in some spray equipment.
You can even get by with an inexpensive airbrush for guitar work. It opens up the possibilities of finish materials, whether you want lacquers or poly, and you're no longer restricted to colour choices on the shelf.

Since you do surfboard building, you may already have a compressor. If so, you're half way there.
I've been spraying my poly exclusively the past few years and it makes a huge difference in the quality of the finish because you can apply a more consistent, controlled layer than wiping on or even a rattle can. IME, the coats can be applied a bit wetter (thus thicker) so you get a quicker build of finish. Even with my cheap eBay airbrush I get better results than I even got with wipe-on or spray can. I mostly use my touch-up size gun now (.08mm nozzle) but the airbrush is still handy.

When it cools off in the Autumn, I plan to spray two previous builds that have hand-applied poly finishes on them.

Quote:

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Originally Posted by RocknRolf

Regarding the thickness of coats, I can do a batch 'eau bain marie' (warming it in a container in warm water), this will increase the viscosity a lot, which in turn allows for a thinner coat.

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Erm, I think you mean make it *less* viscous. The lower the viscosity, the thinner it is. Epoxy can be applied pretty thin. It's a plastic that can ce sanded thin if needed and then buffed up. As a top coat I still think I prefer spraying Urethane, but the epoxy makes a great grain filler! (provided you don't sand through it!)

hahaha, Google, definition: Damn, Less viscous, LESS :D

Thanks for your two cents, good to hear someone who knows both 'products'.

As for urethane: Do you also use the Cabots spray varnish? Link: https://www.bunnings.com.au/cabots-e...B&gclsrc=aw.ds

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Originally Posted by McCreed

I have no experience with epoxy other using to stick things together, and certainly not as a coating, so can't weigh in on that topic.

However, I will say that if you think you will carry on with this guitar building caper, it could be worth investing in some spray equipment.
You can even get by with an inexpensive airbrush for guitar work. It opens up the possibilities of finish materials, whether you want lacquers or poly, and you're no longer restricted to colour choices on the shelf.

Since you do surfboard building, you may already have a compressor. If so, you're half way there.
I've been spraying my poly exclusively the past few years and it makes a huge difference in the quality of the finish because you can apply a more consistent, controlled layer than wiping on or even a rattle can. IME, the coats can be applied a bit wetter (thus thicker) so you get a quicker build of finish. Even with my cheap eBay airbrush I get better results than I even got with wipe-on or spray can. I mostly use my touch-up size gun now (.08mm nozzle) but the airbrush is still handy.

When it cools off in the Autumn, I plan to spray two previous builds that have hand-applied poly finishes on them.

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I'd love a compressor and airbrush, if only I had a shed... At this moment I have nowhere to put all the ideal gear, unfortunately, so have to stay with the strictly necessary gear for now. The airbrush would be a great addition to the finishing options with board building as well so who knows.

But thanks, and yes your finishes are lovely.

Quote:

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Originally Posted by RocknRolf

hahaha, Google, definition: Damn, Less viscous, LESS :D

Thanks for your two cents, good to hear someone who knows both 'products'.

As for urethane: Do you also use the Cabots spray varnish? Link: https://www.bunnings.com.au/cabots-e...B&gclsrc=aw.ds

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Erm, no, I don't use Cabots. I use Aquacote clear https://boatcraft.com.au/Shop/index....dex&cPath=5_38.

I have used epoxy as a finish using Indian ink as a black colour to stain the epoxy. This looks good but I have found it very difficult to get a smooth bubble free finish despite using a heat gun and gas torch to remove bubbles. I also tried epoxy as a clear finish and had the same issues. If you have experience with epoxy you may get better results than me.

Quote:

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Originally Posted by RocknRolf

I'd love a compressor and airbrush, if only I had a shed... At this moment I have nowhere to put all the ideal gear, unfortunately, so have to stay with the strictly necessary gear for now. The airbrush would be a great addition to the finishing options with board building as well so who knows.

But thanks, and yes your finishes are lovely.

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I'm not trying "pressure" you (get it? pressure? air compressor? never mind...:o) but if you don't require a big compressor to run air tools, you can get mini compressors just for airbrushing. You can get decent little unit that will run 23LPI with a nozzle pressure between 10-40 PSI which is heaps for a .5mm airbrush.

Before I got my mini touch-up gun I used a cheap airbrush kit for finish necks and worked great for that. I would have to do more coats (poly) than with the touch-up gun, but the results were good.
Also, with the airbrush set up, you really need a space any different to where you'd use spray cans. I'd be willing to say that there is actually less overspray with the airbrush.

Quote:

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Originally Posted by McCreed

I'm not trying "pressure" you (get it? pressure? air compressor? never mind...:o) but if you don't require a big compressor to run air tools, you can get mini compressors just for airbrushing. You can get decent little unit that will run 23LPI with a nozzle pressure between 10-40 PSI which is heaps for a .5mm airbrush.

Before I got my mini touch-up gun I used a cheap airbrush kit for finish necks and worked great for that. I would have to do more coats (poly) than with the touch-up gun, but the results were good.
Also, with the airbrush set up, you really need a space any different to where you'd use spray cans. I'd be willing to say that there is actually less overspray with the airbrush.

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hahaha, I feel that rabbit 'hole' has found its way to this thread.
Just spent 45mins reading into air compressors, wondering if I could repurpose my tire compressor, and asking myself can't I make a spot for a mini compressor somewhere?

I mean; I do have space, but everything is outside under a cover and corroding away. So I am really looking at solving that before buying more tools.

Anyways, good dreams and will get there. In the meantime I'll keep my eye on gumtree.

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Originally Posted by jimmyedson

I have used epoxy as a finish using Indian ink as a black colour to stain the epoxy. This looks good but I have found it very difficult to get a smooth bubble free finish despite using a heat gun and gas torch to remove bubbles. I also tried epoxy as a clear finish and had the same issues. If you have experience with epoxy you may get better results than me.

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Hi Jimmy,
Did you pour (the epoxy) on receding temps? Sometimes you can do a cheat layer, brushing a really thin layer down, till it gets tacky and then do your coat, this could keep gassing at bay. But really, sometimes you can't help it from happening no matter what you do.

And this has decided me to look at the poly options for now.

Quote:

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Originally Posted by McCreed

I'm not trying "pressure" you (get it? pressure? air compressor? never mind...:o) but if you don't require a big compressor to run air tools, you can get mini compressors just for airbrushing. You can get decent little unit that will run 23LPI with a nozzle pressure between 10-40 PSI which is heaps for a .5mm airbrush.

Before I got my mini touch-up gun I used a cheap airbrush kit for finish necks and worked great for that. I would have to do more coats (poly) than with the touch-up gun, but the results were good.
Also, with the airbrush set up, you really need a space any different to where you'd use spray cans. I'd be willing to say that there is actually less overspray with the airbrush.

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That's good info thanks McCreed. Would you have a link to air brush gun that you would think would work for guitars? Thanks again.

@Rodc - Like anything, you can spend as little or as much as you want. There are mini compressors and airbrushes that cost more than my big compressor and guns, but for a starting reference this compressor ticks a lot of boxes:

Artlogic AC1418

As for airbrushes, that's harder to specify because there are a number of different types, and depend on personal preference.
Such as single or dual action, gravity or suction and nozzle size (some brushes accept various size needles & nozzles, other just one).
You can a cheap $40 off-brand* one from eBay (like me :p) or you can get a $400 Iwata.

My brush is a dual-action with .2/.3/.5mm needles & nozzles, and will do both gravity and suction feed. I have only ever used the .5 nozzle since I have only used it for applying poly.
As far as I can tell, mine is a knock-off of a Sparmax. The biggest issue I've found with the no-name one is spare parts like O-rings, but performance-wise, it's worked great.
I have bought generic O-ring kits that provided the ones I needed, but also gave me ones that don't fit my brush so are of no use. If I had a genuine Sparmax or Iwata I could get full O-ring kits that would purpose fitted.

FWIW the reason I cheaped out on the $40 one was I knew nothing about airbrushing and wasn't sure what results I would get so I minimised my outlay in case it was crap! I would spend more knowing what I know now but I haven't upgraded the airbrush because I bought a mini touch-up gun instead.

*I just checked, and mine branded "Voilamart"

@McCreed, thanks for all this info, really helps!

I could never get nitro to work with my suction airbrush, it just went on very dry and not much of it came out, even if I thinned it a lot. But I think I probably had a 0.3mm nozzle IIRC, the largest that came in the kit, rather than the 0.5mm size McCreed was using. I quickly gave up trying with it and went back to the mini spray gun.

0.8mm with my gravity mini spray gun is fine.

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Originally Posted by Simon Barden

I could never get nitro to work with my suction airbrush, it just went on very dry and not much of it came out, even if I thinned it a lot. But I think I probably had a 0.3mm nozzle IIRC, the largest that came in the kit, rather than the 0.5mm size McCreed was using. I quickly gave up trying with it and went back to the mini spray gun.

0.8mm with my gravity mini spray gun is fine.

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Admittedly, I have not sprayed lacquer with the airbrush, only oil based polyurethane thinned to 60/40 poly/turps.
The nozzle size could definitely be a factor, even only being .2mm difference.
I know modellers spray enamel and lacquer, but that's a very different application compared to guitar finishing.

I also love the .8 mini gun. I don't think I've use the "big" gun since getting the mini.

0.3 and 0.5 are the hole diameters. It’s the area of the hole that changes most, as it’s pi x radius squared, so a 0.5mm nozzle has 4x the area of a 0.3mm nozzle.

I feel an airbrush might work with lacquer with gravity feed, but you don’t get large bottle gravity feed airbrushes, just those small cups. You can get airbrushes that pressurise the suction cup to push the finish out (as well as suck it) and they might work with lacquer or other more viscous finishes. But I’m happy with my mini spray gun and smaller compressor, so I’m not going to buy one on the offchance.

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I feel an airbrush might work with lacquer with gravity feed, but you don’t get large bottle gravity feed airbrushes, just those small cups. You can get airbrushes that pressurise the suction cup to push the finish out (as well as suck it) and they might work with lacquer or other more viscous finishes.

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That's why I got a gun that works with either suction or gravity. You can get jars that are much larger than typical fluid cups. The gravity cup on my unit is 7ml, and the jars (suction) are 22ml. Still not a huge amount of fluid, but you'd be surprised how many coats you can get on a neck with 22ml. Even larger jars/bottles are available, and are made for suction or gravity provided you have an airbrush like mine.

The downside to suction brushes is you need to run higher pressure than a gravity fed brush. Professionally you find that in general, airbrush artists working of hard surfaces use mainly gravity fed brushes, and those working on fabric or canvas mostly gravity fed. The Airbrush artist Mike Lavalee had Iwata make him a 0.3mm brush with a larger cup for less refills doing large surfaces for his true fire. If you are also planning to use an airbrush on your boards and you are selling them, do not get a cheap brush... once you have felt the performance difference of something like an iwata or richpen, you won't want to go back.

I'm something of an epoxy fan, used it a lot for boat building. Not much for my amateur level luthiery though.

There are ultra thin paint on epoxies, and I've used one to stabilise lower quality engineered rosewood fingerboards.

Whilst UV resistance is a huge concern for coatings that live out in the sun, I don't think I'd be particularly worried about guitars that normally live indoors and in cases/bags.

For whatever my opinion is worth though I don't think I'm very enthusiastic about epoxy as a body finish material: I'm a great believer that you should play to a material's strengths, and really decorative clear coating isn't an epoxy strength, unless you're using it to cover an underlying epoxy laminate. So if its a carbon fibre body fine, but I reckon there are better alternatives for wood. I suppose stabilising a really spectacularly unstable spalted or burled finish might be one possibility, but really that's playing to the strength of low shrinkage gap filling adhesive properties.

Jim C

Quote:

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Originally Posted by JimC

I'm something of an epoxy fan, used it a lot for boat building. Not much for my amateur level luthiery though.

There are ultra thin paint on epoxies, and I've used one to stabilise lower quality engineered rosewood fingerboards.

Whilst UV resistance is a huge concern for coatings that live out in the sun, I don't think I'd be particularly worried about guitars that normally live indoors and in cases/bags.

For whatever my opinion is worth though I don't think I'm very enthusiastic about epoxy as a body finish material: I'm a great believer that you should play to a material's strengths, and really decorative clear coating isn't an epoxy strength, unless you're using it to cover an underlying epoxy laminate. So if its a carbon fibre body fine, but I reckon there are better alternatives for wood. I suppose stabilising a really spectacularly unstable spalted or burled finish might be one possibility, but really that's playing to the strength of low shrinkage gap filling adhesive properties.

Jim C

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Thanks Jim, I think you worded it perfectly. After going over all the comments and actually working with epoxy today I realised this too.
There is a lot that can go wrong with epoxy as a top coat and though it is all fixable, I would end up using epoxy just because I already have it and know how to work it. A pretty weak argument if you ask me, also there are far easier products to work with.

So I'm going to do a bit more reading into poly as I think this has the highest chance of a durable finish that doesn't discolour the underlying colours.

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Originally Posted by RocknRolf

So I'm going to do a bit more reading into poly as I think this has the highest chance of a durable finish that doesn't discolour the underlying colours.

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Hehe just make sure it's poly urethane and not poly ester!

Though Fender have used a clear polyester coat over the body as first sealing coat since 1963 (except for all-nitro pre-63 reproductions, custom jobs and some special editions). Clear, and goes over any initial staining applied. UV cured, it sets hard in 15 minutes and is paintable within an hour. It stops any finishes from sinking into the wood and saved them hours in paint and prep work. They've then put nitro or polyurethane or even more polyester over the top of that.

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Originally Posted by Rabbit

Hehe just make sure it's poly urethane and not poly ester!

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Just when you think you have said something funny or outrageous, Simon is on standby to normalise- and flavour it with some history haha

I must admit that I can't but think of thick hard plastic vibration-dulling finishes when I hear the name polyester (as well as some really nasty shirts in the 70s).

Polyester finish is used more widely than you might think, and TTBOMK, polyester is more or less a variant of polyurethane.

It's also worth pointing out that the "poly" that we DIY'ers are buying at the hardware store is very different to what the guitar factories are applying.

Quote:

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Originally Posted by McCreed

TTBOMK, polyester is more or less variant of polyurethane.

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I think you have to me using a *very* wide definition of the word variant for that to be true, they really are rather different, although I suppose there's an argument that one thin coat of polymerised plastic can't be utterly different from another.

Quote:

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Originally Posted by McCreed

@Rodc - Like anything, you can spend as little or as much as you want. There are mini compressors and airbrushes that cost more than my big compressor and guns, but for a starting reference this compressor ticks a lot of boxes:

Artlogic AC1418

As for airbrushes, that's harder to specify because there are a number of different types, and depend on personal preference.
Such as single or dual action, gravity or suction and nozzle size (some brushes accept various size needles & nozzles, other just one).
You can a cheap $40 off-brand* one from eBay (like me :p) or you can get a $400 Iwata.

My brush is a dual-action with .2/.3/.5mm needles & nozzles, and will do both gravity and suction feed. I have only ever used the .5 nozzle since I have only used it for applying poly.
As far as I can tell, mine is a knock-off of a Sparmax. The biggest issue I've found with the no-name one is spare parts like O-rings, but performance-wise, it's worked great.
I have bought generic O-ring kits that provided the ones I needed, but also gave me ones that don't fit my brush so are of no use. If I had a genuine Sparmax or Iwata I could get full O-ring kits that would purpose fitted.

FWIW the reason I cheaped out on the $40 one was I knew nothing about airbrushing and wasn't sure what results I would get so I minimised my outlay in case it was crap! I would spend more knowing what I know now but I haven't upgraded the airbrush because I bought a mini touch-up gun instead.

*I just checked, and mine branded "Voilamart"

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Thank you again for the great info McCreed!