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The finish on my OLF Challenge guitar is going to be the new Behlen Gloss Rockhard Table Top Urethane Varnish which I've never used before. Another first for me is a Zpoxy pore fill.

Any reason not to use this combination? Should I put a coat or two of shellac on the top (spruce) like I normally do?

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Steve Smith
"Music is what feelings sound like"

Does this mean nobody has a clue?

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Steve Smith
"Music is what feelings sound like"

I have no direct experience with that finish, but what you're talking about seems pretty normal.
Wash coat shellac, zpoxy, washcoat shellac, finish...,

Actually you can apply zpoxy directly to wood.
So, zpoxy, washcoat shellac, Behlans....

I can only offer my input on the Zpoxy. I used it as a grainfiller on a lacewood topped Telecaster and it worked very well.

Thanks for the input guys. I realize this is a new formulation of the Rockhard Varnish but am hoping it will be the same as the earlier formula as far as application and adhesion. I suppose I will call the manufacturer.

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Steve Smith
"Music is what feelings sound like"

No direct experience, but in boat-building circles(yeah, I got the boat-building bug...), it's always recommended to apply a polyurethane varnish over a epoxy coat(when epoxy is used as a clear topcoat or in fiberglassing) to protect the epoxy from UV, so I would suspect there's no need for the shellac coat between the epoxy and polyurethane...

Test on scrap, first. Toss the piece in the freezer overnight, then warm it quickly, then flash-freeze it again, etc.... You should be able to spot any adhesion issues pretty quickly.

EDIT: since this is a a challenge instrument, and I suspect won't be sold-off when done, why not just leave the epoxy as your final finish? Epoxy buffs-out wonderfully! And instruments aren't left-out in full sun for their entire lives like a boat, so I suspect the UV issue would be moot.

I built a small "computer desk" for my wife a few years ago, and topped it with System three's "Clear Coat" epoxy, and when the surface wasn't as level as I'd hoped for(hey, I'm fussy...), I leveled and buffed it with the same abrasives and compounds I use for my instruments, and it came out beautifully! It's held-up very nicely, too....

Thanks Mario, that sounds like a good way to test the adhesion for sure! I hadn't thought about a plain epoxy finish, I'll have to consider that as well. Guess I'll start testing since I want to start finishing late next week.

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Steve Smith
"Music is what feelings sound like"

Mario - your comment about a buffed epoxy finish caught my eye. Are there reasons epoxy is not commonly used by itself as a finish?

I have some guitars finished with a West Systems epoxy pore fill followed by an automotive urethane topcoat. The adhesion is intense...as good as you could possibly want. I just can't vouch for your urethane varnish having the same properties over Z-poxy. This is the problem you'll always face. Unless someone has experience using the exact same chemistry it's hard to offer advice without feeling uneasy about it....and I'd guess your particular combination is not commonly used.

I think this leads to the point of using test panels. I've done hundreds of tests with various finishing systems. I use the panels not only to practice finishing but also to test impact and adhesion. The impact jig is no more complicated than a long piece of conduit and a heavy metal dowel pin. Letting the pin drop down the tube to impact the test panel on the floor imparts a standardized impact on the panel. From this you can make informed comparisons between finishing systems and get a fairly professional understanding of what works and what doesn't work.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I was assuming (I know, bad thing to do) there would be folks on here who had already used this. As recommended, I will do some testing before I try to finish a guitar with it. My goal with the challenge guitar was to try a number of new techniques but since the I am on a short schedule to get this thing done I guess I will fall back to something I'm already comfortable with. Thanks everyone.

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Steve Smith
"Music is what feelings sound like"

Are there reasons epoxy is not commonly used by itself as a finish?

It can't be sprayed... Other than that(and to some degree, because of it), controlling the final thickness might be a bit tricky.

Excellent idea, the only improvement I could visualize is that instead of a dowel pin, ( which I imagine would impact with a constant diameter, and you would judge the impact by the depth of the indentation ), you could use a metal tube with a ball bearing of slightly greater diameter superglued in the end , and thus you could assess the indentation accurately by measuring the width, instead of the depth, kind of like how the standard Rockwell hardness test works.