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I've been using z-poxy for filler for the last several guitars.... overall, I have been pleased with the results more than paste wood filler...

I have applied three coats to honduras mahogany, the first two came out great,sanded well, powdered-off like usual, but on the last coat, (and after seeing Todd Stock's you tube tutorial), I switched to a squeegee from an old credit card....

this last coat, I thinned with de-natured alcohol ( as I have been doing on the several guitars I used Z-poxy).... the squeegee seemed a big improvement over the credit card application, in that it left no ridge which had to be sanded out...

the problem.... this final coat won't dry... it remains after 4 days, tacky in a few spots..... It is too late now,I can imagine that I should have cleaned the squeegee with alcohol prior to use, and that it may have had some contaminate on the rubber surface...
Any ideas?
Sand out and start over?
Thanks in advance,
jack

No answer here. It is unusual. The only time I had trouble with zpoxy was on a mahog neck when I thinned with DA. But I don't know if that is just a coincidence. I no longer use DA in the mix

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Joe Beaver
Maker of Sawdust

Joe many thanks for the reply

Filippo...I didn't measure... I squeezed out a quarter sized dollop of resin and a quarter sized dollop of hardener, along with maybe 10% denatured alcohol into a small # 3 sized clear plastic cup from the drug store and stirred the mixture with a scrap of wooden binding.... the only difference in the squirt/squirt method I followed on the first two coats, on the third coat, I added the alcohol....
Basically, this is the same way I have done Z-Poxy with the last 8 or 9 guitars, the difference being a new ( non cleaned, straight from the package) 6 inch squeegee on the final coat opposed to an old credit card....

Thanks,
jack

Thank you Filippo

In the West Systems literature, they say to thoroughly mix resin & hardener before adding filler.

I realize that you are not using the same product or adding fillers, but I think the concept still holds - don't get anything in the way when doing the initial mix of resin & hardener. I also let my mix sit for a minute after mixing before adding DA or fillers.

If heat & time doesn't get it to cure, I'd try cleaning it off with DA & a Scotch Brite.

Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Could it be your denatured has too much water in it. I assume you are using denatured that is nearly pure alcohol but that will pick up water if the lid is not fit well or left open. I have not had problems with drying when thinned with denatured but have had problems when my zpoxy gets a little old or the temperature in my shop gets too cold. The fix for me is to bring it into my house and leave it in a warm room (not right by the heater vent also I would not leave an instrument in direct sunlight under any circumstances.

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

Many thanks Kevin and Mike for the suggestions....I have tried hanging the body under my shed next to the shop for a few days, but still there are a couple of tacky spots...I'll probably give it over the weekend and if still tacky I'll try the scotch brite/denatured alcohol to remove it.... thanks again,
jack

Mix your epoxy thoroughly FIRST...then mix in the denatured alcohol. I can't explain why things might have gone well previous to this but mixing the three components together without first mixing parts A & B together DEFINITELY inhibits cross linking. One shouldn't hope to have predictable results doing it that way and no formulator of epoxy is going to say otherwise. For the vast majority of epoxies, non-reactive and reactive diluents are used to adjust the viscosity of a system. The fact that a little denatured alcohol can be used in Zpoxy to thin it without totally wrecking it should be considered a happy coincidence...not a rule of thumb that can be applied to other epoxy systems.

I weigh epoxy with an accurate scale that measures to .1 grams. It would be a good habit to do this regardless of how forgiving the system is designed to be. There is no craftsmanship or guesswork involved with weighing. Zpoxy was designed to mix by eye but if you're going to thin it with denatured alcohol, the ratio of alcohol to epoxy is pretty dicey.

Alcohol in Zpoxy absolutely changes the mechanical properties of the cured material. When measuring small amounts by eye it is quite possible to go well beyond 10% alcohol without realizing it. 20% yields a rubberized film that never hardens although it may sand well enough. Going too far beyond 20% may rubberize it to the point of it being difficult or impossible to sand.

Lastly, because of how the two parts react together to begin the curing process, thorough mixing can't be over emphasized. Mix the two parts WELL before adding the alcohol.

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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

[quote="jackwilliams"]Many thanks Kevin and Mike for the suggestions....I have tried hanging the body under my shed next to the shop for a few days, but still there are a couple of tacky spots...

You need to get that thing in a fairly low humidity 80 degree plus environment for a day or two.

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

+1 on what Zlurgh said

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

As Filippo suggested, I'll do another batch on scrap wood and see if I still have problems...
Many thanks to all the answers and suggestions....
As Stewart said, It's more likely inaccurate measuring and too much ( more than 10%) denatured alcohol that caused my problem...
Thanks again for all the advise and suggestions,
jack

If it's sticky in spots, I'd guess that you didn't stir it thoroughly.

Thanks Jim.... that is certainly a good possibility

I've used a lot of epoxy in the last 30 years or so and have never experienced that it is all that
touchy about mix ratios. Too much catalyst can cause it to cure less hard and too little can cause
increased drying time but it'll eventually cure.

I'll check into buying a digital scale Filippo... thanks for that suggestion...
And Jim... thanks... it's good to know that it'll eventually cure...
jack

A digital scale will work fine. I bought 4 or 5 sleeves of about 50 each of the 1 oz graduated measuring cups a few years ago for around $20. I almost always use those. Just keep in mind that the ratios for weight and volume mixes are usually different so make sure you have the correct one.

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Steve Smith
"Music is what feelings sound like"

Measure the A & B by weight...I always mix 5 grams each for 10 grams total. Then mix it thoroughly. Then zero out the scale with the mixing stick in it and add 1 gram of alcohol.

Note that the A and B components have SLIGHTLY different densities so weighing equal amount of Zpoxy doesn't provide the ABSOLLUTE perfect ratio but it's well within the margins and weighing provides a very consistent result. That's the key to weighing.....consistency.

Experimenting with alcohol ratios, you'll find that increasing the alcohol with Zpoxy yields an increasingly softer rubberized puck of cured material. Not that a little rubberization is going to foil you, but it will at some point, I expect. I got a little scared of using 20% alcohol because of this...but it still sanded fine.

Actually, there could be a case to be made that rubberizing the epoxy under a finish could improve impact strength. It could also be that rubberization could improve adhesion to nitro, maybe even eliminating the need of a shellac binder...or even the sanding of the last wash coat for that matter. The rubberized texture of the cured epoxy could indicate free radicals on the surface, which are typically not found with cured epoxies. Usually, with fully cured epoxy the surface it utterly inert. But if mixing alcohol into Zpoxy leaves a reactive surface it's entirely possible that the bond between the rubberized epoxy and nitro ends up being a molecular bond...and inseparable as a result. I couldn't possibly say this is the case but testing this theory would be easy enough.

Not that I'm ever going to test it. I'm spraying catalyzed polyester for pore filling these days...and loving it. Answer to my prayers....polyester.

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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

Thanks so much for the detailed info Stuart... I really appreciate everybody's help on this issue....jack

According to the info in this thread, I have done everything wrong with Z-poxy and I have had no issues with it curing. Guess I've been lucky.

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http://www.CostaGuitars.com
PMoMC

I've always thought Tony was a bit anomalous.

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Things are getting clearer for me now. Thanks.

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http://www.CostaGuitars.com
PMoMC

I'm afraid to ask in what way is Tony breaking the rules, eventually the conversation will circle around to what he is stirring it with.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Sometimes it's better not to ask

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Steve Smith
"Music is what feelings sound like"

I use the small dosage cups that come with children's medicines. Surely not the most accurate way of measuring, and have not had problems with zpoxy. I did thin it one time with da, even then I just eyeballed the amount. Wondering if its more of a problem mixing thoroughly or what it's being applied to.

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Kyle

Jack,

How did you make out on this? Did it finally dry?

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Joe Beaver
Maker of Sawdust