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I recently used some system 3 epoxy, died with some of that black epoxy dye (maybe from Stewmac?) on my fretboard inlays. It seems to be hardening slower than usual. we're at about 24 hours now and it's firm but not so firm that I don't leave fingerprints on it. I've moved the pieces into my furnace room, where the temp is probably about 75.

Does this stuff go bad? I confess that these bottles are probably 2 - 3 years old. Thanks.

I would suspect measuring errors. How do you measure the two parts?

Usually, when the stuff goes bad, the hardener part turns dark and thick.

Thanks - yeah, I've heard that System 3 is very picky about precise measurements. I use a teaspoon to measure - tough to get it perfect, but by scraping out between the mesurements, I think I'm pretty close. Maybe not.

West System sells a small kit for $37 that includes a digital scale good for small quanities. I bought it at a marine store.

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http://www.Harvestmoonguitars.com

DOH! Measure by weight...... Ummm, I already have a digital scale..... yeah, that sounds like a good idea.....

I use those small plastic cups that maybe hold 2 tablespoons all together. I put on my magnifiers & pore the thickest one first & make sure it settles to the line. I sometimes warm the bottles up in a hot tap water bath which makes them less thick. I was told by industrial formulators the stuff last a long time even if they start crystalizing.
MM

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Mike McNerney

I thought the mixing formula was by volume.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Howard, most if not all of the epoxies give measurements by both volume and weight. I've never found West's minipumps to be all that accurate because they tended if you hadn't used them in a while to backflow or air pockets resulting in an imperfect mix. On Wests, the measurements are usually on the hardener label. Not sure where they are on System III but I know Doolin always does it by weight and uses System III epoxies.

Epoxy ratios are expressed both in volumes and weights depending on the manufacturer. Regardless of how it is expressed most epoxies are fairly intolerant of measuring errors. With most industrial epoxies, measuring errors of 5% will result in compromised mechanical properties with a very sharp dropoff in strength when the ratio is botched beyond 10%. For this reason, most industrial epoxies are provided with weight ratios. It may be a good assumption that when you see a weight ratio expressed...it's probably not too forgiving of ratio errors.

Companies that publish one year shelf lives are really covering their buns, given that if they publish mechanical properties for their products then engineers will actually believe them and they'll design dangerous things that are glued together. But there is little to go wrong with epoxy components. If it gets too cold in can crystallize...then you just warm it up. It doesn't suck up moisture anything like urethanes can so that's rarely an issue. It's probably a good idea not to subject it to too much u.v. so store it in the dark.

If you suspect your epoxy...mix up a little and let it cure out. 100% cured epoxy will be too hard to dig your fingernail into unless it was design to be rubbery. None of the things we talk about here are designed to be rubbery that I've heard (Z-poxy, West Sytems...ect.). 100% cured epoxy will have a very smooth, glassy surface. Sometimes a little water will be absorbed by the unmixed components. When that happens water is usually forced out during the cure and will make the cured surface appear a little slimy. Just wipe that off with mek or acetone and look for a smooth, hard surface underneath. If you wipe it off and it's still sticky...you don't have cured epoxy.

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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

With West System epoxy, the ratio is the same by volume or weight. I have had good success weighing it on my digital postal scale.

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John

You are supposed to prime the pumps when you first get them or if they have sat for a while. One stroke on the pump and you are good to go.
I have used the West Systems pumps for 25 years and never had issues with improper mixes. 5 boats, numerous repairs, and hundreds of other projects. Never had a bad mix with the pumps.
L.

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Cut to size.....Beat to fit.....Paint to match.

I have used WEST up to 20 years old, and S3 as old as maybe 5 years. Even when the hardener goes dark it is normally fine. Most epoxies do not mix the same by weight as volume (though WEST does). You can mix them either way but the proportion is not always the same.

For small amounts of either S3 or WEST, I use PD dose syringes. These are sold in drug stores, they are 5cc syringes and the gaskets are O-rings so they are very durable and reusable. Drill a 3mm hole in the cap of your epoxy container, and the syringes will seal perfectly. They also come with rubber bungs that accept the syringes and will mate to many bottles.

One possibly too obvious answer to the hardness problem is that the mix was not properly combined. I assume that isn't it if you have old epoxy, but it is amazing, some people expect a few turns of the stick are all it takes. Another possibility in a larger "well mixed" batch is that the epoxy you actually used was on a stir stick or in a corner, and was simply not well mixed.

Another possibility is that your blacking agent is softening the mix. Certain dyes and even graphite powder can end up delaying hardness though it will usually get there.

Great, feedback, all. Thanks!

Update on the situation is that another 8 hours made a difference. Epoxy had fully hardened, and was suitable for scraping and sanding. I suspect that the blacking agent may have slowed down the hardening process.

Corky, One last thing. It is better to thoroughly mix the epoxy before adding any additives including dies. Not saying you didn't but just a tip.
L.

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Cut to size.....Beat to fit.....Paint to match.

Good thread. I rarely mix more than just a few grams of any epoxy for guitar work. As a result, I just weigh the components accurately on a triple beam balance. That, plus the fact that I mix in a small mixing cup for a minimum of 2 minutes has made a huge difference in the quality and consistency of my epoxy glue ups.

Oh...one more thing...I never use the hardware store epoxy. Instead, I use the good stuff from quality craft stores (Bob Smith Epoxy) sold in smaller quantities. I get similar results with System 3 and West.

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JJ
Napa, CA
http://www.DonohueGuitars.com