I have some epoxy still in the bottle that is several years old, and the hardner seems to have yellowed. Is this a problem?

I tested it on some scrap balsa pieces and it seemed fine, but I'm about ready to assemble a tail section and I don't want to take any chances.

Also, although 30 minute has a longer curing time than the 15 or 5, is it any stronger of a bond, or are they all the same strength?

Thank you!

I can only tell you what I've read:

According to one of the manufacturers (ZAP, I think - Tiano?), epoxy does not go bad. What it does do, however, is get thick (crystalize)? If it does get thick, heating it in the microwave for 10 seconds or so will get it back to a liquid state.

I also understand that 30 minute is stronger than 5 minute - mainly because it soaks further into the surfaces being glued.

RCPAUL

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<hr>I tested it on some scrap balsa pieces and it seemed fine<hr></blockquote>

In my opinion, you did exactly the right thing here. I use old epoxy all the time but test it first, just as you did. Never had a failure.
I also agree with RC Paul and just read the thing about the crystalization recently, but can't remember where.

Thanks for the info!

In addition to being able to soak into the wood better, epoxies that take longer to cure are also stronger. Yes, 5-minute epoxy has the advantage of a quick cure time, but it's more brittle than epoxies that take 30 or more minutes to cure.

Just my $.02

Bob

You can remove crystals by placing it in hot water 180 degrees and allowing it to stand. The crystals (if any) will go back into solution.

Heating in the microwave can do all kinds of things from rupturing the container to melting the container and having a real MAD wife..

vettdvr

JAMES, thanks for the advice. We gotta keep the stewardess happy, or else look for another hangar[img]i/expressions/face-icon-small-smile.gif[/img]