If the epoxy stinks its probably bad. It should have a chemical odor that is not very strong, not a smell that will drive you out of the room just by opening the bottle for a few seconds.

I've used a LOT of epoxy and never had any old enough that it smelled that bad, but I have heard of it. Usually when my epoxy's hardener starts to yellow (about 6 months to 1 year old) I quit using that batch for structure and just use it for fuelproofing firewalls. When it starts to be thicker (another 6 months) I toss it.

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I have had 2 hour epoxy that took up to 2 days to quit being tacky... (generally find that I didn;t use as much hardener as i should have when that happens.) I've never had good 5 min or 30 min epoxy that failed to be hard within the list time or double. I've had it set faster (10 min and it was a rock with 30 min epoxy) when mixing a large batch in a warm room.

Never had a problem with Tower brand stuff... I am using some of thier 15 min, 30 min and 2 hour stuff on a plane now.