Title: The epoxy hardens extremely slowly - what's the cause?
Tags: epoxy
Question: I'm not sure if this is the right section to ask this question, but I assume at least some of you woodworkers have experience with epoxy (Barrikade EP-TP).
I'm having a problem with 2 gallons of epoxy that I bought for a boat building project. I made a test batch and the epoxy is hardening extremely slow. The specifications say the pot time is 22 minutes, but even after 2 hours the batch is still liquid, as if I just mixed it. It takes ~4 hours for it to start turning to gel. After 24 hours it is like soft rubber. After 48 hours it's like hard rubber, but still not hard enough for sanding.
Things I checked and tried:
The ratio is dead on. Specification calls for 100:44, and I'm mixing
16 gram batches with scales accurate down to 0.01 gram.
The ambient temperature is controlled 23 degrees. Specification
calls for 20 degrees for nominal cure, so if anything, the epoxy
should cure faster, not slower.
I suspected that the components have settled too much in their
buckets, so I mixed them before using. Didn't help.
Epoxy was bought 4 months ago, so it's definitely not expired.
Epoxy was always stored indoors, in nominal conditions (never frozen
or anything). No contamination either.
I called the seller, suspecting that maybe he shipped the wrong hardener, but he swore on his mother that everything is correct and the batches are labeled in the factory. He tried to persuade me that what I'm seeing is normal, and refused to send another batch (even if he did want to I would have to wait ~2 months for it, and there is no other epoxy supplier in my country.)
I have a bit of experience with epoxy, yet I've never seen anything like this. What could be the problem? Can somebody please advise?
Comment: I've had a similar experience with regular 5-minute epoxy for woodworking.. JB Weld brand I believe. The hardener was slightly lighter in one package, and it definitely took longer to cure. I didn't use it all at once, so on subsequent applications I used a little more hardener in the mix than predetermined by the double barrel dispenser. Once cured, it felt like the faster -curing mix was actually too brittle. Go figure.

Comment: Well your situation sucks. I would normally say you need to contact the manufacturer in this sort of situation, if the seller isn't willing to help out with what is obviously a faulty product. There are various things you can do to try to diagnose the problem, the most obvious of which is deliberately using more hardener than resin (up to maybe a limit of 2:1). This is not to try to give you a workable product, it only tells you the proportion of hardener chemical in the second container is too low.

Comment: Did you mix the epoxy first time 48 hours ago or will the epoxy never get harder than the hard-rubber stage?

Comment: I tried increasing the amount of hardener, but it doesn't seem to change anything. It has been ~60 hours since the first test batch, and it does seem to be hard now, but, I mean, that's a hell lot of time to harden, isn't it?

Comment: Yes 50-60 hours to cure is totally ridiculous. Definitely something up with the chemistry, which it's likely only the manufacturer (or *a* manufacturer) will be able to tell you about. While it's great that it did finally harden I'd worry that it isn't as strong as it should be. Normally that's not really a major deal but in boatbuilding? I wouldn't want to risk it unless you got assurance from the company that strength won't be compromised.

Comment: I did a useful experiment. I borrowed some epoxy from another boatbuilder (bought from the same source, same manufacturer, same "model", but a year ago), and tested my epoxy and his epoxy side-by-side, as well as mixing my epoxy base with his hardener, and his base with my hardener. 4 batches in total. All 4 batches cure at the same rate, which is extremely slow. So the seller didn't mess up my order. Either this is normal behavior of this epoxy (though specification doesn't agree), or I'm still making some huge mistake.

Comment: Your experiment mirrors my own experience, though I use cheap fiberglass resin rather than a boat builder brand.  I had a year old bucket of resin with a little bottle of hardener taped on top which had been negligently left in my garage all summer.  I knew it had probably gone bad, but kept it around for emergencies.  A month ago, I had an emergency.  I was pouring some newer resin but ran out of hardener.  I used the little bottle from the year old abused batch and the new resin took DAYS to harden.  Hardener aging can cause very slow curing.  Maybe your seller sent you some old stock.

Comment: Since you know another boat builder that uses the same brand and "model" of epoxy you're trying to use, have you talked to him about mixing and cure times to see if he has the same experiences you've had? Even though it seems _very_ odd, maybe that's just how this stuff works.


Here is another answer: I've just checked the website for this epoxy. The pot life is not the same as the curing time.
It states:
Potlife: 30 minutes at 23 ° C
Curing time:  Initial curing 10-12 hours at 23°C. Full cure after 7 days.
So there is nothing wrong here!

Here is another answer: (according to 2019 product data sheet) You actually have your Barrikade EP-TP mixing ratio wrong. is 100:44 BY VOLUME, and if you're doing it by weight, it is 100 : 38,9.
Comment for this answer: Hi , welcome to SE. If you read the Comments above more fully the OP has said he's tried various proportions and cure time remained the same. Also as a general thing, if the amount of hardener should be 38.9 but someone used 44 instead you'd expect *faster* cure, not slower. This may then actually lead to a slightly softer cured product, although I'd expect the difference to be hard to notice from working with other epoxies.

Here is another answer: You will need to experiment. Try ten small batches with increasing amounts of hardener. Check results and repeat based on previous results and go from there. I would look for another product while doing this, though.
Comment for this answer: Thank you for your answer, but everything I've ever read tells to NEVER mess with the epoxy ratio, because there will be leftover chemicals that didn't react. So what would I gain from such experiment?
Comment for this answer: Anyway, I tried 1 batch so far, with 110% hardener. Didn't change anything in what has been 3 hours now. Barely turning into gel, and only now.
Comment for this answer: I think 10 batches is a bit overkill... I'd step up incrementally as you have already done... It looks like you're getting some improvement, down from 4 hrs to 3 until initial gelation/set-up. Continue to monitor progress, and maybe step up to 115-120% hardener.
Comment for this answer: @JR, many companies that make epoxy compounds (not just liquids) are extremely conservative about the ratios, but not all and with some products instructions are provided about how you can play with the ratios for various reasons (e.g. evening up the cure during high and low temps) or to slightly alter the properties of the finished product. For example lowering hardener ratio somewhat paradoxically increases hardness, and upping hardener ratio increases flexibility. I *think* you can use this as a general principle for epoxies, but there's no guarantee it's true for all.
Comment for this answer: I made 4 more batches with varying amounts of hardener. Cure time is the same. I can't speak of the final hardness, as I don't have tools to measure such subtle differences, but I can definitely tell that the epoxy, regardless of the amount of hardener, is still liquid after 2-3 hours.

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