Epoxy curing extremely slowly

Hey guys, I'm back to boatbuilding, I'm having a problem with 2 gallons of epoxy that I bought for a new 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:

1. 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.
2. 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.
3. I suspected that the components have settled too much in their buckets, so I mixed them before using. Didn't help.
4. Epoxy was bought 4 months ago, so it's definitely not expired.
5. 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?
P.S. The brand of the epoxy is Barrikade EP-TP, made in Norway.

 

Hello Laukejas,

A good thing that you made a test !
If you had the temperature and mix (weight) ratio correct there's not much you can do but not use this epoxy.

Only thing that puzzles me a bit is your "16 gram batches". What do you mean by that ? Did you use 6.25 x 16 gram resin and 2.5 x 16 gram hardener ?
Wrong mixing ratio is the main reason for epoxy problems (or so the internet says...).
Could it be you have mistakingly mixed the wrong ratio ?

Good luck, Hans

 

Hey, Hans, thank you for for replying! By 16 g, I meant 10 g of epoxy, 4.4 g of hardener, plus 2.2 g cup, so 16.6 g in total, to be precise So I'm sure the ratios are correct.

As for not using this epoxy, well, I don't have any alternatives, it's the only supplier left in my country. Besides, other people used this epoxy without problems.

 

16 / 144 * 100 = 11.11 grams resin

16 / 144 * 44 = 4.89 grams hardener.

These batches are very tiny.

It might be very hard to properly mix.

How are you doing it?

 

Maybe you can borrow some resin and hardener from "the other people" (other boat building enthousiast you know ?) and mix them with your resin cq. hardener, see wich one is at fault ? Then you would have a good position to claim a good one from your supplier.
Cheers, Hans

 

See my reply above about the amounts I use. Yes, it's tiny, but I used batches much smaller before without problems, always cured correctly. I do it in a small disposable plastic cup, mixing with small wooden ice cream holder.

 

For batches this small; you have to take into consideration stuff sticking to the cup and the stir stick.

I think you ought to test a volumetric test (2:1) and use a larger amount to see what happens.

 

You can also weigh your volumetric test to see if 100:44 is accurate.

 

Make sure and add the resin first. If you make this small batch and the hardener sticks to cup edges a bit; you'll be off as well.

 

It is better to err on the side of more hardener.

If you used a new wood spoon; even the spoon would use some product.

I would purposely test with a higher hardener ratio than spec as well. Use say 120% hardener to see the outcome.

If you find the right number; you could ask for some more from the vendor or course of action.

 

Hans, thank you, I will try to make test batches with borrowed epoxy.

Fallguy, I used to make batches as small as 2 grams, dozens of times, and never had problems with keeping the right ratio. I can make a volumetric test like you suggested, but I doubt it will reveal much...

 

You can test the weights without even mixing!

 

It seems relatively, though not absolutely, clear that the hardener amount is off.

Exactly how is unknown.

 

I did the volumetric test, and it appears that the weights are correct (matching specification).

I also borrowed the same EP-TP epoxy from a fellow boatbuilder, which he bought a year ago. Then I made 4 batches:

1. My epoxy
2. Borrowed epoxy
3. My A + borrowed B
4. My B + borrowed A.

It has been an hour in 22° C since I mixed all four batches. All of them are equally liquid, not even close to turning into gel. I can' tell any difference in viscocity. Does this mean this epoxy is behaving like it should? My first batch (made 3 days ago) was still runny after 3 hours, even though specification says pot life is 22 minutes. How is this possible?

Important note I forgot to mention: I checked my scales against 2 other scales and a known weight. Scales are accurate.

Now I'm totally out of ideas...

 

Could it be that the surface/volume ratio in such a small batch is much higher than with a "normal" batch size? That might increase the cooling effect to the extent that the reaction temperature becomes too low (since all specimen are affected)? How about testing in the oven at, say 40 C?