2:1 epoxy smoking hot!

hi I been playing around with 2:1 composite resource brand epoxy I picked up at Mitch’s surf shop.   I noticed if I mix smaller batches of the stuff, say about 3 measuring cups worth it works great for dings on my epoxy boards.  But sometimes when I mix larger batches of about half the bottle at once it gets so blistering hot that it starts to smoke and I worry may catch on fire.  I mix it in paper cups and coffee cans .   That can’t be normal can it? I mean how could anyone mix enough to glass an entire board?   Any advice? Thanks.  

Exotherm.  The chemical reaction is moving faster than you are.   You can google exotherm with epoxy to get the detailed explanation.   

When I glass I mix smaller batches, like enough for 1/3 or 1/2 of the board.  I mix it well enough to get a complete mix and then I pour it all out in thin streams all over the portion of the board I’m working on.  Pour all of it out at once. Think in terms of toothpaste-sized ribbons all over your work area.  That way when you’re spreading it you won’t have to move the resin very far.   

I don’t leave it in the mixing cup longer than it takes to mix it and I don’t dump it into large puddles that have to be moved all over my work area.  The less you have to move the resin around to get your coverage the fewer bubbles you’re going to put into your lamination and the less opportunity the resin has to exotherm as a result of sitting together in a large puddle.  

If/when your glassing skills progress that you can finish an entire side with the clean finish in 8 minutes then that’s where the fast and efficient all-pro technique that you see in the vids come into play.  But if you normally move slower like most backyarders (like me) do then it’s smart to change your process to better suit your skill level. 

You might ask if they have a slower Part B that will take longer to set up.   


Mix what you need to use, don’t let it sit in the container. Big containers are better than small ones. Heat doesn’t build as fast. 

Poly will do it too.

The only time I had really bad exotherm was when the resin was old, like 2 years old or more. I use Fiberglass Hawaii Aluzine now and I mix up to 18 oz when I laminate. I often only pour out resin as needed and sometimes I’ll have 4 oz in the container in the container for a while. Once it gets warm enough to notice, I pour it all out. Most people will say to pour it all out, but here in Hawaii the resin is very fluid and will run off the board if I pour out too much and don’t work it around quickly.

I don’t have an air conditioner in my workspace and I work in temps in the 80s.

I don’t seem to do anything normal, but it works for me.

How hot is the room/area you are glassing in?

The only time I’ve had issues with exotherm is when it was over 100F in my glassing tent.

Exotherm is a function of ambient temperature and time.

Especially the amount of time the epoxy is in the bucket.

I have been using that brand epoxy on my last 4-5 boards.

I like it a lot.

Like was stated above, only mix what you need and get it out of the bucket.

Depending on room temperature though, it doesn’t have to be a race.

I’m a mediocre glasser (at best) and I usually glass when my shed is in the 80-85 ish range. Shortboards are no rush. Pour out most of the resin on the flats. Work it around, wetting everything out. Then use what’s extra from the flats and what you left in the bucket to wetout the laps. Tuck laps. Touchups. Walk away.

With epoxy you can pour out on just half the board, say to the stringer line, work it and lap it, then before it sets fully, mix another batch and do the other side.  Splitting the batches will reduce exotherm.  I do this sometimes on longboards.

all the best

Thanks everyone.  I’m using the epoxy to repair delam.  I mix up a batch in a bucket and pour it into a syringe and then shoot it through a pilot hole into the board.  Then I massage it throughout the delam with my hands   and weight to down. Works crazy good with hardly any weight added.  

Well I was fixing a big old delam and mixed up way too much in a bucket at once.  It sat in the bucket a long time through multiple pours into the syringe.  Temp outside was not an issue … like 70’s    Thanks the problem is for sure mixing too much at once, I will make smaller batches.   Agreed that epoxy is great when I mix it correct.  Cheers!

I’ve had problems with exotherm in batches as small as 100g (under 4oz) if I mixed it and left it in the cup. Also if you pour into a fin box and let the puddle sit too long. 


Get it out of the bucket as soon as you’re done mixing.  Lam, hot coat, gloss coat, just dump the epoxy on the board and get to work.