Epoxy overheating during fins installation

Hi, I was trying to install FCS X2 fin plugs and I mixed 2:1 Epoxy with some chopped fibreglass. The solution became too thick to pour into the “H” hole (recommended by FCS) I drilled out. I poured it in anyway, using a stick I pushed the mix into the pockets that was drilled all the way to just below the deck fiberglass. My Epoxy mix hardened so fast that I did not have time to fit the fin plugs in. When I drilled out the hardened epoxy again to salvage the board, I realised that the EPS foam was burnt by the overheating of the Epoxy. My question is, how do you limit the heat to stop Epoxy from burning the foam? Thank you

How long was it from the time you mixed the resin until you discovered it had hardened? Properly mixed, you should have enough working time.

Hello MC-
Sorry to hear of your troubles.
Which epoxy, what density of EPS foam?
Did you preheat the resin side before mixing? Anything more that lukewarm is too warm for a preheat.
Some people use ice packs and multiple pours to minimize epoxy exo-therm that can melt EPS. You could also add some hollow glass spheres to reduce the resin volume in the mix.
My worst time was a combination with .88 PCF (home improvement store) foam, non-standard resin, and off-brand boxes. Now I use better resin, foam, and boxes.

edit: removed brand name reference, it was wrong.

Multiple pours.

Epoxy heats up more when there is a larger volume of it in one place. If you had taken all the epoxy you used and spread it out flat, it wouldn’t have heated up so much… the original FCS plugs with H pattern to the deck is a bad fit for epoxy. The tight route of FCS fusion or futures or basically any other fin install is much better for epoxy…

That said, you can make it work by doing multiple pours. Mix up a little epoxy, mix in your chopped fiberglass, push epoxy mix into hole. But, only allow maybe an 1/8th inch of epoxy to pool at the bottom of the hole. Once that kicks, do another mix and another 1/8th inch, etc, etc, until you fill the hole and s et your plugs… you can put some ice in a ziplock bag and put that over the hole to help keep the epoxy Cool as it kicks and you can probably get away with doing more than 1/8th of an inch of you do this. Still, you’re gonna need to do multiple pours and let them kick in between… since you are doing small batches, you need to be diligent about your epoxy/hardener ratio. It’s easy to be off on small batches… another trick is to mix up epoxy and immediately after mixing, put half of it in a ziplock bag, smooth it all out flat, then put it in the freezer. Use the other half to do your pour. Once that kicks, take the epoxy out of the freezer and use it. This way, you don’t have to mix up such small batches…

Hope this all helps and makes sense…

Hi J,
The resin is resin research 2000CE. EPS foam i got from greenlights starter kit, not sure of density.
I did not pre heat and have no idea what that is and does.
Is Aerosil same as Cabosil? I don’t have cabosil and can’t find it anywhere (living in Singapore), I found Aerosil Fumed silica.
I have q-cell, will it have the same effect as cabosil? Thanks.

Hi Sammy,
It wasn’t long. Less then 5 minuites.

Hi Chrisp,
I got the starter kit and was not really sure which fin system is good for epoxy, thanks for the info.
What i did was take some unwanted fiberglass cut them tiny, mix epoxy with harener, add addetive F and mix somemore, add the chopped fiberglass and mix. The mix of fiberglass made the solution thicker then desired to pour in. Think i put too much fiberglass. What is the percentage of fiberglass to resin mix to make it strong enough but still able to pour? Can i mix epoxy mix with cabosil or q-cell and chopped fiberglass? Thanks

  • 1 what Chrisp said.
    Sounds like you have good materials. Many people who use epoxy are warming up the resin side a bit before use. If you had done this to a point of being too warm to start I could see the works going off before you were ready.
    Fumed silica is a thickener, micro spheres are a filler. Brand names confuse me at times too.
    Pic of my containers:

Not sure of a correct ratio… I usually just mix them up until I get the consistantly I want… it can be pretty thick. It doesn’t need to be pour-able…

Also, what is the air temp when you are doing this? You mentioned Singapore. I imagine it’s pretty warm? Might be a good idea to also set the plugs at night when it’s cool.

Yes you can mix cabosil, chopped fibers and epoxy together. I just add a little at a time untill it’s the right consistency, instead of shooting for a %. Also you don’t need add f for finbox installs. ChrisP is right about multiple pours. I’ve read that higher density (chopped fibers) help with the heat as compared to low density fillers (cabosil). I do big pours of epoxy at work for a completely different application, and after dealing with lots of exotherm problems we do multiple pours and have shied away from cabosil and use more milled fibers now

I like Crisp’s suggestion of putting micro spheres in to reduce the density of the epoxy mix. Use a lot. The epoxy mix only has to be as strong as the foam around it, unless you are doing the old FCS plugs which have to bond to the inside deck of the board. Also as noted above Futures and Fusions need a very slim amount of resin (therefore, low exotherm) so those are best for epoxy.

good luck and all the best

I just tried adding chopped glass fibers on my recent fin plug install, was shocked at how thick and gooey the resin got right away.

I like doing the mix in stages too, I always have problems with bubbles when I try to do it in one step.

Thanks guys
I turned the air conditioning to lowest. Mix epoxy without additive F, add q-cell and fiberglass cloth. Spread the mix on a container with more surface area. I had plenty of time to work as I poured in little at a time. This time it did not burn my foam. All fin plugs are set and waiting to cure. : )

you might still want to put a bag of ice on top.
Extra security.

Glad things worked out, always a good feeling after messing up

Use slow harderner if possible too