Hot Epoxy - RC Groups
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Feb 23, 2013, 04:08 PM
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Knoll53's Avatar

Hot Epoxy

It's a good thing....Right !

Warm epoxy will flow nicely where cold epoxy is just too sticky and thick to fully wet out the glass. Even more useful when using a device like a tow wetter. But warm does not mean hot.

This morning I was trying out a new tow wetter and recognized that things would be easier if the cold epoxy was a little thinner. Sooooooo, I mixed up a cup of epoxy and put the heat gun to it and stirred until it was runny like maple syrup. Only took a minute on the low setting. Certainly not hot enough to melt or even deform the plastic cup. About 1/2" of epoxy in the bottom of the cup.

Then I got to drawing out the wetted CF tow and draping it on the model. Maybe 5 minutes later the epoxy started foaming and hissing and went off like volcano. It was "insta-cure" epoxy. This is what you don't want. Sound familiar?

2nd batch was with cold epoxy and the wetter worked just as well.

Tow Wetter 2 (0 min 0 sec)

Last edited by Knoll53; Feb 23, 2013 at 04:24 PM.
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Feb 23, 2013, 05:31 PM
Deniable plausibility
Shedofdread's Avatar

I think at one time or another, we've all been introduced to Mr X. O'Therm.... Most annoying when he comes to visit, eh?

Hope you're well and regards from snowy Derbyshire
Feb 23, 2013, 06:00 PM
Live and let Fly !
Lawrence B's Avatar
A long time ago, making boat hulls with polyestor resin i managed to have a small bucket of the stuff smoking thru excess exotherm ... without any external heat !!

Last edited by Lawrence B; Feb 24, 2013 at 05:25 AM. Reason: Poor spelling !
Feb 23, 2013, 11:13 PM
I am actually really slow
Heat gun is to hot, a hot box at 40deg works wonders. I know a guy that used to put resin in the microwave for a couple seconds just to 'kick it off a bit'

Till this day, I am yet to try it. I think its something you do after a couple of beers
Feb 24, 2013, 07:48 AM
chetosmachine's Avatar
Use slower hardener and you can heat the epoxy.
You can also heat only the resin, not the mix. This prevents a bit the exothermic, but it's not magic, it will increase temperature and exo will happen.
Feb 24, 2013, 10:04 AM
Registered User
Heat the resin and hardner bottles in a bucket with hot water from the tap.
15 mins from 55 F get to 80-85 degrees, then mix.
Feb 24, 2013, 04:39 PM
Registered User
T.D.'s Avatar
Yeah, use hot tap water.

Be very careful with a heat gun and epoxy, inhaling the vapour produced can have serious health effects.

Mar 04, 2013, 07:34 PM
Composites guy
Also, heat the tow.
Mar 04, 2013, 08:08 PM
Entropy is happening!
Jim.Thompson's Avatar
Different resins behave differently to each other as well. Some of the better quality low viscosity resins don't need heating to start with, and when/if they are heated, don't exotherm as much and as readily as the cheaper inferior products.
Bit of a catch 22 actually!
Mar 05, 2013, 12:40 PM
Father of Fr3aK, DLG Pilot
tom43004's Avatar
Mixing epoxy in larger batches confines the heat energy from the exotherm and amplifies things. Spreading it thinner or using larger, shallower containers helps slow it down if that's your goal.

I had a quart of West Systems heat up and solidify so fast one time that I dropped the container while I was still mixing it! Most of us have had a bad day due to "premature" exotherm.

Be careful warming stuff to make it flow more easily though. Obviously you shorten the cure time but you could also significantly reduce the physical properties of the finished product when you accelerate the initial cure with heat.

I like to heat up a scrap piece of marble countertop by running it under hot water while I'm mixing the epoxy. When the epoxy is mixed, I pour some of it on the marble and it gets more flowable but still has a large enough surface area to avoid the "flash" cure. The marble is a nice place to pick up epoxy for the roller as well.
Mar 05, 2013, 12:53 PM
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Knoll53's Avatar
Originally Posted by tom43004
Obviously you shorten the cure time but you could also significantly reduce the physical properties of the finished product when you accelerate the initial cure with heat.
I did not know this. Curing concrete has similar problems when it is allowed to dry out too quickly especially right after initial set.

I'm thinking of warming the resin to 80F as a matter of standard practice. Do you have any data showing strength vs initial heating?

Mar 05, 2013, 01:02 PM
Father of Fr3aK, DLG Pilot
tom43004's Avatar
It varies by epoxy Kent. Most of the manufacturers will post a datasheet online.

Here's an interesting full scale link:

and a datasheet on one particular brand:
Mar 05, 2013, 01:27 PM
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Knoll53's Avatar
Thanks Tom. Just the tip of the iceberg for info. on epoxy, I'm sure.

Attached is possibly an easier to download version of the Do and Don'ts Tom just posted.
Mar 13, 2013, 01:53 AM
Registered User
+1 on the warm water bath - keeps the epoxy warm, but stops it overheating too.
standard practice in the boatbuilding industry.

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