A Note On The Polyester Resin Curing Process

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BFDesigns

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So I was slush casting the inside of a skull prop to reinforce it when I go to make a sand mold of it to blow glass into sometime later today. And to make sure that the resin would cure all the way, I used a lot more hardener than I should've.

I filled up one of those little mix trays that comes with the quart sized resin can with resin. I think it may hold something like 6 oz tops. At 7 drops/oz to cure properly it should've taken me only 42 drops total each time I needed to mix up a full tray (I mixed 5 and I still need more!). Anyway, instead of using the directed 42 drops, I used 60 in each tray. The good news is that the resin sets within 7-10 minutes with this mix time. The bad news is that as it catalyzes it generates an insane amount of heat!

Now when we go to paint the fiberglass layer on the insides of our armor usually the temperature reaches somewhere between 100°F-110°F tops. This mixture with the 60 drop ratio (~1-1/2 times the normal dose) reached its peak at somewhere between 150°F-180°F! I don't know what the flashpoint of Ester resin is but I probably came dangerously close to achieving it with this round and I also came pretty close to burning my hand when I picked it up to check the status of the resin. I actually could not hold it in my hand as it was too damn hot! The heat has since dissipated to about the normal curing temperature of 105°F now but it has taken almost half an hour to sink that much heat off of it.

So remember kids that when you're playing with resins or casting with them, read the damn directions so you don't end up setting your project/apartment on fire! And if you do notice that the generated heat is becoming insane and too hot to handle, pop it in the fridge for a minute or so and watch it.
 
Might not be a good idea to put this stuff around any food you plan on eating. Fumes, residue and the such.

Man, how much would that suck for your helmet, which you've worked so hard on, to spontaneously combust right in your hands. :D :eek:
 
I've done the same thing a few times, I've never had any accidents, but you're right it sure gets hot!

Thanks for thinking of our safety.

Good luck with your glass skulls. Makes me miss my days doing glassblowing in college. Plaster/silica makes a nice blow mold too, with a little graphite on the surface.

Cheers,

-Sean
 
I've done this several times, when I was doing some boat repairs. Too much hardener does two things: obviously, it heats the part up. Alot. I've seen full containers of resin mixed up by people who had no idea what they were doing, and catch fire... To the point of throwing it in a pail of water and it exploding from the thermal shock.
It'll also make the resin incredibly brittle. I'll mix hot, sure, but I've seen boats and car repairs where the resin was mixed so hot its almost chalky.
Two things affect the speed at which resin cures: ambient air temp and humidity. Living in Arizona, at 6:00 in the morning, in the middle of july, it'd be 80 degrees. and in the hour that it took to get everything prepped, mixed and applied, it'd shoot up 10 degrees if not more. Meaning the mix I just made for 80 degree air temp was already too hot before it even started to cure. Of course it'd hit 110 bit 9:30-ish.
God I hated Arizona. I got more thermal and chemical burns there, in 2 years, than I have in the 15+ years I've been doing this. :oops:
 
I believe it is best to use 1% Catalyst - no more, no less. Too little catalyst could be a bigger problem. :rolleyes

- Dan
 
This same safety rule is applicable to Bondo as well, you should always be trying to do this sort of stuff in the shade and not near anything flammable.
 
It's a good way to make the flaming Hayabusa helmet. :p

When I tried casting straight from pep the first time, the resin managed to melt the latex gloves I was wearing. What's funny is that I didn't even notice until I tried to take them off.
 
Veritech017 said:
This same safety rule is applicable to Bondo as well, you should always be trying to do this sort of stuff in the shade and not near anything flammable.
Aren't resin fumes flammable?
 
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Bigalt424 said:
Aren't resin fumes flammable?

That's what causes the fire. But it's better to have a pile of burning resin or bondo than an exploding car or gas tank. Or a cabinet full of spray paint.
 
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Veritech017 said:
That's what causes the fire. But it's better to have a pile of burning resin or bondo than an exploding car or gas tank. Or a cabinet full of spray paint.

Nope. Exothermic chemical reaction causes the fire. The fumes, while incredibly harmful, are not flammable per se.
 
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