I poured an epoxy river cast and it took off on me even when in a cool environment and with fans.
I'm looking at fixes for this without chipping everything away.
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Ouch! When epoxy fails it fails, but usually not quite so spectacularly as this. As I'm sure you'll have picked up from elsewhere, there's no repairing this. Even with opaque fills patching can be dubious (the margins tend to remain noticeable and bonding is questionable) but with a clear fill even the tiniest defect is plainly visible. through the full thickness.– GraphusJul 20, 2021 at 14:54
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1"and with fans" Possibly worth pointing out that fans don't cool air? They make us feel cooler because of evaporation, but air itself is a poor conductor (it doesn't carry heat away efficiently) and there's zero evaporative cooling with epoxy since there's no water in it.– GraphusJul 20, 2021 at 14:57
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1@Graphus you may as well turn that first comment into an answer. This epoxy look is common enough no doubt it'll be useful for others.– user5572Jul 20, 2021 at 17:07
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As I'm sure you'll have picked up from elsewhere, you can't repair this. I will bet you'll find at least someone who's tried to recover from something similar to this by pouring in more epoxy but clearly (pardon the pun) the best idea here is starting again. Even assuming you patched the cracks and somehow they turned out well enough to be acceptable you have obvious fracture planes in a few places at the wood/epoxy juncture, and there's no coming back from those. In addition to how visible those fractures are, they may actually indicate that there's no bond to the wood at all.
Next time
Just in case it is an idea that you considered, it's not viable to refrigerate one or both of the components before mixing. Cold-weather recommendations for epoxies almost always call for the liquids to be pre-warmed before mixing, both to help with accurate measurement and also to ensure proper curing.
If you want to continue to use what you have it's worth investigating if there's a slower hardener available as that's one of the classic ways to control temperature rise in resin mixtures.
Numerous other tips to be found at the following links:
Controlling Exotherm
Temperature: The Ultimate Variable
Why is my epoxy resin hot and smoking?
in a cool environment and with fans
It's possibly worth pointing out that fans don't cool air.
They make us feel cooler because of evaporation (that's what sweat is for), but air itself is a poor conductor — it doesn't carry heat away efficiently — and there's zero evaporative cooling with epoxy since there's no water in it.
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1To nitpick, airflow does cool things. Otherwise cars would overheat (both air-cooled and water-cooled cars dump the heat into the air) and air conditioners wouldn't work. You are correct that airflow is more effective when facilitating evaporative cooling, but it will still help cool a warmer-than-ambient object. As epoxy cures exothermically, running a fan should help cool it down to ambient temperature, but not lower (as opposed to evaporative cooling that can get lower than ambient).– Eli IserJul 23, 2021 at 13:17
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Yes of course airflow does cool things, but not efficiently (unless the surface area is large, hence the design of rads and finned bodies of air-cooled engines). Pretty hard to increase the surface area of an epoxy pour ^_^ Seriously though, it is worth noting that high-level epoxy guidelines that address mitigating post-mix heating will always mention having the workplace cool in advance, but typically don't mention the use of fans at all. My bet is that unless the air is already cooled running a fan does squat — increased flow of RT air over a pour won't produce any noticeable cooling.– GraphusJul 24, 2021 at 17:54