Epoxy Woes

I'm working on a desk for my wife that uses a big live edge walnut slab for the top. There's a big honking knothole that needs to be filled. No big deal. I've done epoxy fills before. It's always worked well, until now.

I'm using Alumilite Clear Cast (link) with a drop of black dye. I've used it in the past with good success.

The first try I mixed it up and added a couple drops of india ink. I poured, popped any air bubbles, and looked forward to picking the project up when it hardened in a day or two. Two weeks later it was still soft, about the same durometer as the rubber on a tire. I chalked it up to the solvent in the ink.

I dug it all out and mixed another batch. Ratio was watched very carefully and I mixed thoroughly. I added a drop of Transtint Black, as the Alumilite instructions indicated compatibility with alcohol based inks and dyes. A week later it's very soft and sticky like tar.

My shop is in the basement, and temperature is in the mid to high 60's. I warmed the fill up with a hair dryer as Alumilite suggests cooler temps will retard the hardening process. We'll see what it looks like tomorrow.

I've had the epoxy material for at least a couple years. Could I be bumping up against a shelf life issue? Any other words of wisdom from those that do this regularly?

The only times that I have had that kind of problem with epoxy is either very old epoxy, too much liquid tint, or wrong mixing ratio. I usually use powdered colors to tint epoxy.

The marine epoxies I have used have a virtually unlimited shelf life. The hardener may get dark and stinky over time but it still does the job and if the resin thickens up it can be decrystallized in a warm water bath. I would check with the alumilite manufacturer about their shelf life and minimum curing temp. Assuming the correct mixing ratio it should work. It's hard to imagine a drop of transtint would prevent curing.

Does big honking mean deep too? A deep pour resin would have been a better choice. Either move the slab out in direct sunlight, or put a heat lamp over it. I only use Alumilite dye or used coffee grounds.

My one thought is to mix some of the epoxy up per proper ratios with no tint or other additives. See if it sets up properly - if not, you know your epoxy has gone off in some way (not sure what would cause this). If it does set up properly, think you know your tints/additives are the problem.

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Originally Posted by Richard Coers

Does big honking mean deep too? A deep pour resin would have been a better choice. Either move the slab out in direct sunlight, or put a heat lamp over it. I only use Alumilite dye or used coffee grounds.

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I did the pour in stages. The first stage is hardened as expected, but it's been there for 6 weeks. The depth of the second pour is about 1/4" and well within the claimed limits of the epoxy. I'll look for the Alumilite dye. The guy at my local woodworking outlet claimed repeated success with the TransTint stuff but he might be using a different epoxy product.

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Originally Posted by Mark Wedel

My one thought is to mix some of the epoxy up per proper ratios with no tint or other additives. See if it sets up properly - if not, you know your epoxy has gone off in some way (not sure what would cause this). If it does set up properly, think you know your tints/additives are the problem.

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An experiment is in process. I also mixed a larger batch. The instructions mentioned that the product was less forgiving with small batches of a fluid ounce or less. I mixed up a 3 oz batch and stirred the bejesus out of it before pouring it in a mold (yogurt container lid). The A to B ratio was as accurate as possible. I did dye it, as the manufacturer's instructions claimed compatibility with alcohol based dyes. I'll know tonight if it was a mixing or measurement error on my part.

I'm hoping I can crack the code here. I don't want to have to dig the epoxy out again and my wife would really like to have her desk completed.

Well, it sounds like it's setting, sot hat is good.

I had this issue with some epoxy in a cold basement. I put an incandescent lamp over it and it set up quickly, a bit too fast in fact. I measured the surface temp of the board at 130. This led to some cracking.

Try getting it a bit of heat. Could be an incandescent heat lamp, maybe a laptop fan. Nothing too aggressive.

Wonder if a heating pad would be a reasonable way to heat it also. I often use one to warm my bread dough so that it rises faster.

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Originally Posted by Mark Wedel

Wonder if a heating pad would be a reasonable way to heat it also. I often use one to warm my bread dough so that it rises faster.

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I've used electric blankets for veneering/lamination in the past.

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Originally Posted by Rob Luter

I did the pour in stages. The first stage is hardened as expected, but it's been there for 6 weeks. The depth of the second pour is about 1/4" and well within the claimed limits of the epoxy. I'll look for the Alumilite dye. The guy at my local woodworking outlet claimed repeated success with the TransTint stuff but he might be using a different epoxy product.



An experiment is in process. I also mixed a larger batch. The instructions mentioned that the product was less forgiving with small batches of a fluid ounce or less. I mixed up a 3 oz batch and stirred the bejesus out of it before pouring it in a mold (yogurt container lid). The A to B ratio was as accurate as possible. I did dye it, as the manufacturer's instructions claimed compatibility with alcohol based dyes. I'll know tonight if it was a mixing or measurement error on my part.

I'm hoping I can crack the code here. I don't want to have to dig the epoxy out again and my wife would really like to have her desk completed.

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Experiment complete. It’s hard as stone after 24 hours. I guess I just need to mix up 2 or 3 times the volume I need and stir it for a good long time.