Why Your Epoxy Pour Keeps Going Wrong

If you've ever tried a thick epoxy cast and watched it go sideways - smoking, bubbling, completely ruined, you already know the feeling. The frustrating part? It's almost never bad luck. It's one specific mistake in the preparation, and once you see it, you can't unsee it.

This week we're diving into exactly that: how to prep your epoxy cast properly, which sanding paper actually matters after the cure, and a quick trick to keep exothermic reactions from ruining your next pour.

Article summary:
Most epoxy mistakes don't happen during the pour, they happen before it. Wrong epoxy for the depth, a mold that's not quite flat, not enough resin ordered. Small decisions that feel insignificant until the cast is already in the mold.

Key takeaways:

👉 Continue reading:
Epoxy Casting for Beginners: Complete Preparation Guide (2026 Edition)

This one's from a while back, but it still gets the most questions: a beech wood multicolor 3D epoxy serving tray. The kind of piece where people pick it up and ask "how did you even make that?"

The layout is simple: beech on one side, deep-pour epoxy on the other, joined edge to edge. The dark epoxy strips running along the long sides double as handles - clean, no extra wood. But that epoxy panel is where the real work lives. The greens, dark browns, and transparent portions aren't just poured - they're layered in sequence, each color timed to hit the previous one at exactly the right gel stage. Too early and they bleed into each other. Too late and you get flat, hard boundaries with no depth. That narrow timing window is what gives it the swirling, almost organic look.

That's what makes this project a real test. It's not about technique alone - it's about reading the resin as it cures, and adjusting on the fly.

For designers:
the 3D color effect catches light differently depending on the angle - which means this tray actually changes how it looks depending on where you place it. A kitchen counter with overhead light will read completely differently than a side table with natural window light. Lean into that. And the Osmo TopOil finish keeps it practical too, it's certified for food contact, resistant to spills, and won't crack or peel. Functional and good-looking without the guilt of wondering if it's safe to use.

When I first started sanding epoxy, I grabbed regular wood sanding discs I had in the workshop. Lasted less than a minute before they were completely clogged - useless. High gloss finish? Not even close. So I started digging into what professionals actually use, and that's how I ended up with this setup. I've tried a few things since, but nothing has beaten it yet.

I run a two-product setup, both from Kovax. For the rough stuff, straight off the mold, removing the bulk, I use Tri-Pro discs. They're resin-bonded, cut fast, and have an anti-clogging coating that matters a lot when you're grinding down thick epoxy. I run those from 100 through 400. No point in spending more here, the surface is still too rough for anything precious.

At 600 I switch to Super Assilex. That's where precision starts to matter. The latex backing and uniform grain structure give you a consistent, shallow scratch pattern, no surprise gouges, no uneven wear. I step through K600 → K800 → K1200 → K1500, then finish with Kovax Buflex Dry from K2000 to K3000 for the final polish. Super Assilex stops at K1500, pushing it further just wastes discs.

⚠️ One thing to watch: Super Assilex needs an interface pad between the disc and your sander. Hard pad for K600, soft pad from K800 up. Skip the interface and the velcro hooks will scratch right through your surface.

Bottom line: Tri-Pro for the heavy lifting, Super Assilex for the finish. Two products, each doing what it's built for. I wouldn't use generic sandpaper for either stage on epoxy.

If your epoxy instructions say "max 5 cm per pour", believe them. But pour thickness isn't the only thing that triggers it. Maximum mixing volume matters just as much. Mix too large a batch at once and the heat builds up in the cup before you even get to pour. Both specs are on the packaging, respect both of them. Exothermic reactions build heat from the inside out, and once it starts, there's no stopping it. The real fix? Buy the right epoxy for your project in the first place. A proper deep-pour resin is formulated to handle the heat. Cheap or wrong-spec epoxy is where most exothermic boiling comes from. If you're still working with what you have, pour in smaller batches: 2 cm at a time, letting each layer reach a tacky gel (not fully cured) before adding the next. Slower, yes. But your project survives.

everything in this issue ties back to one idea: the steps you take before you pour matter just as much as the pour itself. Prep is unglamorous, but it's the difference between a piece you're proud of and one you're scraping off the workbench.

I'm curious what's tripping you up right now, so I can make sure we cover it:

Next week: once the cast is cured, the real work begins. Processing, cutting, sanding - done right. Don't miss it.

Petr from Resin Craft Guild
www.resincraftguild.com