Why Does My Resin Have Bubbles? (And How to Get Rid of Them)
You pour a perfect batch, set the mold aside, and come back two hours later. The surface is covered in tiny craters. Or worse — a whole galaxy of bubbles frozen just below the top layer.
It’s the most common resin problem I get asked about, and it’s almost always fixable. Usually preventable too, once you know what’s actually causing it.
Where Do Resin Bubbles Actually Come From?
There are two sources, and most beginners mix them up.
Mixing bubbles get trapped when you stir resin and hardener together. Air folds into the liquid every time you move your stir stick. The faster you stir, the more air you trap. These are usually uniform — tiny, dense, a little milky-looking.
Outgassing bubbles come from something inside the mold — a dried flower, paper, fabric, a wood coaster blank — releasing air as the resin warms up. These look different: bigger, irregular, rising from one specific spot like they’ve got a source.
Knowing which kind you’re staring at changes how you fix it. So before you reach for the torch, look at the bubbles for a second.
Warm your resin before you mix
This is the single biggest thing, and most tutorials skip past it.
Cold resin is thick, and thick resin traps air like a sponge. Before you open the bottles, set them in a bowl of warm water for about 10–15 minutes. You want the resin somewhere around 75–80°F (24–27°C) — not hot, just noticeably warmer than the room. It’ll flow easier and let air rise out on its own.
In Canadian winters this matters more than anyone admits. My studio is a converted spare room, and in January the resin sitting by the outside wall is a good 10 degrees colder than the resin on my desk. Same bottle, different shelf. I learned to just keep both bottles in the warm-water bowl every single pour from November to March, and my bubble problems basically halved.
Stir slow and deliberate
Slow circles. Scrape the sides and the bottom of the cup — that’s where hardener hides, and unmixed hardener means sticky patches sitting on top of your bubble problem.
I use a flat wooden craft stick and count out three minutes minimum for a 2:1 resin, two for a 1:1. Clock it, don’t eyeball it. And avoid whipping or folding motions — think “stirring a glass of chocolate milk without splashing.” That pace.
Pour from low, in a thin stream
Hold the cup an inch or two (2–5 cm) above the mold and pour slow. The more air the resin falls through, the more it picks up on the way down. That’s it — one sentence, but it’s a real one.
Heat is your best tool — but the torch has a learning curve
A butane torch or heat gun held 6–8 inches (15–20 cm) above the surface pops surface bubbles almost instantly. The heat drops the surface tension and they burst.
Here’s the part nobody warns you about: the torch is easy to overdo. My first one was a $15 micro-torch from Canadian Tire, and on my third or fourth piece I parked it maybe two seconds too long over one corner of a coaster. It came out with a scorched amber patch and a faint ripple in the surface, like the resin had flinched. Whole piece, garbage. So now I move constantly — two or three quick light passes over the whole thing, never lingering, never closer than about a hand’s width.
One other torch thing, since we’re here: keep it topped up with butane. A torch running low sputters and spits an uneven flame, and an uneven flame is exactly how you get that wavy, dimpled finish. I refill mine before a big batch now instead of halfway through — honestly just because I forgot once and ruined the back half of a pour.
If the torch makes you nervous, a heat gun on low (around 200°F / 93°C) is gentler and much harder to wreck a piece with. Good place to start.
And don’t run the heat once and walk off. New bubbles keep rising for the first 15–20 minutes, especially with inclusions in the piece. Stay close, do a pass, check again at the 10-minute mark, maybe once more at 30. After that the resin starts to thicken and whatever’s still trapped is staying trapped.
The sneaky kind: outgassing inclusions
If you’re embedding anything porous — dried flowers, wood, cork, paper, fabric — seal it first. A thin coat of Mod Podge, a brush of clear nail polish, or a quick pass of Krylon Crystal Clear seals the surface and stops air escaping into the resin. Let it dry all the way before you pour.
I had a batch of pressed botanicals once that looked bone-dry. Poured over them, walked away, came back to bubbles radiating out from every flower like little halos. Sealed the exact same flowers, repoured — perfectly clean. That one stuck with me.
Some woods outgas so hard that even sealed you’ll get micro-bubbles. For those: pour a thin seal coat of resin first, just enough to coat the wood, pop whatever rises in the first hour, let it fully cure, then pour your real layer on top.
Browse my handmade silicone molds for resin.
What if it’s already cured?
Then you’ve got two options, and both work — neither is instant.
Wet-sand the surface down with 220-grit until the bubbles are gone, wipe it clean, and pour a thin fresh top coat, usually 1/16 to 1/8 inch (1.5–3 mm). This is the move for flat pieces — coasters, trays, anything with a broad surface.
For a pendant or something small, skip the sanding and just dab fresh resin into each crater with a toothpick. Let it cure flat. Deep holes might need a second pass.
The one tool I’d buy first
If you take nothing else from this: get a small butane torch. It’s about $15–20 at Canadian Tire, Lee Valley, Home Depot, or Amazon, and it pays for itself on the first piece it saves. I resisted buying one for way too long — tried popping bubbles with a hair dryer, a straw, all the hacks. None of them really work. The torch does.
Have you had bubbles wreck a piece you were actually proud of? Tell me what you were pouring — sometimes it’s the material outgassing, not your technique, and that’s easier to narrow down than you’d think.
— Nikolai