Bubbles are the most common complaint in resin art. A cast that should look like glass comes out of the mold cloudy with tiny specks. Most of the time the resin is not faulty. The bubbles come from how it was mixed, poured and cured, and every one of those is something you control.
Steve McDonald of Steve McDonald Arts and Crafts proves it with two sphere molds of the same size. One gets a deep pour resin, the other a fast 1:1 resin. Same pour, same tapping, same flame. The fast resin cures in about two hours full of trapped bubbles. The deep pour takes 48 hours and comes out almost clear.
Where epoxy resin bubbles come from
- Mixing. Whipping the resin folds air in.
- Pouring. A fast, thick pour traps air against the mold walls.
- Cold resin. Cold resin is thick, and bubbles cannot rise through it.
- Fast cure. Resin that sets in an hour locks bubbles in place before they reach the top.
Why the resin type matters most for deep casts
Epoxy gives off heat as it cures. In a thick casting, a fast resin heats up quickly, thickens and sets before bubbles can escape. It can also warp or ripple. A deep pour resin reacts slowly. It stays thin for hours, so bubbles have time to float up and pop on their own, even without a pressure pot. Use a 1:1 coating resin for thin layers like coasters and tray tops, and a deep pour resin for anything thicker than about an inch. If you are new to mixing, read how to mix epoxy resin first.
Other ways to get bubbles out of resin
Warm the bottles. Stand the closed bottles in a bowl of warm tap water for 10 minutes before you measure. Thinner resin lets bubbles out faster.
Heat gun. Works on flat pours. On small molds it can blow the resin around, so keep it on low.
Pressure pot. Squeezes bubbles too small to see. Worth it if you cast a lot, but not needed for most home projects.
Toothpick. Lift a stubborn bubble out of a corner or a detail in the mold.
Mix colour in gently. Pigment and glitter carry air in with them. Stir them in slowly after the resin is mixed.
Torch or lighter on silicone molds?
Steve uses a long-neck lighter, never a torch, on silicone molds. A torch flame is hot enough to scorch the silicone over time, and a damaged mold leaves marks on every cast after it. Keep the flame moving and a few inches above the surface. Two or three quick passes are enough.
Troubleshooting
Bubbles stuck to the sides. The resin set before they could rise. Use a slower resin or pour in thinner layers.
Cloudy all the way through. Usually a cold room or over-mixing. Work above 70 F and mix slowly.
Soft or tacky after curing. The ratio was off. See how to fix sticky resin.
Ready to cast? How to use resin molds and how to make resin coasters are good first projects to practise a bubble-free pour.
