Bubbles in Epoxy: Cause, Fix, and Prevention

Short answer: Most bubbles come from mixing too fast, air trapped in porous wood, or a pour that is too thick for the product. Seal porous wood first, mix slowly and thoroughly, pour in the recommended layers, and remove surface bubbles while the epoxy is still wet.

Close-up of air bubbles trapped inside cured epoxy between wood slabs

What causes them?

Mixing air in. Fast, vigorous stirring whips air into the resin. That air has to go somewhere.
Wood outgassing. Air in porous wood rises into a fresh coat, especially on an unsealed surface.
Wrong product or layer. A thin coating product poured thick, or a deep pour poured past its recommended layer, traps more air and heat.
Dust and debris. Dust on the surface can hold air and show up as small bumps that look like bubbles.

Fix: while it is still wet

Heat gun held above an epoxy river-table surface for bubble removal

Work promptly, while the surface is still liquid.
Use a heat gun briefly, held at a distance and kept moving, to help surface bubbles rise and pop. Do not hold heat in one spot, and do not overheat the epoxy. Keep heat away from acetone, denatured alcohol, and their vapors, and let any solvent wipe dry completely first. Both are flammable.
Check again after a few minutes. New bubbles can rise from the wood after the first pass.
Do not keep stirring a poured coat. Stirring after pouring adds air back in.

Fix: after it has hardened

Sand the affected area smooth, so the bubbles are opened and level.
Remove all dust, and clean with a lint-free rag.
For a Bar & Table Top Epoxy repair more than 10 hours after the previous coat, lightly scuff with 220 to 320 grit, clean with a lint-free rag and denatured alcohol or acetone, let the cleaner evaporate fully, then recoat at 1/8 inch. For a Deep Pour casting, follow its approved repair instructions and the 12 to 24 hour inter-layer window. Do not apply Deep Pour thinner than 1/4 inch.
If bubbles run deep through a cast, sanding and a thin recoat will not fill them. That area may need to be sanded back further, or, in a severe case, reworked. Do not just pour a thick coat over a badly bubbled surface and hope it hides.

Prevent them next time

Mix slowly and thoroughly, scraping the sides and bottom, without whipping air in.
Seal porous wood first. For a bar top, use a thin seal coat before the flood coat.
Pour in the recommended layers: 1/8 inch flood coats for Bar & Table Top Epoxy, and 1 inch layers as the standard for Deep Pour Epoxy.
Work on a clean, dust-free surface, and keep dust off the piece while it sets.
Follow the product instructions for temperature and working conditions. A cold, damp, or dusty room makes bubbles more likely, not less.

Questions about bubbles in epoxy

Why do bubbles keep coming back after I use a heat gun?

If bubbles disappear and quickly return, air is often escaping from wood that was not fully sealed. Rough or very porous wood can need two or three Bar & Table Top Epoxy seal coats before the flood coat. More heating does not replace sealing. Follow the product’s recoat timing when applying additional seal coats.

Do I need a vacuum chamber to prevent epoxy bubbles?

No. A vacuum chamber is not required for normal UltraClear Bar & Table Top or Deep Pour projects. Seal porous materials, measure and mix as directed, use the correct pour depth, and remove surface bubbles with brief, moving heat while the epoxy is liquid. Follow the instructions for the specific product you are using.

Can a drill mixer cause tiny bubbles in tabletop epoxy?

Yes. A drill mixer can whip excess air into a small batch. For UltraClear Bar & Table Top Epoxy, mix batches under one gallon combined by hand with a stir stick. A drill mixer is for a full one-gallon batch, used as directed with the paddle below the surface. Avoid a vortex and vigorous mixing.

Does cold resin make air bubbles harder to remove?

Yes. Cold resin is thicker, which makes it harder to mix and lets it hold onto air bubbles. Bring the bottles and workspace to the temperature specified for your product before measuring and mixing. Bar & Table Top and Deep Pour have different temperature requirements, so follow the correct instructions rather than using one heating routine for every resin.

Can I heat bubbles out after the epoxy has hardened?

No. A heat gun removes surface bubbles while epoxy is still liquid; it will not release air trapped in a hardened coating. Let the epoxy reach the repair stage specified in its instructions, sand out the affected material, then clean and recoat as directed. Bubbles deep inside a casting may require more extensive removal and repair.

Can I repair one bubbled spot without recoating the whole tabletop?

A small Bar & Table Top Epoxy spot repair is possible after the bubbles are sanded out and the area is properly cleaned, but it can leave a visible edge or uneven sheen. For a consistent finish across the top, scuff and clean the whole surface, then pour a new flood coat. Seal any bare wood exposed during sanding first.

How do I prevent bubbles around wood, corks, or embedded objects?

Start with clean, completely dry objects. Seal porous wood, corks, and similar materials with Bar & Table Top Epoxy before embedding them, so trapped air does not escape into the casting. Choose the resin for the required layer depth, and test an unfamiliar object in a small sample before committing to the finished project.

How can I reduce bubbles in a Deep Pour river table?

Seal the wood first. Pour Deep Pour in approximately ¼-inch passes, clearing surface bubbles between passes as you build the planned layer. These passes happen in the same pouring session; they are not separate overnight layers. Use one-inch layers as the standard, and follow the 12-to-24-hour window before the next casting layer. Avoid mixing extra air into the resin.