How to avoid bubbles in epoxy (and get rid of them)

Where bubbles come from

1. Mix without whipping air in

Stir slowly and deliberately, keeping the stick in contact with the sides and bottom rather than lifting it in and out. Don’t use a fast drill; a paddle mixer is useful for big batches but should run at low speed with the paddle kept below the surface. Mixing for the full time on the label is still important — slow doesn’t mean short. Letting the mixed batch sit for a minute or two (within the working time) lets many large bubbles rise before you pour.

2. Seal porous surfaces first

Wood, concrete, cork, paper and fabric all contain air. As epoxy flows into the pores it pushes that air out, and it rises through your pour as bubbles — sometimes for hours. The fix is a thin seal coat: brush or scrape a thin layer of epoxy over the surface, work it in, and let it cure to the recoat window before the main pour. On live-edge slabs, pay extra attention to bark, knots, cracks and end grain, which release the most air. The seal coat for a 6 ft slab example shows how much epoxy this step takes.

3. Work at the right temperature

Cold epoxy is thick, and thick epoxy holds bubbles. Keeping the resin, hardener and workspace within the label’s range — often somewhere around room temperature — lets bubbles rise and escape. Some people warm the unopened bottles in a bath of warm (not hot) water before mixing to lower the viscosity.

4. Pour the right thickness

Deep pours trap air simply because it has further to rise, and a pour that overheats can generate bubbles of its own. Respect the maximum depth per pour on the label and use lifts (separate layers poured one after another) for anything deeper — a 7 ft river table with thick slabs is the typical case. For tabletop epoxy, around 1/8 in per coat is the usual target; a coating poured much thicker than it’s designed for tends to trap bubbles and may overheat.

5. Pop surface bubbles with heat

After pouring, bubbles that reach the surface can be popped with a quick pass of heat. A heat gun or a small torch both work: warming the surface lowers its viscosity and surface tension for a moment and the bubbles burst. Keep it moving, a few inches above the surface, and make several light passes over the first part of the working time rather than one long one.

• Torch: fast and effective on flat coatings. Don’t linger — it can scorch, ripple or yellow the surface. Keep it away from tape, paper and solvent vapors.
• Heat gun: gentler and safer around flammables, but it blows air — use a low fan setting to avoid pushing the resin around or blowing dust in.
• No heat source: a light mist of isopropyl alcohol is sometimes suggested for small art pieces; test it first, as it can affect some finishes.

6. Molds and embedded objects

Bubbles love the fine details of silicone molds and the undersides of anything you embed. Brush a thin layer of resin into detailed mold areas first, then pour the rest slowly from one corner and let it flow across. Pre-coat flowers, bottle caps and other objects with a thin layer and let it set before embedding, so they don’t release air into the main pour. Pressure pots are used for bubble-free castings but are a bigger investment and have their own safety requirements. Two projects where this matters most: a bottle cap bar top, where every cap traps a pocket of air underneath, and small resin pendants, where one bubble in a thin piece is very visible.

Fixing bubbles after it cures

Small surface bubbles in a cured coating can usually be sanded out and covered with another coat. Sand the whole surface evenly (not just around the bubble), clean off the dust, and pour a fresh flood coat — it will fill the sanded pits. Bubbles trapped deep in a river pour are harder: you can drill or rout them out and fill with fresh epoxy, or accept them as part of the look.

A quick bubble checklist

1. Seal-coat wood and other porous surfaces; let it cure.
2. Bring resin, hardener and room into the label’s temperature range.
3. Measure exactly and mix slowly for the full time.
4. Pour at or below the recommended thickness.
5. Pass a heat gun or torch lightly over the surface several times in the first part of the working time.
6. Cover the piece against dust once the bubbles are out.