Bubbles in Epoxy Resin — Causes and How to Fix Them
Air bubbles in cured epoxy ruin an otherwise perfect pour. The good news: most bubble problems are fixable during the open working time, and all of them are preventable. This guide covers every common source of bubbles and what to do about each one — before and after the pour.
Calculate exactly how much epoxy you need before your next pour — avoid over-mixing and the extra air it introduces.
Use the Epoxy Calculator →Quick Diagnosis
| What you observe | Most likely cause |
|---|---|
| Bubbles only on the surface, pop easily with heat | Mixing too fast / trapped air |
| Foam throughout the mix before pouring | Cold resin or high-speed mixing |
| Bubbles rising from the bottom after pouring | Outgassing substrate (wood, concrete) |
| Bubbles only near the edges | Substrate moisture at perimeter seam |
| Micro-bubbles (cloudy or hazy look) | Humidity or moisture contamination |
| Large bubbles that reform after torching | Porous surface not sealed |
Cause 1: Mixing Too Fast
What happened
Aggressive stirring whips air into the resin, creating micro-bubbles throughout the mix. Drill mixers at high speed are the most common culprit, but even hand-stirring with a circular motion can trap air.
The fix (during pour)
- Pass a propane torch or heat gun 6–8 inches above the surface in slow, sweeping motions
- Work within 10–30 minutes of pouring while the epoxy is still liquid
- Repeat passes every 5–10 minutes until the surface enters the gel stage
Prevention
- Stir slowly in a figure-8 or folding motion — never a circular whisk
- Keep drill mixer below 400 RPM
- After mixing, let the mix sit for 3–5 minutes to allow bubbles to rise before pouring
Cause 2: Cold Resin
What happened
Cold epoxy is thicker and holds air more stubbornly. If your resin is below 70°F (21°C), bubbles introduced during mixing are less likely to rise and pop before the epoxy begins to gel.
The fix
Warm both Part A and Part B bottles in a warm water bath (not hot — target 75–80°F) for 10–15 minutes before mixing. The thinner consistency allows bubbles to escape more readily both during mixing and after pouring.
Ideal working temperature: 72–80°F (22–27°C) for the resin, hardener, and room. Cold rooms slow curing and increase bubble retention simultaneously.
Cause 3: Outgassing Substrate
What happened
Wood, concrete, and other porous materials contain air in their pores. When epoxy is poured over an unsealed surface, heat from the exothermic reaction drives air out of those pores up through the epoxy — often after you've already passed the torch. Bubbles keep returning.
The fix
- Seal the substrate with a thin seal coat first (use the same epoxy, mixed correctly, brushed or rolled on thin)
- Allow the seal coat to gel fully (typically 4–6 hours)
- Then apply your flood or flood coat on top
The seal coat traps the substrate air before it can disrupt the flood coat.
Cause 4: Humidity and Moisture
What happened
Moisture on the substrate surface or in the air reacts with amine hardeners, releasing CO₂ micro-bubbles that create a hazy, cloudy appearance in the cured epoxy. This is distinct from air bubbles — moisture bubbles are smaller and distributed throughout rather than clustered at the surface.
The fix (before pouring)
- Work in relative humidity below 85%
- Wipe substrate with a clean, dry cloth immediately before pouring
- Allow the substrate to reach room temperature before applying epoxy (cold surfaces draw moisture condensation)
Moisture-caused bubbles cannot be removed after curing. The only fix is sanding and re-pouring under proper conditions.
Cause 5: Pouring Too Thick Too Fast
What happened
Deep pours generate significant heat (exothermic reaction). This internal heat drives bubbles up from the bottom of a thick pour faster than the surface tension can pop them. The result is bubbles throughout, not just on the surface.
The fix
Use a casting resin rated for your pour depth — most deep-pour resins are rated for 2–4 inches per layer. Tabletop/surface resins should not be poured more than 1/8–1/4 inch per layer. See: how thick can you pour epoxy.
Cause 6: Torch Technique Errors
What happened
Holding the torch too close scorches the epoxy surface (yellowing, cratering). Holding it too far or moving too slowly fails to pop bubbles. Torching after the epoxy has entered the gel phase moves surface material without popping bubbles.
Correct torch technique
- Use a propane torch or heat gun — not a lighter or hair dryer
- Hold 6–8 inches from the surface
- Move constantly in slow sweeping passes — never stop in one spot
- Work within 30 minutes of pouring (before gel stage begins)
- Pass 2–3 times at 5-minute intervals for best results
Frequently Asked Questions
How do I get bubbles out of epoxy after pouring?
Pass a propane torch or heat gun 6–8 inches above the surface in slow sweeping motions within 30 minutes of pouring. The heat thins the epoxy and lets bubbles pop. Work in multiple passes at 5–10 minute intervals while the epoxy is still liquid.
Why does epoxy foam when I mix it?
Mixing too fast whips air into the resin. Mix slowly by hand in a figure-8 or folding motion. If using a drill, stay below 400 RPM. Also warm the resin and hardener to 75–80°F before mixing — cold epoxy holds air much more stubbornly.
Can I use a hair dryer instead of a torch for bubbles?
A hair dryer is less effective than a torch — it moves air across the surface, which can push bubbles sideways rather than popping them. Use a propane torch or heat gun. If you must use a hair dryer, use low heat and hold it farther from the surface than you would a torch.