Hand up if you hate bubbles in resin! (I have both of mine up in case you are wondering.) Nothing can ruin the look of resin quicker than finding a bubble in your finished project. Here are my 10 tips for avoiding and getting rid of resin bubbles.
1. Choose the right resin for your project.
If you are casting into molds, choose a resin that is designed for casting. They mix in a thinner viscosity, so it is less likely you will introduce bubbles into the resin. Even if you do, they also tend to release easier since the resin and hardener mixture is thinner. Thicker resins, meant for doming projects, generally hold bubbles, especially with thick castings. Doming resins are better suited for thinner pours.
👉 Troubleshooting Tip: If you accidentally use a thicker doming resin for casting, try warming it slightly before mixing. This can help it flow better and release bubbles. However, be careful not to overheat, as it could cure too quickly.
2. Cast resin in a warm room.
I realize that certain times of the year it can be difficult and expensive to run a heater all the time, but resin likes an ambient room temperature of 20 to 24 degrees Celsius for curing. If it is a little impractical to heat your whole house or apartment, try heating a smaller space such as a bathroom or closet. Use something like a space heater to generate enough warmth so that the area stays warm during the entire curing time. You can also try making a resin ‘hot box’ for your projects. This works great for smaller undertakings like casting resin into molds and bezels.
👉 Troubleshooting Tip: If you’re working in a cold environment and your resin has already started to cure with trapped bubbles, you may be able to warm it gently with a heat gun while it’s still in the soft stage. This might allow some bubbles to rise before it fully hardens.
3. Warm your resin before casting.
Warm water in your microwave so it’s hot, but not boiling. Place your resin and hardener bottles in a plastic bag, then let the bag sit inside the hot water bath for five to ten minutes. Be aware, you do not want to get water in your resin. This could keep it from curing! Note: By keeping the resin in the plastic bag, you will not wash off your label instructions and safety information. Warming your resin before use is helpful even if it is summertime as bottles generally are still cool to the touch. Be careful that you don’t overdo it. Yes, there is too much a good thing. If your resin is too warm when mix it, you will shorten your pot time.
👉 Troubleshooting Tip: If resin becomes too thin, it might not hold inclusions well, causing them to sink. This is especially important for lightweight elements like dried flowers, glitter, or small embellishments.
4. Be careful when mixing.
You are not scrambling an egg! Mix deliberately, but carefully, while going along the sides and bottom of the cup. Sometimes when mixing large volumes of resin, it’s hard not to introduce bubbles that may not rise to the resin surface before casting or pouring. Know that you will need to have a way to get rid of these bubbles once you have cast the resin.
👉 Troubleshooting Tip: Use a flat-edged stir stick (rather than a round one) to reduce bubbles further. A flat-edged stick helps break up trapped air pockets and ensures even mixing.
5. Make sure the surface you are pouring your resin in or on is also warm.
Temperature differences will produce surface tension which means bubbles can be trapped when the resin is poured. Gently warming your casting top/mold/bezel with a heat gun is an easy way to warm up the area. If you are working with molds that are oven-safe, you can also gently warm them (generally to 65 celsius) before use.
👉 Troubleshooting Tip: If your resin is already curing and bubbles are stuck near the surface, try using a toothpick or needle to break them before they harden completely.
6. Decrease the surface tension of a mold by dusting a powder on the surface.
A small amount of baby powder can work to reduce bubbles in resin. If you are using colored resin, you can even choose a powder that matches the color of the resin you are using. Use a delicate paintbrush to dust in the powder, then tap out any extra before pouring.
👉 Troubleshooting Tip: If too much powder is applied and the resin doesn’t stick properly, try lightly buffing the surface with a soft cloth once cured to remove any residue.
7. Roll the resin around your mold/bezel before completely filling the vessel.
This also helps to break the surface tension. If you do get any bubbles, they will be easier to pop now because there is less vertical space for them to move. You have them trapped!
👉 Troubleshooting Tip: If you forget to do this step and see bubbles forming, use a toothpick to push them toward the surface before they cure.
8. For intricate molds, pick them up and try to ‘demold’ the resin several times during pouring.
This will let any trapped bubbles in creases to escape.
👉 Troubleshooting Tip: If bubbles get stuck in small details, use a soft-bristled paintbrush to spread resin into tricky areas before pouring the full amount.
9. Dip inclusions in resin before putting them into your mold/bezel. This also breaks the surface tension.
Once you have dipped them into the resin, put them into your mold or bezel on an angle, then move into place. By putting an inclusion flat onto a resin surface, you will likely trap bubbles underneath.
👉 Troubleshooting Tip: If you notice bubbles forming around an inclusion after pouring, use a heat gun or a fine needle/toothpick to release them before the resin fully cures.
10. Once you have cast all your resin, go over it a final time with a heat source to pop bubbles.
I like to use a heat gun, but I know others will also use a butane torch or barbecue lighter. Please use caution when using a flame! You should have a fire extinguisher nearby. Also, know that excess heat may warp plastic molds.
👉 Warning: Overheating resin can cause yellowing, scorching, or even warping of molds. Always keep your heat source moving and avoid holding it in one spot for too long.
👉 Troubleshooting Tip: If you accidentally overheat resin and it develops a slightly burnt surface, try sanding it down with fine-grit sandpaper (400-600 grit) and applying a thin new coat of resin to restore clarity.
Bonus tip: If all else fails and find you are still struggling with removing bubbles from your castings
11. Use a pressure pot.
With some resins (like clear polyurethanes) and/or large castings, the only way you can get rid of bubbles is to use a pressure pot. This is a system where your mold and casting are placed into a pot and pressure is created within the pot. This pressure makes the bubbles smaller than the eye can see. The pressure needs to remain on the casting the entire time during which the resin will cure bubble-free.
Troubleshooting: How to Fix Bubbles in Cured Resin
Missed a step? Don’t worry—if you find bubbles in your cured resin, you may still be able to fix it!
🔹 Small surface bubbles:
Use a fine grit sandpaper (400-600 grit) to gently sand the area.
Apply a fresh thin coat of resin to smooth the surface.
🔹 Deep bubbles inside the resin:
Drill into the bubble using a small handheld drill.
Fill the hole with fresh resin using a toothpick or needle.
Allow to fully cure and sand if needed.
🔹 If all else fails…
Embrace imperfections! Some bubbles can add character to homemade resin pieces. Consider incorporating them into your design rather than stressing about perfection.
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