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small bubbles take longer to reach the epoxy resin surface

Small bubbles in epoxy. Why are they staying inside?

Small bubbles in epoxy. Why are they staying inside?

Microbubbles in cured epoxy

One of the common issues customers might experience with their projects is tiny microbubbles that are present in their epoxy after it is cured. This often happens with products that are not optimized for air release.

microbubbles often stay in epoxy layer in thicker formulationsMicrobubbles in one of the experimental formulations. This is not Nerpa Casting Epoxy ;)

Stokes' Law

These tiny bubbles don't rise to the surface because of the resin's high viscosity. Flow behavior is the single parameter epoxy manufacturer can control to facilitate bubble air release as the movement of bubbles to the surface is covered by the Stokes' law:

Stokes' Law application for epoxy resinThe speed of the bubble motion towards the epoxy resin surface is higher if the bubble's radius is higher and vice versa (bubbles with smaller radius move slower). At the same time, the higher the viscosity, the slower the motion of the bubble towards the surface. It becomes clear that the smaller the size of air bubbles trapped in your casting, the longer it would take for them to reach the surface, which is heavily dependent on the viscosity of the liquid.

Chemical reaction

It is important to remember that a chemical reaction begins when you mix the resin and the hardener together; individual molecules bond together to form a polymer network, inevitably raising the mixture's viscosity over time, thus making it harder for bubbles to move up.

Viscosity of the resin

According to the Stokes' Law, at a particular moment of the chemical reaction, the mixture's viscosity will become high enough to make the movement of the tiny bubbles infinitely slow even though larger bubbles can still escape from the resin.

If the viscosity of the resin you use is high right from the start, then the initial movement of the bubble of all sizes will be slower and stop sooner than if you use low viscosity resin optimized for air release.

How to avoid microbubbles in the epoxy casting or deep pour?
  • Use high quality, low viscosity resin.
A simple and easy solution can help improve your resin projects' quality. Low viscosity casting epoxy resin features properties and flow to overcome the slowing down movement and stall of microbubbles in thicker resins. Nerpa Polymers Casting Epoxy has one of the lowest viscosities on the market (Nerpa's Casting Epoxy 215-250 Centipoise while the industry standard for deep pour resins is 400-600 Centipoise. The higher the Centipoise number, the thicker the resin).
Nerpa Casting Epoxy is a low viscosity system optimized for air release
  • Start using vacuum degassing chamber
Another good way to improve the visual clarity of the casting is to use degassing chamber prior to pour. Negative pressure in the chamber will force bubbles to rise to the surface faster and and pop. On the other hand, vacuum degassing chambers are usually too small to accommodate large quantities of resin and using them might require extra time and effort.
  • Seal pores in the wood / warm the wood up
If you are going to use wood with epoxy, it would be a good idea to seal it or to warm it up before pouring the epoxy. These two effective tricks will help stop the formation of the small bubbles from the pores and wood cracks. You can read more about these techniques in our "How to remove air bubbles from your epoxy" blog post.
    What you should definitely avoid doing: 
    • Increasing temperature in your shop

    Although higher temperature lowers the viscosity of the epoxy resin, we do not recommend working in the warmer conditions or preheating your epoxy resin for deep pour projects as it might enter the exothermic runaway (warm up quickly to high temperatures). 

    • Thinning your epoxy with solvents or alcohols
        Diluting or thinning resin with solvents and/or alcohols is detrimental to the structural properties of epoxy, especially in deep pour applications.
        We encourage to share your tricks and thoughts in the comment session!


        • I can attest, this stuff is the best for bubble free casting. I’ve been frustrated with other epoxies trying to get a bubble free cast, with this epoxy it’s just night and day. No bubbles awesome..

          Richard Bell on

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