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 in one of the experimental formulations. This is not Nerpa Casting Epoxy ;)
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:
The 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.
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.
- Start using vacuum degassing chamber
- Seal pores in the wood / warm the wood up
- 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
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