Air inclusion can occur when mixing two part epoxy liquid systems by hand. It is recommended that mixing be done slowly to prevent injecting air into the compound. Faulty mixing can cause voids, resulting in poor adhesive performance. Often air release agents are employed in the formulation to remove bubbles and maximize bond line effectiveness. When over-agitation does happen, reducing viscosity by heat, vacuum degassing or centrifuging may be necessary.
A convenient, simple method to remove air from epoxy is to heat the system between 35°C to 40°C in a shallow mixing vessel. This should be done for a short time period, depending on the volume of bubbles.
Another widely used technique is vacuum degassing. The mixed epoxy should be place in a vacuum chamber. The size of the container should be 5 to 10 times the volume of the epoxy. A vacuum of 29 inches of Hg needs to be pulled. To achieve the best results, a bumping technique is recommended, which involves a few cycles of pulling and releasing the vacuum.
High quality deaeration can also be accomplished with a centrifuge at 1,000 to 3,000 rpm for a few minutes.