Bubbles in the epoxy resin may be from one of several sources – air or gas escaping from a substrate (when used for flooring for instance), humidity in the air, or choosing the wrong resin for the particular job at hand (they have varying thicknesses and properties). Working with the right resin (art, tabletop/floor, or marine), in the right environment (70–75 degrees, less than 75% humidity) and ensuring that all materials are at room temperature will help. When bubbles do occur, apply heat to the material before curing (very carefully) with a heat gun, butane torch, or barbecue lighter to pop them.
NOTE: When applying epoxy resin flooring over a porous slab, It’s best to seal the floor first with primer. This helps avoid pinholes in the finish. (And it may take two coats, but the process will be worth it!)