As TotalBoat 2-Part Epoxy Primer cures, any air bubbles present in the coating, or under it, can pop, leaving little spots with no primer, which are sometimes referred to as pinholes. Common causes for this are air bubbles induced from foam roller covers, and moving the roller too quickly in a paint tray or on the surface when applying the product, or if there is a tiny cavity or pinhole in the substrate, such as a fairing material underneath. Always fill small pinholes in the substrate or fairing material before priming. If the primer is applied over a pinhole, the primer shrinks slightly as it cures, and does not have the tendency to fill or cover the gap.