In general epoxy based coating are formulated 100% solids meaning no solvent is incorporated in the system to dilute the resin systems viscosity and lower surface tension. Undiluted resins such 100% solid epoxy coating makes it harder for coating to effectively wet-out the surface and creates continuous film continuity.
A good example of poor wet out of a coating unto a substrate is the application of water into a waxed surface that equates to a discontinuous or beaded film layer of water. This poor substrate wet out is also good indicators of interlaminar adhesion of the coating to the substrate. It the surface tension of the coating cannot over come the surface tension of the substrate, the bond of the coating is superficial and can be usually peeled off in sheets.
When using an epoxy resin for thick coating applications, the exothermic heat generated by the resin system often causes coating surface blemishes.
POOR SURFACE WETTING
Due to the coating’s inability to overcome the LOW SURFACE ENERGY (LSE) or wettability of the substrate, the coating agglomerates and fails to create a continuous laminar film.
Benard cells are defects that look as if someone has imprinted a series of hexagonal shapes on the surface of the paint film.
The pattern can also may be four or five sided defined patterns that is either very subtle and can only be seen by angular view or very obvious patterns that can also be felt by light touch as well pronounce visual appearance.
Orange Peel, Pitting and Craters
Orange peel is noticeable bumpy visual defect on the surface of coatings. Is random and irregular surface pattern is very common to the texture of an orange peel hence the namesake. It is predominantly cause by poor substrate wetting and leveling of the coating. Other influences of this surface texture are the mirrored roughness of the substrate that is coated that is not well prepared for coating. Rather than being flat and smooth, the surface takes on the appearance of an orange peel, with numerous small bumps and craters.
Non-Top-Coat Functional Epoxy Resin Coating Formulation
Note the wavy pattern on the surface