Why coatings unexpectedly fail

Rather than first looking at the reasons for bond failure, it may be more instructive to look at the reasons for a successful bond. The following are vital, minimum requirements for all successful coatings and adhesives, regardless of the type of material or application: Cleanliness of the substrate surface and elimination of weak boundary layers; wetting (intimate contact or spreading of the applied material onto the substrate surface); solidification of the coating or adhesive; formation of a 'joint'structure (applied material, interface region, and substrate) that is resistant to the operating stress and environment; and selection and control of all materials and manufacturing processes.