Adhesion

The bond between a coating and a surface, or a bond between two coatings. The means of adhesion is primarily mechanical, which requires that the coating comes into intimate contact with the substrate. (Substrate = a more fancy term meaning surface). If the surface is dirty, waxy, oily or slick, the coating will be prevented from contacting substrate and poor adhesion will result.. To gain excellent adhesion it may be necessary to clean, degloss, or roughen the surface.

A Tape AdhesionTest is the most common method used to evaluate the adhesion of a coating to a surface. In simplified terms the test requires cutting an X-pattern or # crosshatch pattern through the coating down to the substrate with a razor blade. A strip of tape is firmly applied over the cuts and then removed. The adhesion is rated based on the amount of coating removed with the tape. See ASTM D3359 for the precise explanation.

Cohesion

A coating forms a film that may be 0.5 mil to 3.0 mils thick when dry. Cohesion refers to the integrity inside that film. The molecules in the coating film must be bonded inside the film sufficiently to prevent the damage from light surface.

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