3. Adhesion

Most coatings are applied for a specific purpose: decoration, corrosion protection, etc. It is therefore essential that the coating adheres well to the substrate in order to achieve this purpose. Adhesion is a measure of both the quality of the preparation of the surfaces to be coated and the quality of the coating operation.

Perfect adhesion exists when the bonding force between the coating and the substrate is greater than the inherent strength (e.g., tensile strength) of each. The purpose of the adhesion test is therefore to identify cases of imperfect adhesion.