Which of the following is NOT a factor affecting coating adhesion?

• A. Coating color
• B. Surface cleanliness
• C. Rust scale
• D. Moisture

Answer: (A)

Adhesion of a coating depends on how well the surface is prepared and free of contaminants so the coating can wet the surface and bond to it. Surface cleanliness is crucial because oils, dirt, or residues create a barrier that prevents proper wetting and bonding. Rust scale, being an oxide that can be flaky and uneven, disrupts a uniform interface and weakens adhesion. Moisture at the interface can reduce surface energy and interfere with curing or bonding, leading to poor adhesion or delamination. Coating color, on the other hand, is cosmetic and does not change the surface chemistry, roughness, or moisture conditions that control adhesion, so it does not affect how well the coating sticks.