What causes chalking in epoxy coatings?

Chalking in epoxy coatings primarily results from exposure to UV radiation or sunlight. When epoxy coatings are subjected to UV light, the polymer chains undergo photodegradation, leading to the breakdown of the coating's surface. This degradation process creates fine powdery residues that can be easily wiped away, which is known as chalking.

Understanding the effect of UV radiation is crucial for coatings inspectors since it directly impacts the longevity and performance of epoxy coatings in outdoor environments. The degree of chalking can serve as an indicator of a coating's age and how effectively it has resisted environmental degradation. Coatings formulated for outdoor exposure often include UV stabilizers to help mitigate this issue, but even with these additives, some degree of chalking can occur over time.

The other options, while they can impact the performance of coatings, do not specifically cause chalking. Chemical reactions with solvents may lead to softening or blistering of coatings but not chalking. Improper surface preparation can affect adhesion and overall coating performance but is unrelated to the chalking phenomenon. Excessive humidity during application can also cause issues such as poor cure or bubbles but does not directly lead to chalking, which is fundamentally a UV-related degradation process.