What does checking in a coating refer to?

Checking in a coating refers specifically to the formation of fine cracks on the surface of the coating. These cracks are generally superficial and do not extend through to the substrate, which means that the integrity of the underlying material is maintained. Checking is often a sign of stress in the coating, which may be caused by factors such as age, environmental conditions, or improper application techniques.

Understanding this concept is crucial for coatings inspectors, as recognizing these types of defects can help in assessing the overall health of a coating system. The other options represent different types of coating failures or defects that occur under more severe conditions, such as large cracks or flaking, but checking itself is characterized by the presence of those fine cracks that do not compromise the substrate.