What is the characteristic feature of chalking on a paint film surface?

Chalking is a phenomenon that occurs on the surface of paint films, particularly in exterior applications where coatings are exposed to ultraviolet (UV) light and weathering. The characteristic feature of chalking is that it forms a powdery deposit as the paint breaks down over time. This powder is primarily composed of the resin and pigment components of the paint, which have degraded due to exposure to the elements.

The presence of this powdery deposit indicates that the paint film is losing its binder and pigment, which can ultimately compromise the integrity of the coating. Chalking does not contribute positively to the visual appearance or protection offered by the coating; rather, it is an indication of wear and degradation. It does not enhance gloss, adhesion, or cracking resistance; on the contrary, excessive chalking can lead to problems such as reduced adhesion of subsequent coatings if they are applied over a chalked surface.

Understanding the mechanism of chalking is essential for coatings inspectors, as it informs decisions related to maintenance, repainting, and surface preparation for new coatings.