Accelerated weathering

The breakdown of polymer surfaces by ultraviolet radiation, causing chalking, discolouration, embrittlement and loss of gloss. Exposed resins, membranes and coatings are protected with UV stabilisers, pigmented gelcoats or sacrificial surface layers.

A coating defect in which ultraviolet degradation of the binder at the surface leaves a loosely bound, powdery layer of pigment that can be rubbed off. It is a normal long term weathering mode of many exterior coatings and is more pronounced in binders with poor ultraviolet resistance.

An accelerated laboratory corrosion test in which coated or plated specimens are exposed to a fine fog of salt solution in a closed chamber under standardised conditions, as described in ISO 9227 and ASTM B117. Results are used for comparative and quality control purposes, as correlation with service life in real atmospheres is limited.

The gradual change in the appearance and properties of a material caused by outdoor exposure to ultraviolet radiation, moisture, temperature cycling and airborne pollutants. Coating and material durability is assessed by natural exposure trials and by accelerated weathering tests in the laboratory.