Salt spray test

A classification of the corrosivity of an atmospheric environment towards steel and zinc, defined in ISO 12944 and ISO 9223 as categories C1 to C5 plus CX for extreme environments, with separate categories for immersed conditions. It is the starting point for selecting a protective coating system and its target durability.

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.

The thickness of a coating measured after it has dried or cured, usually specified per coat and for the complete system. It is a key quality control parameter, checked non-destructively on metal substrates with magnetic induction or eddy current gauges.

Laboratory exposure of materials to intensified ultraviolet light, moisture and heat cycles, using fluorescent UV or xenon arc apparatus, to simulate outdoor weathering in a compressed timescale. Methods are standardised in the ISO 4892 and ASTM G154 and G155 series, and results are used to compare colour retention, gloss loss, chalking and embrittlement of coatings, membranes and composites.

A preparatory coating applied to a substrate before an adhesive, sealant, coating or waterproofing membrane, improving adhesion by sealing porosity, binding dust or providing a chemically compatible surface. Primer selection depends on both the substrate and the product to be applied over it.