Blistering

Separation of the plies within a laminate, caused by impact, manufacturing defects, fatigue or moisture ingress. Because it can spread unseen beneath an undamaged surface and sharply reduces compressive strength, delamination is a primary target of non-destructive inspection.

A discontinuity in a protective coating, such as a pinhole, void, crack or excessively thin spot, that exposes the substrate to the environment. Holidays are located with low voltage wet sponge or high voltage spark test instruments, particularly on pipeline coatings and tank linings.

A standardised description of the visual cleanliness of a steel surface before painting, defined in ISO 8501-1 as Sa grades for blast cleaned steel and St grades for hand and power tool cleaned steel. Coating specifications state the required preparation grade because coating life depends heavily on surface preparation.

A material applied as a very thin layer, or added to a formulation, to improve the bond between a coating or adhesive and a difficult substrate. Examples include silane coupling agents for glass and metals and chlorinated polyolefins for low surface energy plastics such as polypropylene.