Coating

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.

The final coat of a coating system, providing the specified colour, gloss and resistance to weathering, ultraviolet light and chemical exposure. It is the system's first line of defence against the environment and largely determines how the finish looks over time.

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.

A coating that protects primarily by impermeability, isolating the substrate from water, oxygen and dissolved ions rather than by galvanic or inhibitive action. High build epoxies and coatings pigmented with lamellar materials such as micaceous iron oxide or glass flake are typical examples.

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.