Primer

The surface onto which a coating, membrane, adhesive or covering is applied. In roofing this may be the structural deck, insulation, screed or an existing waterproofing layer; substrate condition, priming and compatibility govern adhesion and long-term performance.

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.

The ability of a liquid adhesive, resin or coating to spread over and make intimate contact with a substrate or fibre surface. Good wetting is essential for adhesion and for full fibre impregnation in composites, and depends on the relative surface energies of the liquid and substrate and on surface cleanliness.

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.

A primer containing a high loading of metallic zinc dust in an organic binder, usually epoxy, or an inorganic silicate binder, providing galvanic protection to steel in a similar way to galvanising. It requires a high standard of blast cleaned surface so that the zinc makes electrical contact with the steel.

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.