primers designed for painting plastics are not water based. An important point for choosing a primer for plastic is making sure the primer's propellant or solvent will not dissolve or warp the plastic part itself (e.g. most common household spray paint will damage polystyrene foam). For this reason, most manufacturers recommend that both the primer and paint should be tested on a less visible location of the part being painted. Alternatives Alternative surface treatments, such as plasma activation, can replace primers in the cases when the latter are used to improve adhesive bonding between the substrate and the paint or the lacquer. Quality of the adhesive bonding, such as varnishing and painting, depends strongly on the ability of the adhesive to efficiently cover (wet) the substrate area. This happens when the surface energy of the substrate is greater than the surface energy of the adhesive. However, high strength adhesives – lacquers and paints – have high surface energy. Thus, their application is problematic for low surface energy materials such as polymers or oxidized metals. To solve this problem, plasma activation is used as a preparation step before adhesive bonding. It cleans the polymer surface from the organic contaminants, removes a weak boundary layer, strengthens the surface by cross-linking polymer molecules and chemically bonds to the substrate a strong layer with high surface energy and chemical affinity to the adhesive. Moreover, plasma processing can also reduce or remove hard oxides from metal surfaces, enabling painting and gluing of metals such as copper and aluminum. Importantly, plasma activation can be performed at the atmospheric pressure in air with fast processing speeds. It does not use wet chemistry, which positively affects its costs, safety and environmental impact. See also Paint Aerosol paint Gesso Stain-blocking primer References Paints Wood finishing materials Metalworking