mechanical adhesion can be obtained by blending an inorganic filler such as a pigment which has a particle size that will result in a rough surface when the primer is applied and baked to the extruded and ground powder coating one example of such a pigment is an aluminum flake that has been bonded to the powder base coat in this way when the resulting powder primer is applied to a metal substrate and cured followed by application of the powder top coat and cured the bond between the base and the top coat are strong enough to pass subjection to boiling water cross hatch and adhesion tape testing however by itself the coating prepared in this manner will fail intercoat adhesion when tested by the standard post boiling water finger nail adhesion test the second approach to improve intercoat adhesion is to blend a powder that is to comprise the base coat that may comprise fep pfa and mfa of a particle size similar to that of the topcoat that is to be applied to the base coat this promotes a much tighter bond between the base and the topcoat by means of chemical and mechanical bonds adhesion of base and top coat are improved to the point that the resulting coating passes boiling water cross hatch and tape test as well as the finger nail test which is very important for most of industrial applications such as in coatings for commercial bake ware one or both of the.