Composite
Application of FR4-45, FRS30 or FR-P1K filler
Plastic
It depends on different parameters:
Is the color of the substrate close to the topcoat color? Does the plastic present pinholes ; parting lines or textured surface you need to get rid of?
If the answer to one of these question is yes, then a filler such as FR4-45 is needed.
If not, you can apply the topcoat directly on this plastic (after ensuring their good adhesion and compatibility.)
Aluminium
Application of F69 epoxy primer.
Primer must be cured at least at 40 °C before topcoat application. See F69 TDS for further details.