Spray painting plastic from an aerosol can has rules of its own. They concern the choice of materials and the surface preparation above all. Here is the job step by step.
Which plastics can be painted and which cannot?
Parts made of polyethylene, PTFE, silicone and polypropylene are almost impossible to paint – the paint either does not lay down at all or holds very poorly. Most other plastics can be painted. Keep in mind, though, that there are tens of thousands of different plastics and some of them can surprise you. So if you are dealing with an unfamiliar material for the first time, spray a test patch on a small area first.
Surface preparation. Priming
If the plastic is hard enough, scuff the surface with an abrasive pad first. Adhesion to a dull surface is always better than to a glossy one. The choice of primer depends on the type of paint you are going to apply to the plastic and on the condition of the surface.
If you are going to use an acrylic paint or a primer-enamel, you can do without the adhesive activator KU-6000 – acrylic materials have good adhesion to plastics and stay flexible. Using the adhesive activator will not spoil anything, it will only improve the result further. The activator is applied in one thin coat.
If you are going to use alkyd paints, the adhesive activator KU-6000 becomes mandatory. Without it the adhesion of alkyd materials to plastic is low. Alkyd paints are also less flexible, so use them on plastic only when there is no alternative – for example, when the coating has to withstand solvents and abrasion.
If the surface has minor defects – scratches or other shallow damage – apply the acrylic filler primer KU-220X or the universal acrylic primer KU-210X in a fairly thick coat. Once the filler primer has dried, sand it with fine sandpaper.
Applying the paint – spraying
Plastic surfaces can be painted with acrylic, alkyd and cellulose-based paints (the automotive metallic base coat). Start, however, with the primer-enamel for plastic KU-60XX. As its name says, it can be used both as a primer and as a topcoat. It goes straight onto the plastic in several coats (over the adhesive activator or over an acrylic primer as well). That is all – a matt finish in one of the RAL colors is ready. If the color range of the primer-enamel has no suitable shade, you can apply the paint you like most over it.
Acrylic materials suit plastic best: the universal fast-drying high-gloss and matt RAL paint KU-AXXXX and the satin paint SATIN RAL.
Acrylic metallics SILVER GRAIN FINISH, REFLECTIVE FINISH and MIRROR FINISH differ in the type of pigment (more about pigment types here), but all of them go onto a primed surface only. The primer is the acrylic KU-210X.
Alkyd paints in aerosol cans may be applied to plastic only over the adhesive activator KU-6000. Alkyd paints behave in their own way during application, drying and curing, so we recommend reading about them here first.
The cellulose-based metallic automotive repair paint also goes over an acrylic primer. Refinishing automotive plastic is covered in this article
The acrylic textured paint for plastic deserves a separate mention. It builds a relief finish – a texture that reproduces the original factory grain and hides unevenness and minor defects of the surface being painted. Start by choosing KU-6206 with a fine texture or KU-6207 with a coarse one. Then work out the distance from the can to the surface, the number of coats and the spraying technique so that the finish is indistinguishable from the factory one. The textured paint comes in black only, but it can be painted over if needed.
Topcoat – applying the clear coat
A clear coat is mandatory only over a cellulose-based automotive metallic. The best choice is the 1K acrylic automotive varnish KU-9010; the universal acrylic KU-9002 and KU-9004 (gloss and matt) can also be used.
Matt acrylic paints can be cleared for extra gloss and additional protection, but this is not mandatory.
Alkyd paint should not be cleared – it gives enough gloss on its own and is harder than an acrylic clear coat.
