Paint experts, chime in please

[BadgerDave]

I'm about to attempt something I've never done before - painting a set of hard plastic saddlebags (a.k.a. Panniers or system cases) for a BMW motorcycle. I found a source in the UK for the extremely hard to find BMW Atlantic Blue Metallic paint in aerosol rattle cans, and ordered two types of primer as well. They call them "self etching" and "high fill".

The cases have a lightly pebbled surface with a slight sheen. My plan is to knock down the sheen and level the surface slightly with sandpaper, apply the etching primer, follow with the high fill primer, hit them with several light coats of color, and finish with gloss clear coats.

I'm not sure about sanding between the steps. My guess is that sanding isn't required after the primer coats, right? What about between color coats or interim clear coats? Or do I sand and polish only after the final clear coat?

I've also heard that it's a good idea to immediately follow color coats with a heat gun to lightly "melt in" the finish. Does that make sense?

Any other warnings or tips?

Thanks

[Jeff R]

My plan is to knock down the sheen and level the surface slightly with sandpaper, apply the etching primer, follow with the high fill primer, hit them with several light coats of color, and finish with gloss clear coats.

... and to replace the buckles/clasps with circa '74 Radarange knobs.

The real question is how to functionally replace the clutch pedal with a Bigsby. I don't know a lot about bikes, but I know both the clutch and the Bigsby are spring-loaded. This is doable.

[Stike]

I'm not real experienced in painting on plastics. If the pieces aren't painted but a colored plastic I would say wash it well with soap and hot water to get rid of any residue left from the molding process.

Your planned schedule sounds about right. Try giving the high build primer a good level sanding (320-400 grit range) then shoot a thin primer/sealer followed by your color coats and then clear allowing time for solvents to flash off between coats, no sanding.

[cynic]

Be sure not to run them into those damned yellow posts at the gas station once you've finished them.

I don't remember ever doing it with my standard system cases, but I know I did it several times with the extended lids I used when traveling on my old RT.

[LadyScary]

use a flex-agent in your base coat and clearcoat

[Hamer Dave]

use a flex-agent in your base coat and clearcoat

I was going to bring the subject of contraction/expansion as well. Not sure how the plastic will react to heat/cold, vibration, etc. I know they use a different mix with flexibility on the bumpers of my Ford. If you don't use the right formula, the finish will crack. At least on a Ford bumper!

[zenmindbeginner]

Use paint designed for vinyl... they are basically spray on dyes that actually become part of the vinyl, plastic or leather.

Vastly superior to painting on plastic which is usually a bad idea. The vinyl dye is the shit.

Just search under vinyl dye and you'll find loads of information.

[Punkavenger]

I always use XIM spray clear primer for a base coat. Sticks to anything ... tile, glass etc.

I always sand in between every coat, albiet very lightly and use a tack cloth

Read the directions on the spray cans especially regarding dry times ... sometimes the paint will wrinkle if you recoat either too soon or too late

Have a test spot or piece to make sure all products are compatible and actually bond to the original surface