About rust and stencils

[AccDossNumber15]

There's a metallic PC part I'd like to paint, but:

1. It has some minor rust and corrosion on it, some patches are a bit coarse, so should I use some ketchup then sand it from grit 300 to 1500 to smoothen it out?
   • I'm going for a matte finish so it might affect the appearance
2. Do I also need multiple passes when applying a stencil on my primary coat?

[Needfuldoer]

51 minutes ago, AccDossNumber15 said:

ketchup

What?

 

Just put a folded-up paper towel over the rust spot, then soak it with white vinegar. Vinegar is an ingredient in ketchup, and its acetic acid is the only thing in ketchup that will actually do anything to the rust. Might as well use straight vinegar, which will have more acid in it for the same volume.

 

A specialty product like Evapo-Rust would work better, but that's just something else you'd need to buy. CLR might help too.

 

You're not going to fix the rough pitted surface by just sanding. (That only "works" when you can sand all the material down to the depth of the bottom of the worst pit.) To fill that you'll want to use some kind of high-build primer, then sand that smooth, and then finally top coat.

 

51 minutes ago, AccDossNumber15 said:

Do I also need multiple passes when applying a stencil on my primary coat?

That's easier than trying to put on a heavy coat of spray paint without causing runs or overspray around the stencil. (Unless "paint runs and overspray" is the look you're after, in which case go nuts with it.)

[TPCEA]

Adding to the great info from @Needfuldoer, apply a thin spray of paint, and do not remove the stencil. Let dry. Repeat until you are satisfied with the results. Remove the stencil and touch up.