Priming

I prime everything using MM flat white enamel regardless if the final coat is to be enamel or acrylic or if hand painting or using the airbrush.  Prior to priming, I throughly wipe all of the components down with rubbing alcohol and an old paint brush and let them air dry.  The only exception is when I'm using Alclad II for the final coat.  Then I prime with Krylon black lacquer per Matt Swann's recommendations (although I've read where people have had success priming with Future before using Alclad).

If the components are properly cleaned, you should never have any problems with the paint lifting when masking.

Always? No... (Of course, the Paint Nazis will tell you different...)  A wash of soap & water to remove the mold release agent from the parts is recomended, but I've never bothered with it unless it's visible or I can feel it, with exception of car bodies.  A quick wipe-down with rubbing alcohol or clean thinner works for me.  On the main exterior parts, like hulls, turrets, fuselages, wings, and car/truck bodies, you might want to give 'em a quick clean-up, or you might get a bunch of bubbles in the finish from silicone contamination.  I paint interiors and figures with brushes, same with exterior detail parts. 

The only priming I do is on figures I'm going to paint with Tamiya acryllics, since they have a tendency to streak, or when the plastic is a dark color... Gray, white, yellow, & silver plastics I don't usually prime.  When I DO prime, I use a light gray from Wal-Mart or some such.  Primer-surfacers are good for large model exteriors, since the primer will fill sanding scratches.  Just give primer-surfacer a good rub-down with a Scotch-brite pad and wipe the dust off before you paint.  I also prime armor that's molded in dark colors a light coat of light grey if I'm going to airbrush, since airbrushes put thinner coats of paint on the surface than a rattle-can. 

But, the bottom line is, "When in doubt, wash it out"...

I always prime, but not necessarily for the purpose of painting. Mainly, I use primer to find surface defects that don't show well on bare plastic.

That being said, some finish coats almost require priming: white, yellow, orange, red, and some specialized metallics.

white: undercoat with silver

yellow: undercoat with silver or white, or both

orange: same as yellow unless you want a slightly darker shade, in which case use a brown.

red: undercoat with white unless you want a slightly darker shade, in which case use a brown. 

<goose-steps quietly off stage, left>

OK, so you primer with say - gray Rustoleum auto primer as I have -  and you find surface defects. What would you usually use the correct them before paint? And do you re-primer before final paint then?

What Hans said.

You primed with Rustoleum and you can still see surface detail???!!! Auto primers tend to form fairly thick coatings, as they are meant to be sanded and contain relatively coarse pigments.

You must have a light touch!

Triarius -  what are you saying - that I should not use Rustoleum as the primer? I want the surface detail/scribe lines left on an aircraft- yes? 

Ok by me, but what is best? I read folks talking about some gray primer at Walmart? What is that?

YMMV, or De gustibus non disputandem est. What works for one may not work for another.

I wouldn't use a rattle can of automotive primer, at least not the Rustoleum. I did try this—the coating thickness was about five times that of a solid color coat of Tamiya Sky Gray, XF-19—as a primer, I consider Rustoleum auto primer a great filler. I then sanded it progressively to 1000 grit. Got a beautiful smooth surface. Then I tried to sand through it to bare plastic—it took almost an hour with 360 grit.

I use acrylics almost exclusively. For primers, I use either the above Tamiya or any Polly Scale light gray.

For enamels, I'd recommend a high quality flat light gray for general purpose use. As I've mentioned elsewhere, whites should be undercoated with silver, yellows and oranges with white or silver and white, and reds with white (bright reds) or brown (dark reds).

Thanks for the "primer" on "primers"! 

Think I will take back the Rustoleum to Lowes and head for Walmart.

BTW, I am using the rattle can of white Tamiya surface primer and it sure does bring out the defects I missed. Lots of work to do with green putty - sure wish I had the Liquid Surface Primer. Next time! 

Jake, try 3M Acryl Blue, Green or Red. Thin them with 90% isopropyl when needed. I've just been told on another forum that Blue is finest and slowest drying, green in the middle, and red the coarsest and fastest drying. I don't see a lot of difference in grain size between blue and red, and either will produce a glasslike surface if sufficiently sanded and polished.

Also, learn the technique of using medium thickness or gap filling CA as a filler. It's much faster because the drying time is much less. 

Ross - I have used some thicker CA for gaps and it seems OK but seems more difficult to sand??  

I assume you mean 3M Acryls for a primer?

Thanks for all your time!

No, the 3M Acryls are automotive filler putties.

With CA as a filler, you have to start sanding just as soon as it sets—a matter of minutes. If you wait longer, it gets much harder than styrene. 

Ross - OK 3M Acryl auto filler putties - found at most auto parts stores? You use it instead of Squadron Green Putty?

Thanks for the tip on CA sanding!

Look for auto body stores, although some auto parts places carry them. Stores that cater to body work are also the best places to get your wet-or-dry sandpaper. I do not recommend Pep Boys for this stuff, but it's worth looking at Wal Mart.

I tried Squadron Green putty once. I threw most of the tube out. I've heard good things about the Tamiya putties, but as I've said before, at least elsewhere, one tube of Acryl Blue will last a lifetime with proper care. Decant (detube ) small amounts into a hobby paint bottle with a foil lid liner, and use that when modeling. Keep the rest of the tube in a heavy zip-lock bag in a cool place. If the cap on the tube cracks, replace with a toothpaste tube cap.

You're welcome!

Happy Styrene!

I have yet to find the 3M but I will tell you that I tried Hans' suggestion of wetting my finger with isopropyl alcohol and then applying green putty and it really helps!

But I will find the 3M for the next project! Thanks.