Prime or Not

[bluestringer]

I have been putting on a coat of primer on all my parts before painting, usually Rustoleum 2x grey. Today I painted a chassis with Createx Pearl paint without any primer first and I think it looks much better without the primer. If the parts are washed and prepped good before paint is primer even necessary? I know I've lost detail on some parts because of the primer. I'm thinking of going with no primer even on the body now. 

[Ace-Garageguy]

It depends entirely on what works consistently well for you.

I shoot primer on pretty much everything, because I usually end up doing work that will require a slight primer fill on every single part...like scraping parting lines, sanding and filling sink marks, etc.

And because I also inevitably do at least minimal bodywork, and because I painted real cars for years, and because I need maximum adhesion when I invariably wetsand and polish, I prime bodies as a matter of course.

But that's  just what works for me.   

Edited February 1, 2022 by Ace-Garageguy

[Rick L]

Grey primer brings out the flaws that Bill mentions that you would sometimes miss in the white plastic. Also primer helps the paint adhere. A thin coat is sufficient. You don’t need to lose detail by applying it like paint. If  you chose not to use primer, lacquer paint will adhere to styrene fine but some enamels may not, unless you sand it lightly. Washing the parts is also a good practice regardless of the paint used.

[Fat Brian]

When I mainly used Testor's enamels I didn't prime, the paint layer was thick enough on its own. Finding Duplicolor white primer changed my entire painting process. Now I use it on all my bodies because it's thin enough to not hide detail and it strips easily so I can paint with Tamiya or Duplicolor automotive paints and not ruin the body if it doesn't turn out the first time. I typically don't prime anything that's getting a flat finish though,  it doesn't seem necessary to me.

[Dpate]

2 hours ago, bluestringer said:

I have been putting on a coat of primer on all my parts before painting, usually Rustoleum 2x grey. Today I painted a chassis with Createx Pearl paint without any primer first and I think it looks much better without the primer. If the parts are washed and prepped good before paint is primer even necessary? I know I've lost detail on some parts because of the primer. I'm thinking of going with no primer even on the body now. 

Depends on the paint you use.  All the paint i use i need to use a primer or else it can attack the plastic.  If you use primer on parts you should be sanding it smooth or else it will look like BLAH_BLAH_BLAH_BLAH.  The primers i use are not thick primers pretty thin.  Rusto in a can i see how that can be thick and hide alot of detail.

[Plowboy]

I always primer everything. It does make a difference. 

[peteski]

I avoid primers as much as possible.  Since I mostly use plastic compatible (stinky) hobby paints, those adhere well to bare plastic.  I'm a firm believer that keeping the paint layer as thin as possible makes for better looking model.

But from what I read on the forum, if you use water-based (low-odor) paints, those do not adhere well to bare plastic, so primer is recommended.

[NOBLNG]

Fine script can be masked also to keep excess primer off of just that area.

[Skip]

Createx and other acrylic topcoats do not chemically bond with the primer (or plastic) basecoats, think of it as a "vinyl wrap" of sorts.  Acrylic paints adhere to the basecoat by basically "shrinking" onto a slick surface, primer/plastic by evaporating and "shrinking" onto the surface.  If that surface is too smooth, thinned, sprayed acrylic paint can actually bead up on the smooth surface leading to some really killer orange peel!

Think of using acrylic glue, like Elmer's Glue-All (white school glue), if you place it onto styrene/plastic/primer or another slick surface, it will sit there and evaporate until its dry to the touch.  Yet you can pick at the edges and peel the whole pool of glue off of the surface, the side "mating" to the body will be as smooth as the surface it was applied.  Now try to give it some tooth to adhere to the surface, by sanding and you will notice bits of primer come off with the glue blob.  The acrylic glue is pretty much a "really thick version of the acrylic paint", it needs tooth to adhere to the surface to stick.  You are providing that mechanical bond by sanding the surface for the acrylics in the paint to "mechanically' attach to, they will never bond because there is no chemical melting and bonding of the topcoat on primer.

Acrylic paints thinned and shot through an airbrush need a good toothy surface for a good mechanical bond, primer provides a good part of that, plus sanding the primed surface.  Acrylic paints shot through an airbrush will also show sanding scratches if you use too heavy of a grit when scuffing the surface.  I've used Red Scotchbrite pads or 800 - 1000 grit sandpapers with good luck, showing no sanding scratches and good mechanical adhesion.  (I haven't tried using any of the acrylic primers, in part because the lacquer-based primers are working well for what I'm doing.  There are some good YouTube videos out there covering the use of acrylic primers.)

Bottom line, you should use a good lacquer-based primer to help smooth over the sanding scratches from the earlier body work.  Then scuff the primer before shooting the acrylic paint over it.   Hope this helps.

Edited February 2, 2022 by Skip

[bluestringer]

Thanks guys. I will probably keep priming my bodies but not the small parts. 

[ZTony8]

I'll  prime if I've done any filling or puttying of parts where a join line shouldn't be visible. Otherwise ,no.

[rightrudder]

The Tamiya acrylics...kind of a hybrid in that they're alcohol-based--stick to bare plastic really well. I've done test panels where I haven't even scuffed the plastic, just a wash is dish soap, and the paint is locked down.

Fumes aren't too bad; they have a very sweet smell to them.

[slusher]

On 2/1/2022 at 11:47 PM, Plowboy said:

I always primer everything. It does make a difference. 

i prime everything even if it’s a thin coat. Parts I brush paint look better..

[Dave G.]

It's not that you primed but what you're using for primer. If you decant the 2x and thin it some then air brush it, your problem will go away. Not only is it too thick in the can but the can puts out too much paint. Thus you bury your detail. Heating your can of paint might mitigate the issue somewhat otherwise.

Ok, and while it's true that some stinky solvent paints do bond better than non stinky acrylic paints to plastic, non the less I've done the scratch tests and every paint I shot sticks all the better with even a thin primer coat first ( in fact my preference is one thin primer coat). Bar non, Tamiya acrylics, solvent lacquers, water based acrylics, craft paints and acrylics claimed to been enamels and true solvent based enamels were all tested over a year or so of random testing as the spirit led me. The bond to bare plastic is sufficient with many stinky solvent based paints and basically non existent with many acrylics shot to bare plastic, that is true. But the playing field is more level with primer added. Both solvent paints and water based acrylics gained substantial bond with primer on the surface. It's the same in 1/1 incidentally. It just is, anyone is free to assert otherwise but I've taken the time to do the tests. Both scratching tests and straight pull tests with blue painters tape, which is stronger bonding than model tapes.

The primer used in all testing was Badger Stynylrez. If you scuff both the model and the primer coat the bond is stronger yet but it is still very good even not scuffed.. And there is absolutely no bonding fear when taping even craft paints for two tone paint jobs using model tapes or de-tacked painters tape if everything was clean. All tests were washed first with odorless mineral spirits. By the way one lacquer did not fare well in scratching, though did ok with tape. That was LA Colors black nail polish. So all lacquers are not created equally.