Priming Serves 3 Purposes:
- It highlights imperfections like seams and makes it easier to see where they are and to fix them. If you can no longer see the imperfection after a fresh priming, you’ve adequately cleaned it up.
- Primers etch the plastic and give the color coats something to adhere to. Plastic is generally very smooth (unless you’ve sanded it) and some paints don’t stick as well as others.
- A primer can give the model a uniform undercoat or base. This means colors will look uniform when applied over them.
Do I have to Prime?
Strictly speaking, no.
Should I prime?
Generally, yes.
When can I skip priming?
- When using lacquers the paint is hot enough to etch the plastic on its own, therefore a primer can be skipped or you can use your first color as the base coat to act like a primer. Most model sprays in a rattle can are usually lacquer. Using a lacquer thinner with your paint through an airbrush is the same. Just remember that not all paints (like Vallejo Model Color) are compatible with lacquer thinners.
- Tiny parts. It may help to see imperfections like mold lines though.
When should I prime?
In theory at any time but best practice is to prime just before you paint the color coats so that you can verify the seams are clean and hidden, you have that uniform base for the color, and something for the color to stick to. Priming on the sprue can certainly be an option but usually it means extra effort as the modeler has to remove primer from the cement joins and likely prime again to verify a clean seam.
Can I use a DIY store primer?
These can be cheaper than higher quality modeling specific primers so look like an attractive option. With experience you can learn to use DIY store rattle cans for priming and painting, however most first time users apply the primer or paint too thick and because the chemicals used are so hot, it literally melts the plastic. The model can look like a blob or just lack details.
What color primer should I use?
That depends. A silver makes a good metal look for later chipping down to the metal. A color like red oxide used in some tanks or a yellow-green used on aircraft is also good to show wear through the color coats. If not doing much weathering, a gray is usually best. If the color coat will be gray, then either a black or white primer works best. If the color will be metallics like aluminum, steel, or those kinds of paints, usually a glossy black base helps to make them look almost chrome like. For schemes that have a lot of white, yellow, or red I like to use white as my primer.
What is Greenshirt’s preference?
My first choice in a primer is Mr Surfacer 1500 (sometimes 1000 or even 500 if the surface needs help), thinned 1:1 with Mr Color Leveling Thinner and sprayed through my Iwata Eclipse using a 0.3mm needle and about 15-20psi. If a larger model like a 4 engined bomber I’ll use a larger needle for better coverage.
As a second choice any Tamiya or Mr Surfacer primers from a rattle can work just as well, but tend to be a bit wasteful.
I do have some Vallejo primers and these work well enough but only if I use Vallejo’s airbrush thinner. However, as a primer it does not sand very well so is not as good for filling imperfections like Mr Surfacer. Which is why it is not my first choice.
I’m also trying the Mission Models Paint line of primers. They don’t quite seem like an etching primer but they do go on nicely once I’ve figured out the primer + thinner + polyurethane ratio. This is still a work in progress and at a future time I’ll publish my experience.