Is it necessary to prime your plastic models before painting? That’s a question that pops up a lot in the model-building community.
There’s no one-size-fits-all answer.
Priming your model is not explicitly required. However, it can be incredibly helpful and can save you from having to strip and repaint a model multiple times, due to paint adhesion issues or other imperfections.
Let’s dive deeper into the benefits of priming your models before painting.
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What’s the point of primer anyway?
Primer is a layer of paint that is sprayed onto the model before laying the final colors.
Its purpose is to provide a uniform smooth surface for the paint to adhere to because some paints don’t stick to plastic all that well.
The primer may also help to fill in small imperfections on the surface of the model. These imperfections could be tiny scratches created by sanding the model, defects from molding, or perhaps thin seam lines that you didn’t fill properly.
If the primer doesn’t fill these imperfections, it will at least make them very easy to spot allowing you to correct them before committing to the final paint job.
The primer can also act as a “sealant” or barrier coat of paint to protect the surface from the potentially damaging effects of some types of paint.
Some lacquer-based paints such as the Mr. Paint line may damage the plastic when applied too heavily. The primer offers a bit of protection for the plastic from this kind of damage. Although, if you manage to dump too much lacquer paint on the model, even the primer won’t be able to protect it.
When should you consider using a primer?
Priming is not always needed and many model builders skip this step. It is a personal choice.
I prime pretty much everything even though I am using durable lacquer paints such as Gunze Mr. Color and Tamiya LP.
So what are some of the scenarios where primer comes in handy?
Water-based paints
Water-based acrylic paints such as Vallejo don’t like to stick to bare plastic at all. Priming will help the paint adhere better and avoid flaking off later on.
Multi-colored model parts
Some model kits come with parts molded in different colors. Examples of such a kit would be the Academy’s 1/48 F-4J Phantom II or Academy’s Titanic kits. Some parts may be white, while others will be black or grey.
If you don’t prime kits like these, the tonal differences between the parts will be either very noticeable or require numerous layers of paint to blend them.
Priming will create a uniform surface that’s easier to paint.
Metal finish
Achieving a realistic-looking metal finish usually requires a gloss-black primer layer to build upon. Otherwise, the metal will look flat and unconvincing.
You don’t necessarily need any special primer for this purpose though. In fact, a good gloss black paint such as the Mr. Color GX2 is a perfect choice for this purpose.
Is the color of the primer important?
Choosing the right color for your primer may be the difference between a total nightmare and an absolute breeze when trying to achieve a realistic-looking finish.
The most used primer colors are grey, white, and black.
They all have their advantages.
Grey primer works great for creating a neutral base that you can use to paint both light and dark colors.
White primer is great when you need to paint the model with brighter colors.
Black primer can be used to employ advanced techniques such as black basing that experienced model builders use to create a realistic and weathered look.
Apart from these three, there are of course other colors available and you can even mix them to your liking.
TIP: Red and yellow paints are notorious for being very transparent. Trying to paint something yellow over black primer will be an exercise in futility. White primer works best for yellows and pink or yellow primer works best for reds.
Surface preparation before priming
Before you dive into priming, it’s important to make sure the model or model part:
- is clean
- is free of dust particles
Both conditions are essential for getting a good finish and the best-possible adhesion.
Grease
The model parts can be a bit greasy either because of the mold release agent used in the manufacturing process or because of the grease that’s naturally present on your fingertips.
To get rid of the mold-release residue, some modelers prefer to wash all the sprues in soapy water. I usually skip this step and never had a problem.
Grease from fingertips can be a problem though and I usually wipe the model down with a piece of lint-free cloth dampened with isopropyl alcohol. The best solution is prevention though and it’s easily achieved by using rubber gloves when handling the model and its parts.
Dust
There are two types of dust in the model building world – the dust that is ever-present in our homes and the dust we create during the building process – usually the side effect of sanding.
If you don’t clean the model before priming, these micro-particles will be sealed in and may become fairly noticeable. The primer may also not stick to the surface properly.
To get rid of the dust, use a slightly damp cloth or piece of paper towel and wipe down the model’s surface. To remove dust from panel lines, I usually use an old soft toothbrush.
How to apply the primer?
Primers are most often applied using:
- an airbrush
- a spray can
Primers meant for airbrush application will come in a small bottle. Sometimes they are ready to use, but in some cases, you might need to thin them with a specific thinner. I tend to use Mr. Color Leveling Thinner to both thin my primers and my paints.
Spray primers come in an aerosol can and are ready to use. They are usually slightly more expensive than airbrush primers and you have much less control over the application process. But if you don’t have an airbrush or if you need to prime a large model, the rattle can primers are your best choice. Just don’t use them inside your house, please.
Can you apply a primer with a paintbrush? Technically, there’s nothing stopping you from trying to apply the primer with a paintbrush. But it’s not going to work very well. You will most likely end up with an uneven finish.
Even if you are painting your model with paintbrushes, do yourself a favor, and prime the model with a spray can primer.
How should your primer layer look?
The finished primer layer may look slightly different depending on the type of primer you used.
In general, the surface should be smooth with a satin or slightly glossy look. There should not be any dusty-looking spots on the model. The orange peel look is also a sign you didn’t apply the primer properly.
If you are not happy with the look of your primed model, you can always strip the paint and try it again. Or you can try to smoothen the not-so-good-looking spots with fine-grit sandpaper.