Primer is the layer that makes everything above it work. It gives acrylic paint a slightly textured surface to grip, it turns a multi-coloured model into a single neutral tone, and it reveals the surface flaws you want to find before you start painting rather than after.
It is also the step most likely to ruin a model outright. A grainy or thick primer coat cannot be painted over successfully, and stripping it back is far more work than priming carefully in the first place.
Primer is not the same as base paint
People sometimes brush a coat of ordinary paint on and call it primed. It is not the same thing. Primer is formulated to bond to bare plastic or resin and to leave a surface that acrylics key into. Ordinary base paint sits on top of smooth plastic without much mechanical grip, which is why unprimed models shed paint from raised edges after a few games.
Primer also does a job base paint cannot: it unifies a model built from different materials. A kit with plastic body, resin arms and a metal weapon has three surfaces that take paint differently. Primer makes them one.
Three ways to apply it
| Method | Strengths | Weaknesses |
|---|---|---|
| Aerosol spray | Fast, very thin even coats, excellent for batches | Weather and ventilation dependent, least control, easiest to overapply |
| Brush-on | Total control, works indoors year round, good for touch-ups and single models | Slow, can obscure fine detail if applied thickly, brush marks possible |
| Airbrush | Finest control of coverage and colour, ideal for zenithal work | Equipment cost, cleaning time, learning curve |
Most people use aerosol for the bulk of an army and keep a pot of brush-on primer for touch-ups and for days when spraying outdoors is not an option.
How much primer do you actually need?
Less than you think. The goal is a thin, even, matt layer that covers the plastic. It does not need to be opaque on the first pass, and it does not need to look finished.
The failure mode is trying to achieve full coverage in one go. A heavy coat pools in recesses, softens crisp edges and buries the fine detail you paid for. Detail lost under primer is lost permanently.
A useful test: after priming, you should still be able to see every panel line, rivet and fabric fold as clearly as you could on bare plastic. If anything looks softer, the coat is too thick.
Black, white or grey?
The primer colour changes how every subsequent layer behaves.
- Black gives instant shadow in every recess and makes a model look coherent quickly. Colours painted over it appear darker and more muted, and light colours need several coats to cover. Good for dark schemes and for fast tabletop painting.
- White makes colours appear brighter and more saturated, and light colours cover in fewer coats. It is unforgiving, because every gap in your painting shows as a white spot, and it can make a model look flat until shading goes on. Good for bright, light or high-saturation schemes.
- Grey is the compromise and the sensible default for a first army. Colours read close to how they look in the pot, coverage is reasonable in both directions, and mistakes are less glaring than on white.
Coloured primer
Priming directly in something close to your dominant colour saves the base-coating stage entirely. If your army is dark green, a dark green primer means the largest area of the model is already done. The trade-off is that you are committed, and touch-ups need that same colour.
Zenithal priming
A conceptual approach rather than a product. You prime the whole model dark, then spray a lighter colour from above at an angle, so the upper surfaces catch the light coat and the undersides stay dark. The result is a pre-shaded model with built-in light and shadow, which you then paint over with thinned or translucent colours so the underlying gradient shows through.
It rewards restraint. The second pass should be a suggestion of light, not a full recoat from above.
How to use spray primer
- Read the can. Manufacturers specify their own distances, drying times and conditions, and those instructions override any general advice including this article.
- Set up somewhere suitable. Aerosols require good ventilation. Outdoors or a well-ventilated space, away from anything you do not want overspray on, and follow the manufacturer's guidance on personal protection.
- Shake thoroughly. Longer than feels necessary, usually a minute or more after you hear the ball rattling freely. Under-shaken primer sprays unevenly and can go grainy.
- Test on something else first. A spare sprue or a piece of card. This tells you the spray pattern is even and the can is behaving before you point it at a model.
- Hold at the distance the can specifies. Too close floods the model; too far lets the primer partially dry in the air and land as powder.
- Use multiple light passes. Start the spray beside the model, sweep across, release after passing it. Never start or stop the spray while pointed at the model.
- Rotate between passes. Spray from several angles including slightly from below, so recesses and undersides get covered.
- Allow proper drying and curing. Touch-dry is not cured. Follow the manufacturer's stated time and give it longer if conditions are cool or damp.
Why primer goes grainy
Grainy or dusty primer is the most common failure, and it is almost always because the primer partially dried before it reached the model. Contributing factors:
- Spraying from too far away. The droplets lose solvent in flight and land as dry particles rather than a wet film.
- Environmental conditions. Cold, heat and humidity all affect how the spray behaves. Manufacturers state suitable conditions for their own products; use those figures rather than a generic rule, because they vary between formulations.
- Insufficient shaking. Poorly mixed propellant and pigment sprays inconsistently.
- Over-application. Counterintuitively, flooding a surface can also produce a rough finish as the excess skins over unevenly.
- An almost-empty can. Pressure drops and atomisation gets worse as a can empties.
A lightly grainy model can sometimes be rescued with very fine sanding on the flat areas followed by a thin brush-on coat. A heavily grainy one usually needs stripping.
Why primer goes glossy or thick
Gloss and pooling both point to too much primer arriving at once, usually from spraying too close or holding the spray in one place. The primer stays wet, runs into recesses and dries as a thick shiny film.
Unlike graininess, this one is unrecoverable in terms of detail. The fix is prevention: lighter passes, correct distance, keep the can moving.
Can you paint without primer?
You can, and the result depends on what you are painting and how it will be treated.
Some modern acrylic ranges are formulated to adhere reasonably to bare plastic, and a display model that never gets handled may be fine. For anything that will be picked up, transported or played with, primer is worth the extra step. Paint on unprimed plastic wears off raised edges first, which is exactly where the eye goes.
Resin and metal make it less optional. Both benefit substantially from a proper primer coat, and resin should be washed and dried first to remove mould release agent.
How long should primer dry?
Follow the manufacturer's stated time, because it varies significantly between products. There is no single universal figure, and the numbers people quote online are usually specific to whatever they happen to use.
Two practical points hold regardless. Touch-dry and fully cured are different states, and paint applied to primer that has not cured can lift later. And cool or damp conditions extend drying times, sometimes considerably, so give it longer than the minimum if the environment is not ideal.
Frequently asked questions
Should I prime before or after assembly?
Assemble first for simple models. Prime sub-assemblies separately where a component blocks access to detail behind it. Either way, remove mould lines before priming; our guide to removing mould lines explains why they become so visible once primer is on.
Can I brush primer over a spray coat?
Yes, and it is the standard way to fix missed spots and touch up areas you have sanded. Keep it thin and confine it to the area that needs it.
Do I need to wash models before priming?
For plastic it is optional but harmless, and it removes handling grease. For resin it is genuinely worth doing, because release agent left on the surface prevents primer bonding properly.
What if I prime the wrong colour?
Prime over it in the colour you wanted, keeping the coat thin. Two thin primer layers are still thinner than one heavy one, so this is usually recoverable without stripping.
Does primer colour affect how many coats of paint I need?
Substantially. Light colours over black primer can need four or five coats and still look patchy, while the same colour over white or grey may cover in two. Match the primer to the value of your dominant colour and you save a lot of work. Our guide to thinning paints properly covers how consistency interacts with coverage.
Is it worth priming in summer only?
Not necessarily, but conditions matter more than the calendar. If it is cold or damp where you spray, use brush-on primer instead rather than fighting the aerosol. A brush-primed model painted in December beats a grainy one sprayed in the wrong conditions. New painters may want to start with our beginner painting guide for the full sequence.
Independent guide published by Blubbercove Ltd/WarSplay. This article is not affiliated with, sponsored by, endorsed by, authorised by or licensed by Games Workshop Limited. Warhammer 40,000 is a trade mark of Games Workshop Limited.