Why has my spray paint gone rough, powdery or frosty?

An aerosol produces a fine mist of paint that has to stay wet long enough to reach the surface and flow together into a film. Almost every rough spray finish is that mist arriving dry, or arriving with water in it. Neither problem is in the tin, which is why people replace the paint and get the same result.

Safety

What you'll need

• A bowl of hand-hot water
• Fine wet-and-dry paper and a polishing cloth (optional)
• Somewhere warm, dry and still to spray and to cure

Step by step

1. Identify which fault you have.Rough, gritty, matt and pale where it should be glossy is dry spray. A milky or white haze in the film, worst in the thickest areas, is blooming from humidity. Orange-peel texture with the gloss intact is a wet-but-not-levelling problem. Runs are simply too much paint.
2. Check the temperature of the can, not just the room.Propellant expanding out of a cold can chills the paint further, so the droplets are already too viscous to flow when they land. Stand the can in hand-hot tap water for a few minutes. Never on a radiator, on a hob or in a microwave.
3. Check the temperature of what you are spraying onto.A model that has been in a cold garage stays cold long after the room warms up, and the paint chills on contact. Bring the model in for an hour before you start.
4. Shake for the time the label says.Which is usually one to two minutes after the ball starts rattling, and almost nobody does it. Under-mixed paint sprays medium first and pigment later, and lands rough.
5. Move closer.The single most common cause. About a hand span, twenty to twenty-five centimetres for most model cans. Further than that and the solvent flashes off in flight, so half-dry droplets land and pack rather than flow.
6. Watch the humidity.Spraying on a damp or muggy day, or straight after rain, condenses moisture into the cooling wet film and turns it milky. That is water, not paint. If the air is wet, do something else that day.
7. Spray thin passes with the stroke starting and finishing off the model.Press the button before the can is over the work and release after it has passed, so the spitting that happens at the start and end of a burst does not land on the model. Overlap each pass by about half.
8. Recover the finish once it is fully cured.Dry spray and orange peel can usually be sanded flat with a fine wet-and-dry paper and either polished or oversprayed with a further light coat in better conditions. Blooming sometimes clears with a very light wet coat that re-dissolves the film — otherwise it needs stripping.

Tips

• Do a test pass on a scrap card or an old sprue every single time before the can points at the model. It costs two seconds and catches a blocked nozzle, an unshaken can and a cold can.
• Invert the can and spray until only propellant comes out when you finish. It clears the nozzle, and a blocked nozzle is the other main source of spatter.
• British weather rarely gives you a warm dry still day when you want one. A garage with the door open and a fan heater on beforehand, turned off while you spray, is the usual workaround.

Common mistakes

• Trying to fix dry spray by spraying more — Another coat of dry mist lands on top of the first and packs the texture deeper. Each attempt makes the surface rougher and thicker until detail is lost and it needs stripping.
• Spraying in a cold garage in winter — Below roughly ten degrees most aerosol paint will not flow out, whatever you do with technique. This is the reason for the great majority of ruined winter paint jobs.
• Sanding a rough coat while it is still soft — It clogs the paper instantly and drags the film into ridges. Give it days rather than hours before sanding a spray finish.

If it doesn't work

Questions people ask