Techniques · Finish
Priming problems: frosted, grainy or tacky primer and how to avoid them
Spray primer that goes on chalky, gritty or sticky is almost always a weather or technique problem. This explains the causes, the conditions to aim for, and what to do with a model that has already gone wrong.
What goes wrong and why
Aerosol primer needs to land wet, so the droplets flow together into a smooth film. In damp or cold air, or when the can is held too far away, the solvent evaporates before the paint arrives and it lands as dry grains, giving a rough, sandpaper feel. Sprue and Brush identify humidity, cold and distance as the three causes.
The Army Painter's guidance links each symptom to a cause: a chalky, dull finish to moisture condensing into the coat; a gritty or spattered surface to a can that is too cold to atomise properly; and primer that stays tacky to trapped moisture or solvent in a cold, still room.
The conditions to aim for
The Army Painter recommends priming between 15°C and 27°C, with relative humidity between 40% and 60%. Below roughly 10°C, or above about 65% humidity, it advises switching to a brush-on or airbrush primer instead of a spray can.
Very hot conditions cause problems too: the primer can dry too fast and turn powdery.
A routine that avoids most problems
Warm a cold can by standing it in warm, not hot, water for a few minutes. Never put it near a heater.
Shake it for at least a full minute.
Test on scrap card or a spare sprue before the model. It takes seconds and shows a bad day before it costs you a model.
Hold the can about 15 to 20 cm away (Army Painter's figure) and keep it moving in short passes, starting and stopping off the model.
Build up several thin coats rather than one heavy one. Thick coats fill fine detail.
Rescuing a bad coat
Light grain can sometimes be knocked back with a soft brush or very fine abrasive pad, then re-primed thinly.
Heavy fuzz, or primer still sticky after a full day, needs stripping and re-priming. Painting over a bad primer coat only hides the problem until the paint flakes.
No dry day in sight
Brush-on primer cures reliably indoors and needs no spray booth. It is slower, so apply it thinly and let it level. See also the Your first coat of primer guide for the basics.