How to Prime Miniatures Indoors

Why an aerosol is not an indoor option

People do spray primer in a bathroom with the window open, and it is worth being clear about what actually happens when you do.

An aerosol puts a cloud of fine solvent and pigment particles into the air. Most of it does not land on the model. It stays airborne for a long time, you breathe it, and the rest settles as a thin film on every surface in the room — including, over repeated sessions, visibly.

An open window does not meaningfully change that; it is not directional airflow. A bathroom extractor fan helps a little and does not solve it. This is a genuine ventilation problem rather than a fussiness one, and the fix is to not use the aerosol rather than to use it more carefully.

Brushing primer on: the technique

The one real pitfall is filling detail, because the instinct with primer is to cover in one confident coat. Two thin coats is the whole technique.

• Thin it slightly. Primer from the bottle is thick. A few drops of water on the palette makes it flow instead of dragging.
• Recesses first, raised areas second. Work primer into the crevices with the tip of the brush, then cover the flat surfaces. Doing it the other way round means flooding the recesses to reach them.
• First coat should be translucent. You should still see plastic through it. That is correct, not a mistake.
• Second coat brings it to opacity. Twenty minutes later.
• Use a brush you do not care about. Primer is hard on bristles. A retired synthetic is ideal — this is one of the jobs that retired brushes are for.

Realistically this takes a couple of minutes per infantry model, which is slower than an aerosol and faster than waiting three weeks for a dry weekend.

Airbrushing primer indoors

Better finish, more equipment. Thinner coats than any aerosol, full control, no weather dependency. The details are in the airbrush primer picks, but the indoor-specific points:

• You still need to deal with overspray. Water-based primer has mild fumes and it still produces airborne particles that settle on everything nearby. A spray booth ducted to a window is the answer, and it is the main reason to own one.
• A mask is sensible. Not strictly required for water-based acrylics; genuinely required for lacquer primers.
• Flush immediately. Primer dries hard inside a nozzle and is far more stubborn than paint. Water through while it is still wet, then a proper clean.

Setting up a space that works

Priming indoors is messier than painting indoors, so a few practical points:

• Cover the surface. Primer drips and it is designed to key hard to things. A sheet of card or an old towel.
• Work over a tray. Catches the model when you drop it, which you will.
• Use a handle. Holding a bare model while priming it means priming your fingers and leaving an unprimed patch. See painting handles.
• Prime in batches. A squad at a time, left overnight. Batching is what makes brush priming tolerable rather than tedious — the same principle as painting faster.

Things people suggest that you should not do

• Spraying in a cardboard box indoors. The box catches the droplets heading straight away from you. It does nothing about the cloud that comes back out of the open side, which is most of the problem.
• Using hairspray or craft sealant as primer. Neither provides mechanical key, both can go sticky in humidity, and you will be stripping the model.
• Skipping primer and relying on varnish. Varnish on top holds onto paint that is holding onto nothing, so damage takes the whole stack off together — see do you need to prime miniatures.
• Spraying in an unheated garage in winter. Technically outdoors, and cold air gives you the same gritty finish as damp air. See why primer goes grainy.