Runs (or drips/sags) are streaks of paint that have flowed downward on a vertical surface under the influence of gravity, creating a teardrop or curtain shape. They happen when too much paint is applied in one area — typically by holding the airbrush too close, moving too slowly, or making too many passes without allowing drying time.
Prevention:
- Keep the airbrush moving — never stop over the surface with paint flowing.
- Build coverage in multiple thin layers rather than one heavy coat.
- Allow each layer to dry (or at least become touch-dry) before the next pass.
- Work at a consistent distance — 5–10cm for most work.
Fixing a run: On acrylic paint, if caught while still wet, you may be able to blend it out with a very light pass from a distance. Once dry, the run must either be sanded (on hard surfaces) or accepted. On models, a run can sometimes be carefully scraped with a blade and re-primed.
Related: Overspray · PSI · Trigger Control