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