CSLB C-33 Painting & DecoratingCoating ApplicationMedium
A painting contractor is applying a fast-drying, solvent-borne epoxy coating to a steel beam in a fabrication shop. The application is done using an airless sprayer. The contractor notices that some of the coating particles are drying in the air before reaching the substrate, resulting in a rough, sandy texture on the surface. What is this defect called, and what is a common cause?
- AOrange peel; caused by improper spray gun settings.
- BCratering; caused by surface contamination.
- CBlushing; caused by high humidity.
- DDry spray; caused by spraying too far from the substrate.
Show answer & explanationAnswer & explanation
Correct answer: D. Dry spray; caused by spraying too far from the substrate.
The description of coating particles drying in the air before reaching the surface, resulting in a rough, sandy texture, is characteristic of 'dry spray' or 'overspray'. This often occurs when the spray gun is held too far from the substrate, allowing solvents to evaporate excessively during transit, or when the material is atomized too finely, or the air flow is too high.
Why the other options are wrong
- A. Orange peel is a textured surface resembling an orange peel, usually due to poor atomization, incorrect viscosity, or improper spray technique, but not particles drying in the air.
- B. Cratering (or fisheyes) are small, circular depressions caused by surface contamination, not a rough texture from dried particles.
- C. Blushing is a milky or hazy appearance, typically caused by high humidity or rapid solvent evaporation, not a rough, sandy texture.
Dry Spray / Overspray
Dry spray occurs when coating particles dry in the air before reaching the substrate, resulting in a rough, sandy, or dusty film, often due to excessive spray distance, high air pressure, or fast-drying solvents.
- Creates a poor aesthetic and reduced film integrity.
- Common causes: spraying too far, high air pressure, fast solvents, low ambient temperature.
- Correction involves adjusting spray distance, pressure, or using slower solvents.
Memory trick: Too far, too fast, makes the paint dry, leaving dust at last.