CSLB C-33 Painting & DecoratingCoating ApplicationEasy
A painting crew is applying a high-build elastomeric coating to a stucco exterior using an airless sprayer. They notice that the spray pattern has 'fingers' or 'tails' (unatomized streaks) on the edges. Which of the following is the most likely cause of this issue?
- AThe spray tip is too large for the coating viscosity.
- BThe spray tip is worn out.
- CThe fluid pressure is set too high.
- DThe coating has been over-thinned.
Show answer & explanationAnswer & explanation
Correct answer: B. The spray tip is worn out.
A worn-out spray tip is the most common cause of 'fingers' or 'tails' in an airless spray pattern. As the tip wears, the orifice loses its sharp edge and precise shape, leading to improper atomization, especially at the edges of the fan.
Why the other options are wrong
- A. A tip that is too large would typically lead to excessive material flow, runs, or sags, not 'fingers' or 'tails'.
- C. Fluid pressure that is too high would generally cause excessive atomization, fine mist, and potentially 'dry spray', not 'fingers' or 'tails'. Insufficient pressure is more likely to cause tails.
- D. Over-thinning would typically lead to a very fine spray, runs, and poor film build, not 'fingers' or 'tails'.
Airless Spray Pattern Defects (Fingers/Tails)
Unatomized streaks or heavier edges in an airless spray pattern, commonly caused by a worn spray tip or insufficient pressure.
- Indicates improper atomization of the coating.
- Most frequently caused by a worn spray tip.
- Can also be caused by insufficient fluid pressure.
Memory trick: Fingers and tails, the tip fails.