CSLB C-33 Painting & DecoratingCoating ApplicationMedium
A painting contractor is applying a high-build elastomeric coating to a stucco exterior using an airless spray rig. After several passes, the contractor observes that the spray pattern has 'fingers' or 'tails' at the edges, and the coverage appears uneven. Which of the following is the MOST likely cause of this issue?
- AThe contractor is spraying too close to the substrate.
- BThe spray tip is worn out and needs to be replaced.
- CThe air pressure setting on the compressor is too high.
- DThe coating material is too thin for the spray tip being used.
Show answer & explanationAnswer & explanation
Correct answer: B. The spray tip is worn out and needs to be replaced.
Fingers or tails in an airless spray pattern are a classic indication that the spray tip is worn. A worn tip loses its sharp, clean edge, causing the paint to flow unevenly through the orifice and resulting in an inconsistent spray pattern with heavy edges.
Why the other options are wrong
- A. Spraying too close usually results in a heavy, wet coat and potential runs or sags, not 'fingers' in the pattern.
- C. Airless sprayers do not use air pressure to atomize paint; they use hydraulic pressure. If speaking of fluid pressure, too high pressure might cause excessive atomization or overspray, but not typically 'fingers'.
- D. If the material were too thin, it would typically atomize too finely or run, not cause 'fingers' at the edges.
Airless Spray Tip Wear
Airless spray tips wear out over time, causing a loss of spray pattern integrity, often manifesting as 'fingers' or 'tails' at the edges of the fan.
- Tip wear increases the orifice size and changes the fan angle.
- Worn tips lead to uneven coverage and increased material consumption.
- Regular inspection and replacement of tips are crucial for quality application.
Memory trick: A tired tip makes the paint flow like fingers through a sieve.