CSLB C-33 Painting & DecoratingSurface PreparationHard
A painting contractor is preparing a metal railing for repainting. The existing paint is sound, but there are several small areas where rust has started to form due to minor scratches and chips. What is the most effective approach to treat these localized rust spots before applying a new topcoat?
- ASand the rust down to bare metal, apply a rust-inhibitive primer, then topcoat.
- BApply a rust converter directly over the rust, then prime with a universal primer.
- CWire brush the rust loose and apply a direct-to-metal (DTM) paint.
- DClean the rust with a degreaser and paint over it with an oil-based enamel.
Show answer & explanationAnswer & explanation
Correct answer: A. Sand the rust down to bare metal, apply a rust-inhibitive primer, then topcoat.
For localized rust, physically removing the rust down to bare, clean metal is crucial. A rust-inhibitive primer then provides an anti-corrosive barrier and ensures optimal adhesion for the new topcoat, preventing future rust formation.
Why the other options are wrong
- B. Rust converters stabilize rust but do not remove it, and a universal primer might not offer sufficient rust-inhibitive properties.
- C. Wire brushing may not remove all rust, and DTM paints are often better for new metal or light rust, not established spots.
- D. Degreasing cleans but does not treat rust, and painting directly over rust will lead to continued corrosion and paint failure.
Metal Rust Remediation
The process of removing existing rust from metal surfaces and applying a protective coating to prevent future corrosion.
- Mechanical removal (sanding/grinding) is often required.
- Rust-inhibitive primers are essential.
- Ensures longevity of paint system on metal.
Memory trick: To stop rust's spread, sand to bare, then 'prime' ahead.