CSLB C-33 Painting & DecoratingSurface PreparationHard
A painting contractor is preparing an exterior, previously painted metal door that exhibits minor surface rust spots and some areas of intact but dulled paint. What is the most effective preparation sequence for this door before applying a new topcoat?
- AWire brush rust spots, clean entire door, apply rust-inhibitive primer to entire door, then paint.
- BWash door, then apply rust converter to rust spots, then prime entire door, then paint.
- CScrape off all old paint, then sand entire door, then apply DTM primer, then paint.
- DLightly sand all surfaces, then prime over rust spots, then paint.
Show answer & explanationAnswer & explanation
Correct answer: A. Wire brush rust spots, clean entire door, apply rust-inhibitive primer to entire door, then paint.
The most effective sequence for previously painted metal with minor rust is to first mechanically remove loose rust, thoroughly clean the entire surface, then apply a rust-inhibitive primer to ensure protection and adhesion, and finally apply the topcoat. Rust converters only stabilize rust but don't remove it, and sanding alone isn't always sufficient for rust removal or adhesion on metal.
Why the other options are wrong
- B. Rust converters stabilize rust but don't remove it, and a dedicated rust-inhibitive primer is generally preferred for active rust protection.
- C. Scraping all old paint is often unnecessary if adhesion is good, and a DTM primer is specific, but rust inhibition is the key here.
- D. Light sanding might not fully address rust, and spot priming might lead to uneven adhesion or protection.
Metal Rust Remediation
The process of treating and preventing rust on metal surfaces before painting, crucial for paint longevity and adhesion.
- Mechanical removal of loose rust is primary.
- Rust-inhibitive primers are essential.
- Cleanliness and proper drying are critical.
Memory trick: Rust out, Clean up, Prime all, Paint on.