CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting contractor is preparing to paint new, unprimed exterior galvanized steel flashing. To ensure long-term adhesion and prevent premature peeling, what type of primer is specifically recommended for this substrate?
- AOil-based alkyd primer
- BWater-based latex PVA primer
- CDirect-to-metal (DTM) acrylic primer formulated for galvanized metal
- DZinsser B-I-N Shellac-Base Primer
Show answer & explanationAnswer & explanation
Correct answer: C. Direct-to-metal (DTM) acrylic primer formulated for galvanized metal
New galvanized metal has a passive zinc coating that can react with certain primers, leading to adhesion issues. A direct-to-metal (DTM) acrylic primer specifically formulated for galvanized metal is designed to adhere properly to this surface and prevent reactions.
Why the other options are wrong
- A. Oil-based alkyd primers can react with new galvanized metal, causing saponification and adhesion failure.
- B. Water-based latex PVA primers are typically for drywall and plaster, not for challenging metal surfaces like galvanized steel.
- D. Shellac-based primers are excellent stain blockers but not specifically formulated for the unique adhesion challenges of new galvanized metal.
Galvanized Metal Priming
The process of applying a specialized primer to galvanized steel to ensure adhesion and prevent reactions with the zinc coating.
- New galvanized metal requires specific primers.
- Avoid oil-based alkyds on new galvanized surfaces.
- Aged galvanized metal can be primed with more general DTM primers.
Memory trick: Galvanized needs a 'Direct' approach, not reacting with zinc.