NASCLA Accredited Commercial General ContractorFinishesHard
A painting contractor is preparing to apply a finish coat to an exterior galvanized steel door frame. The frame was recently installed and has visible spangle. To ensure proper adhesion and long-term durability of the paint system, what type of primer is MOST appropriate for this specific substrate?
- AOil-based stain-blocking primer
- BZinc-rich epoxy primer
- CWater-based acrylic latex primer
- DAlkyd-based bonding primer
Show answer & explanationAnswer & explanation
Correct answer: B. Zinc-rich epoxy primer
Galvanized steel requires a primer that can adhere well to the zinc coating and provide corrosion protection. A zinc-rich epoxy primer is specifically formulated for this purpose, offering excellent adhesion and galvanic protection to prevent 'white rust' and ensure paint longevity.
Why the other options are wrong
- A. Oil-based stain-blocking primers are for preventing stains from bleeding through paint, not for priming galvanized metal.
- C. While some acrylic latex primers are suitable, a dedicated zinc-rich epoxy primer offers superior adhesion and corrosion protection for new galvanized steel.
- D. Alkyd primers can react with the zinc in galvanized steel, leading to poor adhesion and premature paint failure (saponification).
Zinc-Rich Epoxy Primer
A two-component primer containing a high concentration of zinc dust that provides galvanic and barrier corrosion protection, and excellent adhesion to galvanized steel and other ferrous metals.
- Chemically bonds well with zinc in galvanized coatings.
- Offers sacrificial (galvanic) protection against rust.
- Essential for painting new or weathered galvanized steel.
Memory trick: Galvanized steel with spangle? Zinc-rich primer is the right angle.