Finish TradesQuestion 219 of 700
Bare galvanized steel is to be painted. Which preparation gives the BEST long-term adhesion?
a.Apply an oil-based alkyd primer directly for a chemical bond
b.Leave the shiny zinc surface untouched and topcoat immediately
c.Sand only the visible rust spots and paint over the rest
d.Clean off oils, then use an etching or bonding primer formulated for galvanized metal
Explanation
Zinc coatings resist paint adhesion and react with oil-based (alkyd) primers to cause saponification and peeling. Cleaning the surface and using an etching or self-etching primer made for galvanizing gives durable adhesion. Direct alkyd primer fails, a slick untouched surface sheds paint, and spot-sanding rust ignores the zinc adhesion problem.
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