Hot-Dip Galvanizing or Paint: Choosing Your Corrosion System

Where should the anti-corrosion budget go? It depends on design life and environment — not on price.

Corrosion protection is a function of environment class × design life — both matter:

Hot-dip galvanizing: with 85μm+ zinc, maintenance-free for 25+ years. Ideal for purlins, girts and rails, and for primary structures in coastal or chemical environments. Limits: member size is bounded by the zinc bath, and heat distortion must be controlled.

Paint systems: typically zinc-rich epoxy primer + epoxy micaceous intermediate + polyurethane topcoat, total dry film 120–280μm per environment class C2–C5. No size limit, any color — but requires scheduled repainting.

The best value is often a combination: paint on primary steel, galvanizing on secondary members, budgeted where it matters. Whichever system, state it in the contract with film thickness — vague wording like "ordinary anti-rust paint" is a dispute waiting to happen.