Coastal air carries chlorides that attack steel. The closer you are to the sea and the more wind‑driven spray you get, the tougher the environment. Here’s a practical way to choose between galvanized steel and stainless, and when to step up to higher alloys.
Quick decision guide
- Interior or sheltered, >10 km from coast: Galvanized (G90/Z275) is usually fine. Paint if you want longer cosmetic life.
- General exterior, ~1–10 km from coast: Galvanized G185/Z565 or Al‑Zn (AZ150) with good paint; or stainless 304 for hardware and fasteners.
- Near coast/spray, <1 km or on the shore: Prefer stainless 316 (or duplex 2205) for critical items; use high‑class galvanizing with robust paint for large panels and protect cut edges.
- Splash/immersion: Stainless 316/2205; avoid relying on galvanizing alone in constant chloride wetting.
What really fails in coastal sites
- Cut edges: Galvanized sheets rust first at cut edges; seal with zinc‑rich paint and good topcoats.
- Fasteners: Mixed metals (zinc sheet + carbon‑steel screws) corrode fast. Use stainless or coated compatible fasteners with EPDM washers.
- Crevices and deposits: Salt collects in joints. Design open details that can rinse clean.
Material notes
- Galvanized: Higher coating mass lasts longer. Paint systems with PVDF or high‑build primers help in UV and salt.
- Al‑Zn (Galvalume): Good overall corrosion resistance; still protect edges and fasteners.
- Stainless 304 vs 316: 316’s molybdenum resists chloride pitting better; choose it for coast‑facing rails, fixings and wash‑down areas.
Spec snippets
- Cladding/panels (coastal): AZ150 + PVDF topcoat; cut‑edge seal; stainless fasteners.
- Handrails/hardware: 316L stainless; brushed finish; avoid carbon‑steel tooling cross‑contamination; passivated after fab.
- Frames/supports: Hot‑dip galvanized with high‑build paint system; seal welds and edges.
Tell us distance from shore, exposure (open coast or sheltered) and maintenance expectations. We’ll suggest a durable material/finish set and the right fasteners to match.