316 Stainless vs Hot-Dipped Galvanized — Coastal NC Dock Hardware

Hot-dipped galvanized fasteners rely on a zinc coating to protect the underlying steel. In coastal NC salt spray and humidity, that zinc layer is consumed in 3–5 years on exposed connections and 5–7 years even on shaded ones. Once the zinc is gone, the steel rusts at full speed.

The visible symptoms: orange staining on decking around fasteners, "weeping" rust streaks down pilings, and eventual loss of fastener head — meaning the joint has lost its mechanical connection.

316 stainless steel contains molybdenum (2–3%), which gives it specific resistance to chloride pitting — the exact corrosion mode in salt water. In coastal NC tests, 316 fasteners installed in 1990s docks show no measurable corrosion after 30+ years.

Do not confuse with 304 stainless. 304 lacks molybdenum and will pit in salt spray within 8–12 years. For marine use, only specify 316.

• 316 stainless: Every deck screw, lag bolt, through-bolt, hinge, cleat fastener, and float-drum connection in the splash zone or below.
• Hot-dipped galvanized: Acceptable for internal framing connections (joist hangers, hurricane straps) that are completely shielded from direct rain and spray.
• Never use: Bright zinc-plated or "marine grade" non-stainless hardware. These last 18 months at best.