What Finish Protects a Steel Gate From Salt Air

A snow-covered alleyway in Hartford, CT with a brick building and wrought iron gate.

Within a mile of the marine layer in Carlsbad, CA, the finish decides how long a steel gate lasts more than the grade of steel does. The running record steel gates carlsbad three word wednesday holds shows rust starting at welds, tube ends and fastener holes long before flat surfaces give out. Those are the places a finish system has to be built around.

Why salt air is harder than rain

Black and white image highlighting complex shadow patterns on an ornate iron gate.

Salt from sea spray settles on the frame and stays there. It attracts and holds moisture, so corrosion keeps running long after plain dew would have dried off. Gates near agua hedionda lagoon or batiquitos lagoon see this on a regular cycle. A gate on the east side of interstate 5 gets less of it, but it is not exempt.

Hot dip galvanizing first

Stone gate adorned with autumn decorations, framed by fall foliage, leading to a traditional home.

Hot dip galvanizing dips the finished steel in molten zinc. The zinc forms alloy layers bonded to the steel, not a film sitting on top. Zinc is sacrificial, so at a small scratch the surrounding zinc corrodes first and helps protect the exposed steel. Galvanized tubing, picket and frame are coated inside and out, which a brushed or sprayed paint cannot match.

Weld before the zinc goes on

Galvanizing after welding is preferred. Welding burns off zinc, and any weld made after galvanizing needs a zinc rich repair coating. On a swing gate hinge post, a field weld is the spot to inspect first at every service visit. Plan the cutting and fitting so the shop does the welding and the zinc goes on last.

Powder coat over the zinc

A duplex system, galvanizing followed by powder coat or paint, generally lasts longer than either layer alone because each protects the other. Powder coat alone does not make steel rustproof. Over galvanized steel the surface needs correct preparation, and gases trapped in the zinc can cause pinholes or bubbles if the part is not degassed before coating. Thicker paint does not always mean longer life. Clean prep and sound adhesion count for more than mils.

Drain holes and mixed metals

Hollow tube members should have drain and vent holes so water and salt mist that get inside can escape. A sealed tube can hold a wet salt pocket for years. Hardware needs the same attention. Mixing dissimilar metals, such as certain fasteners touching zinc coated steel, can speed corrosion of the less noble metal in wet salty conditions. Hinges, operator brackets and gate opener mounts should be matched to the coating, and stainless parts still need rinsing, because stainless can stain near the ocean.