That's an excellent and very practical question for anyone living near or designing spaces for coastal areas. The short answer is: it depends entirely on the metal and the protective finish. Not all metal benches are created equal for this harsh environment.
Salt air is highly corrosive because it contains chloride ions that accelerate rust and oxidation, especially on ferrous metals (those containing iron). Here’s how different materials hold up:
Powder Coated Steel: This is a common and robust option. The powder coating is a dry electrostatically applied finish that is then heat-cured, creating a much thicker, more uniform, and adhesive layer than traditional paint. A high-quality powder coat acts as a formidable barrier against salt and moisture. Look for benches with a "marine-grade" powder coat specification for the best defense. Minor chips should be touched up promptly.
Aluminum: Specifically, marine-grade aluminum (like the 6000 series) is a top-tier choice for coastal zones. Aluminum naturally forms a protective oxide layer, and when combined with a powder coat or anodized finish, it becomes exceptionally resistant to salt corrosion. It's also lightweight and strong. You'll often find this in high-end coastal furniture.
Stainless Steel: Not all stainless is equal for coastal use. You need Grade 316 stainless steel, often called "marine-grade stainless." It contains molybdenum, which provides superior resistance to chloride-induced pitting and crevice corrosion. It's more expensive but can last for decades with minimal care, often developing a soft patina.
Cast Aluminum: Similar to marine-grade aluminum, cast aluminum benches with a proper powder-coated finish perform very well. The casting allows for intricate, durable designs.
Maintenance is Key: Even the best materials benefit from simple care. Rinse your benches periodically with fresh water to remove salt residue. Inspect powder coatings annually for chips. Avoid harsh abrasive cleaners that can damage protective finishes.
In summary, for long-term performance in coastal areas, invest in benches made from marine-grade aluminum with powder coat, or Grade 316 stainless steel. Avoid plain, painted, or low-grade steel, as they will succumb to rust quickly. The right choice will provide years of beautiful, durable seating despite the challenging salt-air conditions.