Yes—in most cases, an urban bench should be treated or sealed before it is installed near the coast. The combination of salt spray, high humidity, strong sun, and wind-driven sand is much harder on outdoor furniture than a typical inland park setting.
If the bench is wood, treatment is basically non-negotiable. Untreated wood near the coast will absorb moisture, swell, dry out, and crack. Salt crystals can get into the grain and accelerate fiber breakdown. A penetrating wood preservative or marine-grade sealant should be applied to all sides, including end grain and any cuts or drilled holes. For hardwoods like teak or ipe, a sealer still helps preserve the natural color and reduces surface checking, even though the wood itself is naturally durable.
For metal benches, the main risk is corrosion. Powder-coated steel or galvanized steel is common for urban furniture, but if the coating is scratched during transport or installation, salty air will find it quickly. Before installation, touch up any chips and consider applying a clear rust-inhibiting coating or automotive-grade wax on vulnerable areas. Stainless steel benches are more resistant, but even some grades of stainless can develop tea staining in coastal conditions. A protective coating or regular cleaning schedule can prevent that.
Composite and plastic benches need less sealing, but they still benefit from UV protection. Salt residue can build up on the surface, so a light protective coating or simply planning for regular rinsing is a good idea. Check the manufacturer’s recommendations because some recycled plastic lumber is completely maintenance-free.
Installation details also matter. Use stainless or galvanized fasteners, and avoid letting untreated wood or raw steel edges sit directly on wet ground or in standing water. Seal any end grain that will face upward or absorb rain. If you pre-treat before installation, you can cover every side while the bench is easy to access, which is much harder after it is anchored in place.
The short answer: yes, treat or seal it. The exact product depends on the material, but coastal exposure shortens the life of any bench that is installed without protection.