Great question—because in a rainy city, a finish isn’t just decoration. It’s the barrier between the bench and constant moisture, temperature swings, UV exposure, and street grime.
If I had to choose one most durable finish for the wood parts of a street bench, it would not be a single can from the hardware store. It would be a system: a two-part epoxy wood sealer followed by three coats of marine-grade polyurethane with UV inhibitors. Marine polyurethane is harder and more water-resistant than standard spar varnish, and it handles the wet-dry cycling that kills most outdoor finishes. Spar varnish is more flexible and UV-friendly, but it stays softer, so on a public bench it can get scratched and worn more quickly. The epoxy sealer underneath does the real waterproofing, especially on end grain and joints where rain tends to sit.
For the metal frame or metal slats, powder coating is the most durable finish you can get for a rainy city. It is electrostatically applied and baked into a tough, fused layer that resists chipping, scratching, and corrosion far better than wet paint. Look for an architectural-grade powder coat—polyester or super-durable polyester—not a cheap single-coat job. If the bench is aluminum, powder coating gives it a long life. If it’s steel, make sure it is pre-treated properly, ideally galvanized or phosphate-washed first, otherwise rust can crawl underneath the coating from the inside out.
One important warning: on solid wood benches, thick film finishes like polyurethane can eventually trap moisture if the coating gets cracked or scratched. That’s why the epoxy sealer and proper end-grain sealing matter so much. If you want the absolute lowest-maintenance route in a rainy city, skip the paint film on wood and use a naturally rot-resistant hardwood like teak, ipe, or thermally modified ash, then maintain it with a penetrating oil. But per application, a penetrating oil is less durable than a well-applied marine polyurethane system—it just fails more gracefully.
So my practical ranking for a rainy city street bench:
- Wood slats: epoxy sealer + marine-grade polyurethane topcoat.
- Metal frames: architectural polyester powder coat over galvanized or properly prepped steel/aluminum.
- Hardware: stainless steel bolts, because rusty hardware ruins even the best finish.
- Avoid: standard exterior paint, cheap varnish, bare carbon steel, and any finish applied without sealing end grain.
If you can only do one thing and the bench is already built, choose a marine-grade polyurethane for exposed wood and touch up any powder-coated metal with a rust-inhibiting paint. But if you’re specifying a new street bench for a rainy city, choose powder-coated metal and either composite/recycled plastic or well-sealed hardwood—that combination will outlast any single “miracle” coating.