When protecting wooden outdoor benches in rainy climates, your finish choice becomes critical for longevity. For maximum protection, I recommend marine-grade spar varnish as your top contender. This specialized finish contains UV blockers and remains flexible to accommodate wood's natural expansion and contraction during wet-dry cycles. Apply three to five thin coats, sanding lightly between layers for optimal adhesion.
For those preferring a natural look, high-quality teak oil provides excellent water resistance while enhancing the wood's grain. It requires more frequent reapplication—typically annually—but offers easier maintenance without peeling. Modern outdoor-rated polyurethane represents another solid option, with advanced formulations specifically designed for moisture resistance.
Always begin with properly prepared wood: clean, dry, and sanded surfaces ensure finish adhesion. Consider adding a water-repellent preservative beneath your topcoat for extra protection against mold and mildew. Regardless of your chosen product, regular inspection and maintenance will significantly extend your bench's life in challenging wet conditions. Reapply finish at the first signs of water beading failure to prevent moisture penetration that leads to rot and deterioration.