Honestly, I’d start with this rule of thumb: seal a wooden park bench once a year if it lives outside in the open. If the bench sits under a pavilion, deep shade, or only gets mild weather, every two to three years is usually enough. In harsh climates—heavy snow, coastal salt air, strong UV—I’d lean toward every 6–12 months with a penetrating sealer, or at least do a quick water-bead test each spring and fall.
The exact answer depends on three things: the wood, the finish, and the exposure. Dense hardwoods like teak or ipe hold up longer, but most park benches are built from pine, cedar, oak, or acacia, and those need more consistent protection. A penetrating oil-based sealer soaks into the grain and generally lasts 12–18 months outdoors; a film-forming spar varnish or polyurethane can go 2–3 years but takes more prep when it starts to peel.
I use a simple test before resealing: splash a little water on the bench. If the water beads up, the sealer is still working. If it soaks in and darkens the wood within a few seconds, the bench is thirsty and ready for a fresh coat. Also look for fading, small cracks, rough grain, or spots that stay damp after rain—those are all signs it’s time.
When you do seal it, don’t just slap sealer over dirt. Clean the bench with mild soap and water or a wood cleaner, rinse well, and let it dry for at least 24 to 48 hours. Lightly sand any rough or gray areas with 120–150 grit sandpaper, wipe off the dust, then apply the sealer in thin, even coats with a brush, foam brush, or rag. With oil-based products, wipe away excess after 20–30 minutes so the surface doesn’t get sticky. Two thin coats usually beat one thick coat.
One mistake I see often is over-sealing. If a film finish builds up too much, it can trap moisture, turn milky, and peel. That’s why I prefer a penetrating sealer for most park benches—it’s easier to maintain and lets the wood breathe.
So my honest recommendation: plan on once a year for a typical outdoor wooden park bench. If you use a high-quality penetrating sealer and the bench doesn’t get hammered by weather, you can likely stretch it to every 18–24 months. Check it each spring, and let the water test make the final call.