Most advice about deck maintenance is written for places with real seasons — hot dry summers, sun that bleaches wood, rain that stops for months at a time. That advice doesn't map well onto San Francisco. Here, the thing quietly wrecking your deck isn't UV exposure. It's fog.
Why fog is harder on wood than sun
Sun damage is a slow, visible process — graying, fading, the occasional split board. Fog damage is slower to notice and worse underneath. Every foggy morning, your deck boards absorb a thin layer of moisture. Every afternoon, if the sun comes out, that moisture evaporates. That cycle — wet, dry, wet, dry — happens far more often in the Sunset, Richmond, or anywhere within a few blocks of Ocean Beach than it does in sunnier pockets of the city. Repeated swelling and shrinking is what breaks down a sealant coat and eventually opens up the wood grain to rot.
A deck that looks fine from a few feet away can already have a compromised sealant layer. The way to check is simple: pour a small amount of water on a board in a shaded area. If it beads up, you're fine. If it soaks in within a minute or two, the seal is gone and the wood is exposed.
A realistic resealing timeline
These are starting points, not rules — actual exposure, wood type, and how the deck was built all shift the number. But as a baseline for Bay Area conditions:
- Redwood or cedar, fog-belt exposure (Sunset, Richmond, Outer Parkside, coastal Pacifica): every 1–2 years.
- Redwood or cedar, sunnier/inland exposure (Noe Valley, Bernal Heights, inland Peninsula): every 2–3 years.
- Pressure-treated pine, any exposure: every 1–2 years — pine is more porous and takes on moisture faster than redwood or cedar.
- Composite decking: doesn't need sealing, but fittings, railings, and any real-wood trim around it still do.
What a proper resealing actually involves
The finish coat gets all the attention, but it's the least important part of the job. Most deck failures we see trace back to skipped prep, not a bad product:
- Wash and strip first. A pressure wash (careful, low-pressure setting on softwood) removes dirt, mildew, and the failing remnants of the old coat.
- Let it dry fully. Sealing over damp wood traps moisture underneath the new coat — often worse than not sealing at all. In fog season, that can mean waiting several extra days for a clear stretch.
- Sand rough or splintering boards before the new coat goes on, not after.
- Two thin coats beat one thick one. A heavy single coat looks fine on day one and peels within a season.
Signs it's time now, not next spring
- Water soaks in instead of beading on shaded boards
- Gray, silvery patches spreading across the deck surface
- Splinters or rough texture underfoot
- Dark or soft spots near the ground or against the house — early rot, worth a same-week look
If you're not sure which category your deck falls into, that's a fair reason to have someone look at it in person rather than guess from a blog post. We check the framing while we're up there anyway — a resealing visit is also when we catch loose railings or joists before they become a bigger repair.