Sealing Exterior Wood: Siding, Decks and Fences

The sun breaks down wood surface fibers (graying); water then moves through those open fibers, causing swelling, checking and rot. Sealing is a maintenance cycle, not a one-time event — plan on recoating decks every 1–3 years, siding 5–8, fences 2–4 depending on product and exposure.

Match product to wood

• Clear sealers: show grain, weakest UV protection — fastest recoat cycle.
• Toned/semi-transparent stains: pigment absorbs UV; the sweet spot for most decks.
• Solid stains: paint-like hiding, longest cycle, but peel instead of fade when they fail.
• Pressure-treated lumber: still needs sealing — treatment protects against rot and insects, not water and sun. Wait until it’s dry (water beads test) before sealing.

Prep decides everything

1. Clean — Deck cleaner or oxygenated bleach, scrub, rinse. A pressure washer can help at wide fan, low pressure — up close it scars softwood.
2. Strip old failing finish — Peeling solid stain comes off with stripper; semi-transparent often just needs cleaner.
3. Sand and brighten — 60–80 grit where fuzzy; wood brightener restores pH after cleaners so stain tone stays true.
4. Dry 2–3 days — Sealer on damp wood traps moisture — the moisture-bead test tells you when it’s ready.

Apply thin — two thin coats beat one pooled coat; pooled sealer stays tacky and fails early. Back-brush board by board. End grain of cut boards drinks twice: seal cuts as you go.