How to wash the siding and deck, and reseal the deck
To clean and seal a deck, wash it yearly with a wide fan tip at moderate pressure, moving with the grain. If water soaks in rather than beading, let the wood dry and reseal it. Sealer life ranges from one year to several, depending on the product. Wash siding gently, following its maker's care guide.
How often to seal a deck and wash siding
| Job | How often |
|---|---|
| Wash the deck | At least once a year, to remove algae and mildew |
| Water test the deck | Each year, after washing |
| Reseal the deck | When water stops beading. Some products suggest yearly recoats, and some brands claim 5 to 6 years. |
| Wash the siding | When dirt or mildew shows |
A sealer's lifespan depends on sun and weather. UV-blocking ingredients can break down within months in hot, sunny climates, so treat brand claims as a best case. Bob Vila's guide suggests a simple water-based coat each year before summer for sun protection.
Deck sealer, cleaner and other supplies
- Deck cleaner and a stiff brush. Viance, a maker of wood treatments, prefers sodium percarbonate or oxalic acid cleaners to bleach.
- A pressure washer with white or green fan tips, or a garden hose and scrub brush
- Sealer or stain, plus a brush, roller or pad
- Eye protection and closed shoes
Sealers come in two main types. Water-based products clean up with soap and water, and oil-based ones are more forgiving on rough wood. Pick the type for your deck, then follow its label for temperature and recoat time.
| Sealer | Dry to touch | Second coat | Full cure |
|---|---|---|---|
| Water-based | About 1 to 3 hours | A few hours later | Up to 24 hours |
| Oil-based | About 4 to 12 hours | After about 24 hours | Up to 72 hours |
Bob Vila gives those water-based times for about 60 to 90°F and humidity of 50% or lower. Oil-based sealer bubbles more easily on a deck that isn't fully dry.
How to clean and seal a deck, and wash the siding
- Check the structure first
Walk the deck, shake the railings and look underneath. Fix anything loose or rotten before you clean.
- Choose a dry stretch of weather
Look for mild days with no rain expected through drying and sealing. Move furniture and planters off the deck.
- Wash the siding gently
Use cleaner and a soft brush or low pressure. Spray down the wall, not up under the laps, and keep water away from vents and outlets.
- Practice before you touch the deck
Try the washer on the driveway or an old pallet. Use a white or green fan tip and avoid red and yellow tips, which can gouge wood.
- Wash with the grain
Keep the tip at least 8 inches from the wood and moving at all times. Hold it more than 12 inches away when you change direction, to avoid a stop mark.
- Let the wood dry
Wait until it's fully dry. Shade and humidity add time, and sealer applied to damp wood can fail.
- Test, then seal
Sprinkle water on the boards. If it soaks in, apply a thin, even coat along the boards, following the label.
When not to pressure wash a deck
- Boards that feel soft or crumble when you press with a screwdriver. That's likely rot.
- Loose railings, wobbly posts or gaps where the deck meets the house. Stay off it and call a licensed contractor or structural pro.
- Peeling paint on a house built before 1978. It may be lead paint, and EPA warns that disturbing it creates dangerous dust. Don't pressure wash it. Get it checked first.
- Paint or stain stripped by your wash. Decks.com warns of that above about 2,500 PSI, and of permanent wood damage above 3,000 PSI.
How to clean and seal a deck yourself, or hire a pro
A small, sound deck is a fair DIY job. Sources disagree on pressure: Viance says no more than 800 PSI, while Decks.com starts around 1,800. Start low and go up only if the dirt stays put. Hire a pro for high second-story siding, since working from a ladder with a pressure washer is risky. Do the same for any older house with failing paint. Before you wash siding, read the maker's care guide, because the rules differ between vinyl, wood and fiber cement.
Deck sealer and pressure washing questions
How often should you seal a wood deck?
It depends on the product and your climate. Some sealers suggest yearly recoats, and some brands claim 5 to 6 years. Run a water test each year and reseal when water stops beading.
What PSI should I use on a wood deck?
Viance recommends no more than 800 PSI as a cautious limit, though experts disagree. Start low with a fan tip and only increase pressure if you need it.
Can I pressure wash old painted siding?
Be careful with pre-1978 homes, where paint may contain lead. If the paint is peeling, get advice from a certified lead inspector or a lead-safe certified contractor before you wash.
Sources: treatedwood.com, decks.com, Bob Vila, EPA
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.