A clean deck lasts longer. Dirt, pollen and leaves hold moisture against the boards, which feeds mould and mildew, and on wood it speeds up rot and greying. Most of the damage we see from cleaning comes from too much pressure or the wrong chemical, not from too little effort. This guide covers wood and composite separately, because they need different handling.
What you need
- Broom and a plastic putty knife for the gaps between boards
- Oxygen-based deck cleaner (sodium percarbonate) for wood, or the cleaner your composite maker recommends
- Stiff synthetic-bristle brush on a pole
- Garden hose with a spray nozzle
- Pressure washer with a 25 or 40 degree fan tip (optional)
- Plastic sheeting or a tarp for delicate plants
- Gloves and eye protection
- Oxalic acid wood brightener (optional, wood only)
When to clean
Once in spring after pollen season and once in fall before the leaves come down is enough for most decks. Pick a mild, overcast day. Cleaner that dries in hot sun streaks and stops working. If you plan to stain a wood deck, clean it first and allow it to dry fully before staining.
How to clean a wood deck
This covers pressure-treated, cedar and other wood decking.
- Clear and sweep. Move furniture, planters and the barbecue. Sweep, then clear debris from between the boards with a putty knife so water can drain.
- Protect plants. Soak surrounding plants with plain water and cover delicate ones.
- Wet the deck. Cleaner works better and more evenly on damp wood.
- Apply an oxygen cleaner. Mix to the label directions and apply with a pump sprayer or brush. Work in sections. Let it sit for the time on the label, usually 10 to 15 minutes, and keep it wet.
- Scrub. Use the synthetic brush along the grain. Pay attention to shaded spots, under planters and near the steps.
- Rinse. Rinse thoroughly with a hose, or a pressure washer set low, around 500 to 1,200 psi with a wide fan tip. Keep the tip about 30 cm (12 inches) away and move with the grain. Softwoods like cedar need the lower end of that range.
- Brighten (optional). An oxalic acid brightener restores colour and neutralises the cleaner. It is especially useful on cedar and before staining.
- Dry. Let the deck dry at least 48 hours before staining. Sprinkle a little water on a board. If it soaks in quickly, the wood is ready for stain. If it beads, wait or check whether old sealer is still on the surface.
Why not chlorine bleach?
Chlorine bleach kills surface mould but does not clean well, damages wood fibres, can leave boards blotchy and harms plants and grass. Oxygen cleaners break down dirt and mildew without those problems.
Pressure washing wood: where it goes wrong
Too much pressure, a narrow tip or holding the wand too close cuts into soft wood, lifting fibres and leaving marks that look like tiger stripes. That furred surface needs sanding before it will take stain evenly. If you are not confident, a hose and a brush get most decks clean.
How to clean a composite deck
- Check your warranty first. Find the care guide for your decking line. Rules differ between brands and between older and newer lines.
- Sweep and clear gaps. Debris in the gaps traps water and feeds mould.
- Wash with soap and water. Warm soapy water or the recommended composite cleaner and a soft-bristle brush handles routine dirt.
- Rinse. A garden hose is usually enough. If you use a pressure washer, stay inside the manufacturer's limits.
- Dry. Let it dry and check for any remaining spots.
| Brand | Pressure washer guidance |
|---|---|
| TimberTech | Fan tip, 1,500 psi maximum, per the TimberTech care and cleaning guide |
| Trex, newer lines | Fan tip, under 3,100 psi, held at least 20 cm (8 inches) from the surface, per the Trex care and cleaning guide |
| Trex, some older lines | No pressure washing. Check your product line in the Trex guide |
| Other brands | Follow your manufacturer's care guide. If in doubt, use a hose and a brush |
Never sand a composite deck, and do not use a wire brush or metal scraper. Both damage the protective cap.
Stains and problem spots
| Problem | Wood deck | Composite deck |
|---|---|---|
| Green or black mould and mildew | Oxygen cleaner, scrub, rinse | Composite cleaner or soapy water, soft brush. Deep spots may need a cleaner made for mould on composite |
| Grease from the barbecue | Degreasing deck cleaner quickly, before it soaks in | Warm soapy water as soon as possible |
| Rust marks | Oxalic acid brightener | Cleaner approved by the manufacturer for rust |
| Grey, weathered boards | Oxygen cleaner, then brightener | Normal weathering, cannot be refinished |
| Leaf tannin stains | Oxygen cleaner and brightener | Usually fades with cleaning and sun |
| Ice melt residue | Rinse in spring | Rinse in spring, follow the maker's list of safe ice melts |
After cleaning: stain or seal?
Wood decks need a stain or sealer to stay protected. Cedar usually needs it every 2 to 3 years, and pressure-treated decks in full sun often need attention more often. Apply only to clean, dry wood, in the temperature range on the product label, and avoid rain for at least a day. If the old finish is peeling, it needs to be stripped or sanded first, or the new coat will peel with it.
Composite decks do not need staining or sealing.
What a pro costs
Professional cleaning of a typical 200 to 300 sqft deck usually runs about $250 to $600. Cleaning, sanding and re-staining is typically $3 to $6 per square foot. If boards are loose, cupped or soft, have them checked before the stain goes on. Our deck warping, splintering and squeaking guide explains what to look for.
Winter care
- Clear snow with a plastic shovel, pushing along the boards, not across them.
- Do not chip at ice with metal tools.
- On composite, use only ice melt products the manufacturer allows, and rinse residue off in spring.
- Keep gaps clear of leaves before the first snow so meltwater can drain.
Frequently asked questions
What is the best way to clean a wood deck?
Sweep it, wet it, apply an oxygen-based deck cleaner, scrub with a synthetic brush along the grain, and rinse with a hose or a pressure washer on low pressure with a wide fan tip.
What psi should I use to pressure wash a deck?
For wood, around 500 to 1,200 psi with a 25 or 40 degree fan tip held about 30 cm away, lower for cedar. For composite, follow the maker: TimberTech says 1,500 psi maximum, and Trex allows under 3,100 psi on newer lines but no pressure washing on some older ones.
Can I use bleach to clean my deck?
Chlorine bleach is not recommended. It damages wood fibres, can leave blotches and harms plants. Oxygen-based cleaners work better and are gentler.
How do I clean a composite deck?
Sweep it, wash with warm soapy water or a cleaner your manufacturer recommends, scrub with a soft brush and rinse with a hose. Check your warranty before using a pressure washer.
How often should I clean my deck?
Twice a year for most decks, in spring after pollen season and in fall before the leaves drop. Shaded or damp decks may need more attention.
How long after cleaning can I stain my deck?
Usually at least 48 hours of dry weather. Sprinkle water on the boards. If it soaks in quickly, the wood is ready.
How do I get mould off a deck?
On wood, use an oxygen-based cleaner and a stiff synthetic brush. On composite, use soapy water or a cleaner approved by the manufacturer and a soft brush. Clear the gaps so the deck can dry out.
Can I make my own deck cleaner?
A simple option is oxygen bleach powder (sodium percarbonate) mixed with warm water according to the package. For composite, mild dish soap and warm water handles routine dirt.
- Our deck building service
- Why is my deck warping, splintering or squeaky?
- Pressure-treated vs cedar vs composite decking
- Deck cost in Ontario
- How to clean an interlocking patio
Found loose or soft boards? See 2026 deck repair costs for boards, stairs, railings and framing.