The essentials in 30 seconds
Hose off loose debris, then scrub with warm soapy water and a soft bristle brush, working the dirt out of the embossed grain, and rinse thoroughly: dirty water left to dry leaves a film. On composite decking, check which product you have: Trex says its high-performance lines can take soap and water or a gentle pressure wash (no more than 3,100 psi, fan tip, at least 8 in / 203 mm away), while its early-generation composites need a composite deck cleaner twice a year. Clean food and grease spills quickly. On wood decks, deck cleaners or brighteners remove mildew and dirt, but aggressive scrubbing with caustic cleaners or power washing can strip wood from the surface.
- Hard water spots on composite: white vinegar, then rinse.
- Tannin stains: a deck brightener with oxalic acid, used as its maker directs.
- Snow: plastic shovel only.
How to clean a composite deck
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01
Clear the debris
Sweep or hose off leaves, dirt and debris.
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02
Wet and wash
Warm soapy water with a soft bristle brush, scrubbing along each board to lift dirt from the embossing.
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03
Rinse thoroughly
Do not let dirty water dry on the boards, or it leaves a film.
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04
Pressure washer, if your boards allow it
Soap first, gentle brushing, then rinse each board with a fan tip, no closer than 8 in (203 mm) and within the maker's pressure limit.
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05
Treat stains
See the table below.
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06
Dry
If you rinse with hard water, dry with a cloth or a blower to avoid spots.
Composite deck stains and what to use
| Problem | What to do |
|---|---|
| Dirt and debris | Hose, then warm soapy water and a soft bristle brush |
| Food, oil and grease | Remove as soon as possible (Trex sets 7 days for its stain warranty); hose, soapy water, soft brush |
| Mould and mildew | Hose and warm soapy water with a soft brush, removing the pollen and dirt it feeds on |
| Hard water spots | White vinegar, then rinse with soft water or dry with a cloth or blower |
| Tannins from leaves | Remove debris, let the deck dry, apply a deck brightener (oxalic acid) as directed |
| Concrete, mortar or stucco dust | Protect the deck during building work; use a concrete dissolver following its instructions |
| Snow and ice | Plastic shovel; calcium chloride or rock salt to melt ice |
Which cleaner for composite decking
Trex splits its decking in two. For early-generation composites, it recommends cleaning twice a year with a composite deck cleaner. For its high-performance capped lines, soap and water or a gentle pressure wash is enough. Other brands have their own rules, so look up the care guide for your boards before using a pressure washer or a chemical deck cleaner. Rubber-backed mats can discolour or lighten composite boards, and most coloured chalks used during building are permanent.
How to clean a wood deck
The USDA Forest Products Laboratory explains that commercial deck cleaners, brighteners or restorers do not add colour: they remove mildew and dirt so the natural colour of the wood shows. If the colour has already leached out, the wood may look coloured when wet but silver when dry; those weathered fibres take stain well and should not be stripped off. Aggressive scrubbing with a caustic cleaner or power washing can remove wood from the surface, especially on soft woods such as western red cedar. For mildew, it describes household bleach diluted with 3 parts water plus some detergent (not a liquid detergent and never one with ammonia), rinsed off with water. If you are going to refinish, allow at least 2 warm, windy days for the wood to dry.
What not to do when cleaning a deck
- Letting dirty rinse water dry on the boards.
- Pressure washing beyond the maker's limit, or too close, on composite; power washing soft wood.
- Mixing bleach and ammonia, or using untested bleach or acid products on composite.
- Shovelling snow with anything but a plastic shovel on composite decking.
- Leaving leaves and pollen on the deck for long periods.
Deck cleaning: frequently asked questions
What is the best way to clean a composite deck?
Hose off debris, scrub with warm soapy water and a soft bristle brush, and rinse thoroughly. Some lines need a composite deck cleaner: check your product.
Can I pressure wash a composite deck?
Only if the manufacturer allows it. Trex allows up to 3,100 psi with a fan tip at least 8 inches away on its high-performance lines.
How do I remove mould from a deck?
On composite, warm soapy water and a soft brush. On wood, a deck cleaner, or bleach diluted with 3 parts water and some detergent without ammonia, then rinse.
How do I get hard water spots off composite decking?
White vinegar, then rinse with soft water or dry the boards with a cloth or blower.
Does power washing damage a wood deck?
It can. The USDA says power washing and caustic cleaners can strip wood from the surface, especially on cedar.
How long should a wood deck dry before staining?
At least 2 warm, windy days after cleaning, according to the USDA Forest Products Laboratory.
Sources
Manufacturer and government guidance, checked on 2 November 2026 (02/11/2026).
- Trex · Care guide: how to clean composite decking ↗Early-generation composites cleaned twice a year with a composite deck cleaner; high-performance lines with soap and water or gentle pressure washing; hose, warm soapy water and soft bristle brush; pressure washer no greater than 3,100 psi with fan tip no closer than 8 in (203 mm); rinse thoroughly to avoid film; concrete dust; hard water and white vinegar; chalk lines; tannins and oxalic acid brighteners; plastic shovel and salt; food spills within seven days for the stain warranty; mould and mildew; rubber mats; bleach or acid lighten the surface. Read in the browser.
- USDA Forest Service, Forest Products Laboratory · Finishes for wood decks (PDF, revised July 2013) ↗Deck cleaners, brighteners and restorers remove mildew and dirt; silver weathered fibres should not be removed; caustic cleaners or power washing can strip wood, especially western red cedar; bleach diluted with 3 parts water and detergent; no liquid detergent or ammonia; rinse; at least 2 warm, windy days to dry before finishing.
Soft, spongy or cracked boards?
Cleaning will not fix structural damage: stop using that area and have the deck inspected by a builder.