Cleaning Composite Decking: Best Methods and Tips

Composite decking is marketed as low-maintenance, and it is — but low-maintenance is not no-maintenance. Dirt, pollen, mold, grease, and mildew still build up on the surface, and how you handle them makes the difference between a deck that looks new for 25 years and one that stains and streaks. Cleaning composite decking correctly means using the right products, the right technique, and knowing what to avoid so you don’t void your warranty or damage the boards. This guide covers routine care and every common stain.

Part of our Decks & Outdoor guide — explore the full guide →

Composite Is Not Wood — Clean It Differently

Composite boards are a blend of wood fibers and recycled plastic, often with a protective polymer cap on newer capped composite products. That cap resists moisture and stains, but it can still be scratched or dulled by harsh tools and chemicals. Unlike wood, composite never needs sanding, staining, or sealing. It just needs the right cleaning routine to remove the film of grime that dulls its color.

Your Basic Cleaning Kit

For routine cleaning you only need a few things:

• A bucket of warm water and mild dish soap
• A soft-bristle brush — never a stiff wire or hard nylon brush
• A garden hose with a spray nozzle
• A dedicated composite deck cleaner for tougher jobs

That simple kit handles the vast majority of dirt and pollen. Save specialty cleaners for stains that soap won’t lift.

The Routine Soap-and-Water Method

At least twice a year — spring and fall — give the deck a full wash:

• Sweep off leaves and loose debris first.
• Rinse the deck with the hose to loosen surface dirt.
• Mix warm water and dish soap, and work one section at a time so the soap doesn’t dry.
• Scrub gently along the grain with the soft brush.
• Rinse thoroughly before the soapy water dries, which prevents streaks.

Working in shade or on a cool, overcast day keeps the cleaner from drying too fast and leaving residue.

Removing Mold and Mildew

Mold and mildew are the most common composite complaints, especially in shaded, damp areas. They feed on organic debris trapped on the surface, not on the composite itself. To remove them:

• Use a composite-safe deck cleaner formulated for mold, or a mix of warm water and a small amount of white vinegar for light cases.
• Apply, let it sit a few minutes, then scrub with the soft brush.
• Rinse completely.

Keeping the deck swept and free of leaf litter is the best long-term defense, since mold needs organic matter to take hold.

Tackling Grease and Oil Stains

Grease from a grill or dropped food is a frequent problem near cooking areas:

• Blot up fresh grease immediately — don’t let it soak in.
• Apply a degreasing dish soap or a commercial composite cleaner directly to the spot.
• Scrub and rinse promptly.

Most capped composites shrug off grease if you act fast. Placing a grill mat under your barbecue prevents the problem entirely.

Rust, Berry, and Tannin Stains

Colored stains need targeted treatment:

• Rust from metal furniture or planters responds to a composite-safe oxalic-acid-based deck brightener. Avoid harsh acids that can lighten the boards.
• Berry, leaf, and tannin stains from overhanging trees usually lift with a cleaner formulated for organic stains; the sooner you address them, the better.
• Always test any specialty product on an inconspicuous spot first.

Can You Pressure Wash Composite Decking?

Yes, but carefully — and only if your manufacturer allows it. Improper pressure washing is the top cause of composite damage:

• Keep pressure at or below 1,500 PSI, and check your brand’s limit (some cap it lower).
• Use a fan tip, never a narrow jet.
• Hold the nozzle at least 8 to 12 inches from the surface.
• Spray along the length of the boards, not across the grain.

Too much pressure or a close nozzle can etch the surface, remove the cap, and permanently mar the finish — and that damage is not covered by warranty.

What to Avoid

Some habits do more harm than good:

• Wire brushes and steel wool scratch the cap and open the surface to staining.
• Bleach in high concentrations can lighten boards and harm surrounding plants; use only sparingly and diluted if the manufacturer permits.
• Abrasive pads and harsh solvents can dull the finish.
• Letting cleaner dry on the surface leaves streaks — always rinse promptly.

When in doubt, check your decking brand’s care guide, since using a prohibited method can void the warranty.

Preventing Stains and Buildup

The easiest cleaning is the cleaning you never have to do:

• Sweep regularly to keep leaves and debris from decomposing on the surface.
• Clear gaps between boards so water and debris drain freely.
• Use furniture pads and a grill mat.
• Trim back overhanging branches that drop berries, sap, and leaves.
• Rinse off pollen in spring before it bonds to the surface.

Restoring Faded or Weathered Boards

Even quality composite can look tired after years of sun and weather. Before assuming the boards are ruined, try a thorough restoration:

• Do a deep clean with a dedicated composite deck cleaner to strip away the film of grime, pollen, and mildew that dulls the color.
• Scrub the full surface evenly so you don’t leave clean and dirty patches.
• Rinse completely and let the deck dry to reveal the true condition underneath.
• For uncapped composite that has genuinely faded, some manufacturers permit a composite-specific stain or restorer designed for their product — never use ordinary wood deck stain, which won’t bond properly.

A surprising number of “worn out” decks simply have years of built-up grime hiding their real color, and a proper cleaning brings them back to life.

Tackling Sunscreen, Food, and Drink Stains

Summer entertaining brings a specific set of spills. Handle them promptly:

• Sunscreen and bug spray can leave oily marks — clean with warm soapy water or a degreaser as soon as you notice them.
• Wine, coffee, and juice should be blotted and washed quickly before they set.
• Grease from food responds to a degreasing dish soap.

The faster you address these spills, the less chance they have to bond with the surface and become permanent.

Winter and Snow Removal

Cold-weather care matters too. Use a plastic shovel, not a metal one, and shovel along the board length. For ice, use calcium chloride or rock salt only if your manufacturer approves; some ice melts can leave residue. Sand for traction is a safe, surface-friendly option.

Capped vs. Uncapped Composite

How you clean depends partly on which generation of composite you have:

• Capped composite has a hard polymer shell that resists stains and moisture. It cleans easily with soap and water and rarely stains permanently.
• Uncapped (first-generation) composite has an exposed wood-fiber surface that’s more prone to mold, fading, and staining, and needs more diligent cleaning.

If your deck is older uncapped material, be extra consistent about sweeping and washing, since its porous surface holds onto grime and feeds mold more readily.

Removing Ice Melt and Salt Residue

After winter, deicing products can leave a white, chalky film on the boards. To clear it:

• Rinse thoroughly with the hose once temperatures allow.
• Wash with warm, soapy water and a soft brush to lift residue.
• For stubborn film, a composite-safe cleaner formulated for salt and mineral deposits works well.

Cleaning off salt promptly in spring prevents it from dulling the finish over the season.

Seasonal Cleaning Schedule

A simple calendar keeps the deck looking its best year-round:

• Spring: a full wash to remove winter grime, pollen, and any salt residue.
• Summer: spot-clean grease and food spills promptly, and rinse as needed.
• Fall: a second full wash and thorough sweep before leaves accumulate.
• Winter: shovel snow with a plastic shovel and keep debris off the boards.

Consistency beats intensity — regular light cleaning prevents the deep stains that require aggressive treatment.

Final Thoughts

Keeping composite boards looking their best comes down to a consistent, gentle routine. Cleaning composite decking twice a year with soap, warm water, and a soft brush handles most grime, while targeted cleaners tackle mold, grease, and colored stains. If you pressure wash, stay under 1,500 PSI with a fan tip held well back. Avoid wire brushes and harsh chemicals, sweep often to deny mold its food source, and address spills quickly. Follow these methods and your composite deck will hold its color and stay inviting for the full length of its long warranty.