8 Tips and Products for Cleaning Composite Decking

Updated: May 17, 2023

If you use your deck a lot or are planning an outdoor party, you may be wondering how to clean composite decking. Start by checking out these tips.

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compost Deck after being cleaned
oneillbro/Getty Images

When to Clean the Deck

You should clean your composite wood deck once or twice a year on a calm, sunny day. This gives the cleaner time to do its work within the texture of the composite before rain or wind drive you inside.

However, if you’re working in direct sunlight, work in small sections. This prevents the cleaner/water solution or other products from drying up before you can wash them off.

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compost deck furniture
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Prep the Deck for Cleaning

First, cover any plants, grass, yard ornaments or other items that are near or under your deck to protect them from cleaning products. Keep in mind that plants or grass kept under cover for too long may die.

Next, clear the deck of furniture, debris and general dirt. Remove tables, chairs, grills, rugs, potted plants and anything else. Sweep up branches, leaves and other debris from the surface, including the corners. Use a wide putty knife or attach a hook to the end of a broom handle to dig out dirt and leaves from the crevices. Then hose down the deck to wash away loose dirt and debris.

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liquid detergent
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Clean the Deck with Liquid Detergent and Water

A composite deck typically needs just a good cleaning with soapy water and a scrub brush to remove most surface stains and layers of dirt that accumulate.

In a bucket, mix a gallon of warm water with 1/4-cup liquid dish detergent, such as Dawn, which is biodegradable, non-toxic for humans and animals and contains no phosphates. It’s gentle enough that it won’t damage the surrounding environment or your skin, yet strong enough to pull dirt from the textured grain of composite decking. You can even try out some Dawn powerwash spray for an effective Dawn alternative.

Dunk a long-handled or handheld brush into the bucket and scrub the boards. Scrub in the direction of the grain of the plank in small sections across the deck.

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Siga Brush
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Remove Oil and Grease Spots with Detergent

For grease and oil stains, apply a few drops of liquid dish detergent such as Dawn. This will power through the grease and lift it from the surface without damaging the composite decking.

Use a handheld scrub brush dipped in warm water to whisk away the oily stain. To prevent streaking, move quickly so the detergent dry on the surface and leave a film. Wash the dirty, soapy residue away with a few squirts of the garden hose.

“While the coating on composite decking will help keep many stains to just (on) the surface, it is always a good idea to clean up spills of any kind, as quickly as possible,” says Kevin Busch, vice president of operations at Mr. Handyman, a Neighborly company. “The longer they sit, the more likely they will seep into the decking and be tougher to remove.”

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cleaning wooden terrace planks with high pressure washer
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Clean the Deck with a Pressure Washer

A pressure washer can remove embedded dirt without a cleaning product, but it’s not always advisable. If not used properly, the high water pressure can damage composite decking.

“Pressure washers can generally be used on composite decking but often they can be cleaned without one,” Busch says. “Combining warm soapy water a deck brush, and some old-fashioned elbow grease will usually do the trick and help you avoid potentially damaging your deck.”

A quick spray of the surface with the pressure washer fan tip will freshen a deck and remove a light layer of dirt. The fan tip lowers the pressure from the nozzle and lessens the chances of damage.

“In general, stay below 1,500 psi (pounds per square inch),” Busch says. “Keep the nozzle back from the deck boards by at least six inches for the same reasons. Be sure to move in broad, sweeping motions, moving with the grain of the board.”

For decks with thick layers of dirt and stubborn stains, fill the pressure washer soap dispenser with Dawn or a product specifically for a pressure washer. Read the manufacturer’s directions for best results. Give stubborn stains a good scrub with a stiff brush and work the cleaner into the corners.

Wash down the deck with plain water using the widest pressure washer nozzle. Make wide, sweeping motions with the nozzle about two feet above the surface of the deck.

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Mold Armor
via amazon.com

Remove Mold and Mildew With Armor E-Z Deck

Within minutes of application, Mold Armor E-Z Deck, Fence and Patio cuts through unsightly splotches of mold and mildew. This bleach-based product cleans, brightens and kills mold and mildew without scrubbing.

Attach the hose-end adapter to a garden hose and spray evenly on the affected area. Wait 10 minutes before washing the cleaning solution off with plain water from the garden hose.

Note: Because this is a bleach-based product, be cautious. Apply a small amount on a hidden or out-of-the-way area before you begin to ensure it doesn’t discolor your deck boards.

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Oxy Clean
via amazon.com

Remove Tree Sap With Simple Green Oxy

Sticky spots of tree sap on your composite deck can be impossible to scrub away with soap and water. For that you need a solvent such as Simple Green Oxy Solve.

This concentrate, which can be applied with a pressure washer or in a bucket, relies on peroxide rather than harsh chemicals to cut through sap, thick grime and oils. The manufacturer says Simple Green Oxy Solve will lift sap from a composite deck in one application, without bleaching or damaging it.

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via target.com

Clean Rust Stains with WD-40

A spritz of the multi-purpose lubricant WD-40 loosens rust by penetrating through its porous layer without damaging the deck underneath.

Spray the WD-40 on the rust stain, let it sit for 10 minutes, then wipe up with a clean, dry cloth. Wash away the WD-40 with detergent and water. If any bits of rust remain, remove them with a brush or sponge. WD-40 to the rescue, again!

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