Hi, I’m Scott Paul, a licensed exterior restoration contractor with over 30 years of experience and 10,000+ deck restorations. This review of how to clean composite decking is based on my own hands-on field testing, not manufacturer claims. See my full credentials and testing stats here.
Composite decking is low maintenance, not no maintenance. Dirt, pollen, black algae, and mildew build up on the surface and in the texture of the boards, especially on shaded decks and decks near trees. The right composite deck cleaner and a stiff brush will bring most composite decks back in an afternoon, while the wrong product can fade or permanently mark the boards. This guide covers what works on Trex, TimberTech, Azek, and other composite brands, what damages composite, and which products I use.
- Use an oxygen bleach cleaner like DEFY Composite Deck Cleaner to safely lift black algae, mildew, and dirt from composite boards.
- Avoid chlorine bleach, high-pressure washing, solvents, and sanding, as these can permanently damage or fade composite boards.
- Follow a 7-step cleaning process: sweep, wet, mix, apply, dwell 15 to 20 minutes, scrub, and rinse thoroughly for best results.
- Older, uncapped composite boards absorb moisture and fade faster, often benefiting from a clear composite deck sealer after cleaning.
- Clean composite decking at least twice a year, in spring and fall, with shaded or tree-lined decks needing a third cleaning.
In this guide:
- What Is the Best Cleaner for Composite Decking?
- Composite Deck Cleaning Products Compared
- How to Clean Composite Decking in 7 Steps
- Cleaning Trex, TimberTech, Azek, and Older Composite
- What Damages Composite Decking
- Restoring and Sealing Composite After Cleaning
- How Often to Clean Composite Decking
- Composite Deck Cleaning FAQ
What Is the Best Cleaner for Composite Decking?
The best cleaner for composite decking is an oxygen bleach cleaner made for composite. Oxygen bleach (sodium percarbonate) foams as it works, lifting black algae, mildew, and ground in dirt out of the surface texture instead of just bleaching the stain lighter. It is biodegradable and much safer for nearby plants than chlorine bleach.
The composite deck cleaner I use is DEFY Composite Deck Cleaner. It is a powdered concentrate that mixes with warm water, and one 2 lb. container makes 6 gallons of solution, enough to clean 600 to 1,200 sq. ft. It is compatible with Trex, TimberTech, Azek, Fiberon, Evergrain, Duradeck, ChoiceDek, CorrectDeck, and other composite and vinyl decking.
Composite Deck Cleaning Products Compared
These are the composite deck cleaning products and methods people try most often, and how each one performs on composite.
| Cleaning Solution | Removes Mold and Algae | Safe for Composite | My Verdict |
|---|---|---|---|
| Oxygen bleach composite cleaner | Yes | Yes | Best choice for regular cleaning and black spots |
| Dish soap and water | No | Yes | Fine for light dirt and spills only |
| Pressure washing alone | Partly | Only at low pressure | Use only to rinse a cleaner, never as the cleaner |
| Chlorine bleach | Bleaches it lighter | Risky | Avoid: can fade boards and harms plants |
How to Clean Composite Decking in 7 Steps
- Clear and sweep the deck. Move furniture, grills, and planters, then sweep leaves and debris off the boards and out of the gaps. Debris in the gaps holds moisture and feeds mold.
- Wet the deck and nearby plants. Rinse the composite boards and soak surrounding plants with water. A wet surface helps the cleaner spread evenly.
- Mix the cleaner. Dissolve ¾ cup of oxygen bleach composite deck cleaner per gallon of warm water. Warm water dissolves the powder faster and activates the foaming action.
- Apply the solution. Apply with a pump sprayer, mop, or deck brush, working in sections and keeping the surface wet. If you use a sprayer, filter the solution through cheesecloth first so undissolved powder does not clog the nozzle.
- Let it dwell. Let the cleaner foam and work for 15 to 20 minutes without drying. Add more solution to any area that starts to dry.
- Scrub. Scrub with a stiff bristle deck brush along the length of the boards, with extra passes on black spots and shaded areas.
- Rinse thoroughly. Rinse with a garden hose or a low pressure fan tip until no cleaner residue remains, then let the deck dry. Heavy mold or algae may need a second application.
Cleaning Trex, TimberTech, Azek, and Older Composite
Most composite decking sold today is capped, meaning the wood and plastic core is wrapped in a protective plastic shell. Capped boards from Trex, TimberTech, and similar brands, along with Azek PVC decking, hold dirt and mildew on the surface, so regular cleaning with an oxygen bleach cleaner is usually all they need. Always check your brand care guide before pressure washing, since limits vary by manufacturer.
Older, first generation composite boards are uncapped, so the wood fibers in the board are exposed. These boards absorb water, grow mold more readily, and fade over time. They clean up well with the same process, but they often look blotchy or faded afterward, which is where a composite deck sealer helps.
What Damages Composite Decking
- Chlorine bleach: Can fade or discolor some boards and damages surrounding plants.
- High pressure and narrow tips: A zero degree tip or high pressure held close can etch the surface or cut through the cap.
- Sanding: Exposes the core, leaves permanent scuff marks, and usually voids the warranty.
- Solvents and acetone: Can soften or stain the plastic surface.
- Metal shovels and ice chippers: Gouge the boards. Use a plastic shovel in winter.
- Rubber backed mats: Trap moisture and can discolor the boards underneath.
Restoring and Sealing Composite After Cleaning
A composite deck restorer usually means two steps: a deep cleaning, then a clear sealer for faded or older boards. After cleaning with an oxygen bleach cleaner, a clear composite sealer like DEFY Composite Deck Sealer can restore color, add water repellency, and slow mold regrowth on uncapped boards. See my composite deck sealer reviews for the products I have tested. Newer capped decking generally does not need a sealer, only regular cleaning.
How Often to Clean Composite Decking
Clean composite decking at least twice a year: once in spring to remove winter grime, pollen, and mildew, and once in fall before leaves settle in. Decks in heavy shade, near trees, or close to water may need a third cleaning. Sweeping regularly and keeping the gaps clear will stretch the time between deep cleanings.
Composite Deck Cleaning FAQ
What is the best cleaner for composite decking?
An oxygen bleach cleaner made for composite, such as DEFY Composite Deck Cleaner. It lifts black algae, mildew, and dirt out of the surface without the damage and plant harm that chlorine bleach can cause.
Can you use bleach on composite decking?
Avoid chlorine bleach. It can fade and discolor some composite boards and harms nearby plants. Oxygen bleach cleaners are safer and lift stains instead of just bleaching them.
Can you pressure wash composite decking?
Most manufacturers allow low pressure washing with a fan tip held well away from the surface, but check your brand care guide. A cleaner and a stiff brush do most of the work, so high pressure is never needed.
How do you remove black spots from composite decking?
Black spots are usually mold or algae. Apply an oxygen bleach composite cleaner, let it dwell 15 to 20 minutes, scrub with a stiff bristle brush, and rinse. Heavy growth may need a second application.
Can you seal composite decking?
Yes. Older and uncapped composite boards benefit from a clear composite deck sealer after cleaning, which restores color and slows mold. Newer capped boards usually only need regular cleaning.
How often should you clean composite decking?
Clean composite decking at least twice a year, in spring and fall, and more often on shaded decks or decks near trees.
Have a question about cleaning your composite deck? Tell me the brand and age of your decking in the comments below, and I will help you pick the right approach.
