How to Clean Composite Deck | Done in 6 Steps

A dirty composite deck collects leaves, pollen, and mildew that turn the surface slick and dull. But unlike wood, composite can’t be sanded or stained back to new—so the cleaning method matters. Use the wrong brush or bleach, and the surface stains permanently. Here’s the six-step process that keeps your deck looking like the day it was installed.

What You Need to Clean Your Composite Deck

The right tools prevent damage. Composite manufacturers publish specific rules for brushes and cleaners, and those rules vary by brand.

• Brushes: Soft-bristle for routine cleaning. Never use metal brushes—they scratch the surface.
• Cleaners: Mild dish soap (2 tablespoons Dawn per gallon of warm water) or an oxygenated cleaner like Simple Green Oxy Solve mixed 1:20 with water. Use only manufacturer-approved cleaners for specific brands. Never use bleach, SLR, sugar soap, or harsh acids.
• Pressure washer: Optional and only if the manufacturer explicitly allows it. Maximum 1500 PSI, fan nozzle, 12 inches from the surface. Many manufacturers recommend against pressure washers entirely—they can reduce deck lifespan.
• Rinse tool: Garden hose with a spray nozzle. Pressure from the hose is usually sufficient.

The 6-Step Cleaning Process

Work in small sections—roughly 10 by 10 feet at a time—so the cleaner never dries on the boards. Dried cleaner leaves a sticky film that is difficult to remove.

1. Clear and sweep. Remove all furniture, planters, and rugs. Sweep thoroughly, focusing on corners and board gaps. Use a putty knife for stuck debris.
2. Pre-rinse. Spray the surface lightly with a garden hose to loosen surface dirt and protect nearby plants from overspray.
3. Apply cleaner. Mix the solution according to manufacturer instructions. Apply generously with a sprayer or sponge mop and let it dwell for 30–60 seconds (TimberTech) or 3–5 minutes (Simple Green). Do not let it dry.
4. Scrub. Scrub firmly in the direction of the board grain.
5. Rinse immediately. Rinse the section thoroughly with the hose before the solution dries. Continue until no suds remain. Dried cleaner leaves a film that attracts more dirt.
6. Dry. Let the deck air dry completely before returning furniture. A leaf blower speeds up drying and prevents water spots.

How to Handle Stubborn Stains

Routine sweeping and spot cleaning handle most issues. For stains that resist standard cleaning, each type has a specific cure.

Oil, grease, and food: Clean immediately with warm soapy water and a non-metal brush. For tough spots, apply dish detergent directly to the stain, let it sit for 15–30 minutes, then scrub. Mold and mildew: Use an oxygenated cleaner only. Bleach discolors composite and kills the surface layer. Tough stains that survive standard cleaning: This is a last resort—sanding removes a thin layer of the surface finish and should only target the stained spot.

For the most common stain types, a dedicated cleaner designed for composite surfaces often works better than dish soap. If you’re shopping for a product, see our tested roundup of the best composite deck washes for cleaner options that are safe for your specific brand.

Cleaning Frequency

A consistent schedule prevents buildup that takes hours to remove later. Sweep leaves and debris weekly. Perform a deep clean at least twice per year—once in spring after winter grime and once in fall before leaves accumulate.

Common Mistakes That Damage Composite

• Letting cleaner dry on the deck: The most critical error. Re-wet the area immediately if the solution starts to dry.
• Scrubbing against the grain: Causes permanent streaking.
• High-pressure washing: Exceeding 1500 PSI or holding the nozzle closer than 12 inches damages the surface.
• Using bleach: Discolors and degrades composite materials permanently.
• Inadequate rinsing: Soap residue attracts dirt and causes discoloration over time.