Deck Cleaning and Restoration Guide: Wood and Composite Care

A clean deck is safe and looks good. Algae and mold make it slippery and dangerous. Proper preparation is essential for staining. But different materials need fundamentally different approaches.

Understanding Your Deck Material

Wood Decks

Pressure-treated pine is the most common and affordable option. Cedar and redwood are expensive but beautiful and naturally rot-resistant. Tropical hardwoods like ipe and mahogany last for decades but are difficult to work with. Exotic hardwoods vary widely in cost and characteristics.

Wood absorbs water, which causes swelling, warping, and cracking with moisture changes. It grows mold, algae, and mildew in damp conditions. UV light grays the surface over time. Wood needs regular maintenance—annual cleaning and periodic staining to protect the investment. Splinters develop if cleaning techniques aren’t careful.

See our wood deck cleaning guide for wood-specific techniques and pressure settings.

Composite Decking

Composite is wood fibers mixed with recycled plastic. Major brands include Trex, Fiberon, and TimberTech. It doesn’t need staining, resists rot and insects, and lasts 25+ years with manufacturer warranty. It’s expensive—typically more than wood—but low-maintenance.

However, composite isn’t maintenance-free. It grows mold on the surface. UV causes fading. Scratches show more than they do on wood. Some brands develop chalky surfaces over time.

Critical: Read your composite manufacturer’s cleaning instructions before starting. Some brands prohibit pressure washing entirely. Some prohibit bleach. Using the wrong method voids the warranty. Our composite decking guide covers brand-specific approaches in detail.

Wood Deck Cleaning Process

Check the deck structure before cleaning. Look for loose boards, soft rotted spots, and structural issues—ledger board attachment, joist condition, support post integrity. Check for rusty or loose fasteners and surface condition like peeling stain, gray weathering, and algae growth. Fix these before cleaning. Cleaning rotten or loose decks makes problems worse, not better.

Light Maintenance Cleaning

For regular maintenance, mix 8 ounces of 12.5% sodium hypochlorite per 5 gallons of water with surfactant. Apply with pump sprayer, let sit 3–5 minutes, lightly agitate with soft brush if needed, rinse with white nozzle (40°) staying 18+ inches away. This removes light dirt, mildew, and surface algae.

Restoration Cleaning for Weathered Decks

Mix 16 ounces of 12.5% sodium hypochlorite per 5 gallons of water with surfactant. Pre-wet landscaping first. Apply the mix liberally, scrub with the grain using a stiff brush, let sit 5–8 minutes, rinse with white nozzle staying 12–18 inches away. This removes gray weathering and kills algae thoroughly.

Brightening for Stain Preparation

Clean the deck first using the restoration method above. Then apply oxalic acid brightener following product directions exactly. Let sit 15–20 minutes, lightly agitate, and rinse thoroughly. This restores natural wood color and opens wood pores for better stain penetration.

For railings and spindles, use lower pressure (white nozzle only), protect surfaces below with tarps, and clean from bottom up with chemicals, then rinsing from top down.

The underside of the deck often holds mold and mildew. It’s frequently neglected, but clean it if you can access it safely. Protect landscaping below with tarps.

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Composite Deck Cleaning Process

Read the manufacturer’s cleaning instructions first. Many brands prohibit pressure washing. Some prohibit bleach. Using the wrong method voids the warranty.

Routine Cleaning

Sweep debris. Mix warm water with mild dish soap (1–2 ounces per gallon). Scrub with soft brush. Rinse with garden hose at low pressure. No pressure washer is needed for routine cleaning.

Mold and Mildew Treatment

Pre-wet landscaping. Apply 8 ounces of 12.5% sodium hypochlorite per 5 gallons of water (verify your brand allows this—some prohibit bleach entirely). Let sit 5–10 minutes. Light agitation with soft brush only. Rinse thoroughly with garden hose at low pressure. Alternatively, use a commercial composite deck cleaner following manufacturer instructions exactly.

Tough Stains and Chalky Surfaces

Use commercial composite deck cleaner following manufacturer instructions precisely. You may need multiple applications. For serious stains, hire a professional with specialized equipment and brand knowledge.

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Post-Cleaning: Wood Decks

If the wood absorbs water (darkens when wet), has surface cracking, has peeling stain, or you want to restore appearance, stain it. Pressure-treated wood doesn’t require staining—natural weathering is fine if you prefer that look.

Wait 48–72 hours for the wood to dry completely, then apply stain per manufacturer instructions. Reapply every 1–3 years depending on the product and climate.

Post-Cleaning: Composite Decks

No staining is needed or allowed on composite decks. Optional UV-protective spray or mold inhibitors might help, but check the manufacturer first. Some products claim to restore faded color. Verify your brand approves any product before applying.

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Common Mistakes to Avoid

Too much pressure on wood: High PSI with aggressive nozzles damages wood fibers, creating a fuzzy surface that takes weeks of hand sanding to repair. Use white nozzle only, stay 18+ inches back.

Working against the grain: This raises fibers, creates a rough surface, and makes staining difficult. Always work with the grain direction.

Not letting chemicals dwell: Chemicals need time to work. If you don’t let them sit long enough, you’ll need to redo the whole job. Let them sit 5–10 minutes minimum.

Letting chemicals dry: Dried chemicals leave residue, streaking, and hazing. Work in sections. Keep the surface wet with periodic misting.

Wrong chemicals on composite: This voids the warranty and causes permanent damage. Read manufacturer instructions before starting.

Not pre-wetting landscaping: Harsh chemicals kill plants. Pre-wet plants thoroughly with clean water before treating the deck.

Cleaning rotted wood: This makes it worse, accelerates decay, and creates a safety hazard. Inspect first. Replace damaged boards before cleaning.

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When to Hire a Professional

Hire a professional if you see structural issues: ledger board pulling away, rotted joists or posts, extensive board damage. Multi-level decks, decks under trees with constant debris, heavily covered by plants, or extremely weathered decks often benefit from professional help.

If you’re unsure about composite cleaning methods or have stubborn stains, hire someone. Professionals document their work, which protects warranty coverage.

Wood deck cleaning typically costs $200–350 for a 12×16 deck. Composite costs $250–400. Add $100–200 for brightening. Staining adds $300–600 per coat. Multi-level or difficult-access decks cost 30–50% more.

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Maintenance Schedule

Wood decks: Light cleaning annually. Full cleaning every 2–3 years. Stain every 2–5 years depending on the product. Check fasteners annually.

Composite decks: Light cleaning (soap and water) twice a year. Full inspection annually. Deep clean for stubborn stains as needed.

For both: Sweep regularly. Move furniture periodically. Keep gaps clear of debris. Address mold early. Trim overhanging plants and branches.