How to Remove Mold from Trex Decking

Trex decking, a popular composite material blending wood fibers and plastic, offers durability and low maintenance but can develop mold and mildew in damp environments. These fungal growths appear as black, green, or gray spots, compromising appearance and safety. Effective cleaning restores the surface while preventing future issues.

Why Mold Thrives on Composite Decks

Mold and mildew flourish in moist, shaded areas with poor airflow. Trex decking’s textured surface traps moisture, pollen, and organic debris, creating ideal conditions for growth. Unlike wood, composites resist rot but not surface fungi. Regular exposure to rain, humidity, or leaf buildup accelerates problems, especially in humid climates.

Untreated mold spreads quickly, potentially weakening the material’s capstock layer over time. Early intervention preserves warranty and extends lifespan up to 25-50 years, as per manufacturer guidelines.

Essential Tools and Materials for Cleaning

Gather these items before starting:

• Soft-bristle brush or broom (avoid wire brushes to prevent gouging)
• Garden hose with adjustable nozzle or low-pressure washer (under 1500 PSI)
• Spray bottle or pump sprayer for cleaners
• Protective gear: gloves, goggles, mask
• Buckets for mixing solutions
• Clean rags or microfiber cloths for spot treatment

Invest in quality tools to avoid surface damage. Trex recommends fan-tip nozzles held 6-8 inches from boards for rinsing.

Step-by-Step Mold Removal Process

1. Preparation and Safety First

Clear furniture, plants, and debris from the deck. Sweep thoroughly, using a putty knife for gaps. Rinse with a hose to remove loose dirt. Work on a dry day; wet decks reduce cleaner efficacy. Cover nearby plants with plastic sheeting to protect from runoff.

2. Choose the Right Cleaning Solution

Select based on severity:

Bleach kills surface mold effectively but may lighten colors; dilute for darker Trex. Oxygen alternatives are safer for plants and warranties.

3. Apply and Agitate

Spray solution evenly on affected areas. Let dwell 10-15 minutes without drying. Gently scrub with soft brush in circular motions, focusing on grooves. Avoid aggressive pressure to preserve texture.

4. Rinse Thoroughly

Hose off from top to bottom, using wide fan spray. Ensure no residue remains, as it can attract dirt. Repeat for stubborn spots.

5. Dry and Inspect

Allow 24-48 hours to air dry. Check for missed areas and reapply if needed. Deck should look uniform and refreshed.

Advanced Cleaning for Stubborn Mildew

For persistent black streaks or Gen-1 Trex, combine methods. Start with 2% sodium hypochlorite (SH) solution via pump sprayer, dwell, then low-pressure rinse (500-1000 PSI). Follow with oxalic acid brightener for tannin stains mimicking mold. Test in inconspicuous spots first.

Power washing alone removes visible growth but not roots; pair with fungicides. Users report success with TSP-bleach mixes (1 cup each per gallon hot water), standing 10 minutes before rinsing.

Preventing Mold Regrowth on Trex Surfaces

Prevention beats repeated cleaning:

• Improve Drainage: Ensure 1/8-inch slope per foot; clear clogged gaps yearly.
• Trim Vegetation: Keep plants 18 inches from deck edges for sunlight and airflow.
• Quarterly Washes: Hose off debris; annual deep clean in spring.
• Sealant Application: Use Trex-approved enhancers post-cleaning to repel water.
• UV Protection: Composite fades less but mold inhibitors in newer lines help.

Store cushions elevated; avoid standing water. In high-humidity areas, fans or dehumidifiers aid drying.

Common Mistakes to Avoid

• High-pressure washing (>3100 PSI) etches boards.
• Mixing bleach with ammonia creates toxic gas.
• Ignoring warranties: Trex voids coverage for unapproved chemicals.
• Skipping protection: Runoff harms grass, pets.
• Over-scrubbing: Strips protective cap.

Trex Decking Maintenance Schedule

Frequently Asked Questions (FAQs)

Can I use a pressure washer on Trex decking?

Yes, but limit to 1500 PSI with fan tip, 8 inches away. Higher risks damage.

Is bleach safe for Trex warranties?

Diluted yes, but check model; some void for oxidizers. Opt for approved cleaners.

How long does mold removal last?

6-12 months with prevention; reapply seasonally in wet climates.

What if mold returns quickly?

Improve ventilation, drainage; use penetrating sealants.

Are natural cleaners effective?

Vinegar/baking soda works for light mildew; bleach for heavy infestations.

Professional vs. DIY Cleaning

DIY suits most; hire for large decks or heavy buildup. Pros use commercial-grade soft washing, saving time. Cost: $0.50-$2 per sq ft professionally.

Track progress with photos; consistent care yields like-new results years later.