How to Safely Clean a Composite Deck (Without Ruining It)

If you have a composite deck, you already know the significant investment required to install it. Because these materials are marketed as low maintenance, it often comes as a surprise to homeowners when their beautiful outdoor space becomes covered in dirt, mold, and mildew.

Even more surprising? You cannot safely clean them with a standard power washer.

The Danger of High-Pressure Washing

Leading composite decking brands like Trex, Azek, and TimberTech are manufactured using a blend of plastic and wood fibers. Newer generations of these materials feature a composite core protected by a finished outer cap that mimics the look of real wood.

While durable against foot traffic, this outer cap is actually quite soft. Blasting it with high pressure will score the material and destroy your deck in short order. Most manufacturers strictly recommend using less than 600 PSI at a distance of at least 10 inches from the surface.

Because the most common pressure washers sold or rented to homeowners blast water at 2,000 PSI or higher, they are completely unacceptable for cleaning composite decks. Every year, we receive calls from homeowners asking us to fix damage caused by a DIY cleaning attempt or an uneducated contractor. Unfortunately, once a composite deck is etched or scarred by high pressure, the damage is permanent.

Why Does Mold Grow on Composite Decks?

Mold and mildew thrive in damp environments and will readily grow directly on the deck’s surface or on organic materials (like pollen and fallen leaves) resting on top of it. This organic growth leaves behind black streaks and green patches that make your expensive deck look dirty and aged.

The Professional Solution: Hot Water Soft Washing

Trying to clean it yourself or hiring a contractor who lacks specific knowledge in composite deck cleaning is a massive risk. Professionals use a method called soft washing, which relies on hot water, manufacturer-approved cleaning solutions, and very low pressure.

Here is the professional process for restoring a composite deck:

1. Property Protection: We thoroughly wet the deck and all surrounding bushes and landscaping with fresh water to protect them from overspray.

2. Targeted Treatment: We apply a specialized cleaning solution to the deck boards and railings. This achieves a 100% kill ratio on all mold, mildew, and algae root systems.

3. Rail Scrubbing: We apply a dedicated soap solution to the rails and gently scrub them to remove black streaks, whitening them up so they look brand new.

4. Low-Pressure Rinse: A thorough, high-volume rinse safely washes away all the dirt, suspended debris, and dead mold.

The Equipment Needed to Do It Right

If you attempt this yourself, you must be properly equipped. To safely clean a composite deck, you will need:

• A low-pressure hot water power washer. (Cold water will work in a pinch, but it is far less effective at cutting through organic buildup).

• A safe application method for your bleach and soap solution. The best option is a dedicated soft wash pump or chemical injector; a pump sprayer is the least advised method.

• A soft-bristle brush attached to a broom handle.

• A water connection capable of delivering at least 6 gallons per minute for safe rinsing.

• Proper PPE: A respirator designed to protect against chlorine inhalation, protective eyewear, long rubber gloves, rubber boots, and rain gear.

Step-by-Step Cleaning Guide

1. Pre-wet all surrounding bushes, grass, and vegetation to protect them.

2. Cool the surface by wetting the deck if it is sitting in direct sunlight.

3. Apply the detergent evenly, ensuring you never let the solution dry on the boards.

4. Rinse the deck using less than 300 PSI, keeping the nozzle at least 10 inches away from the surface.

5. Final rinse all siding and surrounding vegetation.

When done correctly, you will have a beautifully restored deck ready for you to enjoy all season long.

Want to skip the hassle and eliminate the risk of accidental damage? We provide The Best Service Anywhere™ for homeowners looking to protect their investment. [Link: Contact A+ Power Washing and Roof Cleaning today for a free estimate!]