Can You Power Wash Composite Decking? [Safe Cleaning Guide]
Yes, you can power wash composite decking, but only if it’s done carefully and with the right technique. Using too much pressure or the wrong nozzle can cause permanent damage to your boards. In this guide, you'll learn exactly how to clean your composite deck safely using a power washer, including expert tips on PSI settings, tools, cleaning products, and what to avoid.
Why Composite Decking Needs Special Care
Composite decking isn’t like traditional wood. While it’s built to be more durable and lower maintenance, it still needs the right kind of cleaning.
Many people assume they can treat it just like regular lumber, but using too much water pressure or the wrong cleaning products can do more harm than good. Let’s break down why.
What Is Composite Decking Made Of?
ComComposite decking is made from a mix of recycled wood fibers and plastic. This blend gives it a sleek, modern look and helps it resist common issues like rotting, warping, and insect damage.
But that smooth surface and durable core come with a trade-off: it’s not as forgiving when it comes to aggressive cleaning. Unlike natural wood that can be sanded down or repaired, composite materials can scar or stain permanently if you're not careful.
Think of it like this: composite decking is tough, but not bulletproof. Using the wrong tools or pressure can easily ruin the surface, and there's no quick fix if that happens.
Why Pressure Washing Can Be Risky
Here’s the thing about power washers: they’re strong. That’s great for blasting grime off concrete, but it can be too much for your deck. If you use too much PSI (pounds per square inch), get too close to the surface, or aim the spray directly without spreading it out, you can:
- Etch or scratch the finish
- Strip away the protective coating
- Cause splintering or streak marks
- Push water deep into seams, which can lead to mold
And unlike wood, composite decking can’t just be sanded down to remove surface damage. That’s why it’s so important to understand the right way to power wash your composite deck, and that’s exactly what we’ll walk you through next.
How to Power Wash Composite Decking Safely
Power washing your composite deck can be a great way to restore its clean, like-new appearance, if you follow the right steps. Done incorrectly, it can damage the boards beyond repair.
Below is a safe, step-by-step process that we at SWKS Power Washing follow every time we clean a composite deck in Southwest Kansas.
1. Prep the Decking Area
Before you even pull out the pressure washer, you need to prep your space.
- Remove all furniture, grills, planters, and décor. Carefully lift items off the deck to avoid scraping or scratching the surface.
- Sweep the entire deck. Use a soft-bristle broom to clear leaves, dust, and loose debris, especially in corners and between grooved boards.
- Inspect for any cracks or surface damage. Make a note of soft spots or warped boards so you can work around them with extra care.
2. Use the Right Equipment
Using the wrong settings or nozzle can quickly damage composite decking. Here’s what we recommend:
- Use a pressure washer rated between 1,000 and 1,500 PSI. Anything higher could etch or scar the boards.
- Attach a 40-degree fan tip nozzle. This spreads the water out over a wider area, which helps prevent surface damage.
- Stick to cold or lukewarm water. Hot water can affect the structural integrity of composite materials.
💡 Pro Tip: Always test your washer on a small, hidden section before starting the full deck.
3. Apply a Deck-Safe Cleaner
While pressure alone can help, combining it with a safe cleaning solution gives better results, especially if your deck has mold, mildew, or built-up grime.
- Use a composite-safe cleaner. Products like OxiClean, Simple Green, or Owatrol Compo-Clean are gentle but effective.
How to apply:
- Mix the cleaner according to the label
- Use a garden sprayer or watering can to apply it evenly
- Let it sit for 5–10 minutes (don’t let it dry out)
Avoid using bleach or harsh chemicals as these can discolor the deck and break down the composite material over time.
4. Wash Along the Grain
This part is critical: always clean in the direction the boards run.
- Hold the nozzle about 12 inches above the surface.
- Follow the natural grain or grooves of the boards.
- Work in small sections, moving slowly and consistently to prevent streaks or missed spots.
This method helps with proper drainage and lifts out embedded dirt without scarring the boards.
5. Rinse & Dry Thoroughly
Once you're done cleaning:
- Rinse the deck well using clean water to remove any remaining soap or debris.
- Check for pooling water. If necessary, use a squeegee or broom to guide water off the surface.
- Let it air-dry fully before returning furniture or walking heavily on it.
Common Mistakes to Avoid
Power washing a composite deck might seem simple, but doing it the wrong way can lead to costly and irreversible damage. Here are some of the most common mistakes homeowners make, and what you should avoid to keep your deck in great shape.
Too Much Pressure
Using a pressure washer that's too powerful is one of the quickest ways to ruin composite decking. If the PSI is too high, it can gouge, scratch, or strip the surface.
The safe range is between 1,000 and 1,500 PSI. Anything higher can cause visible damage that can’t be repaired without replacing the boards. Always start on the lowest setting and only increase if absolutely necessary — and even then, cautiously.
Wrong Nozzle or Tip
A narrow or zero-degree nozzle focuses the water into a pinpoint stream that can cut into composite material like a blade. These tips are designed for concrete or brick, never for decks.
Always use a 40-degree fan tip nozzle when cleaning composite decking. It spreads the water out more gently, reducing the risk of etching or splintering the surface.
Don’t Use Harsh Chemicals
Bleach and chlorine-based cleaners are too aggressive for composite decking. While they might kill mold, they also strip away the deck’s finish, fade the color, and may even weaken the internal structure over time.
Instead, stick with composite-safe cleaning solutions like OxiClean, Simple Green, or a mild dish soap mixed with water. These are effective without being harmful to the material or the environment.
Spraying Against the Grain
One easy mistake that causes streaking or poor cleaning results is spraying across the boards instead of along them.
Always move the spray in the direction of the board grain or grooves. This ensures even cleaning, better drainage, and less chance of forcing water into seams or gaps where it can cause swelling or mold growth.
Alternatives to Power Washing Composite Decking
Power washing is effective, but it’s not always necessary. In some cases, a gentler approach is better, especially for older decks or light maintenance. Here are three solid alternatives that get the job done without the risk of damage.
Soft Washing
Soft washing is a low-pressure cleaning method that uses eco-friendly detergents to break down dirt, mildew, and algae before gently rinsing it all away.
- Low pressure means there’s little risk of damaging your deck surface.
- Ideal for delicate areas or decks that only need a light refresh.
- Cleaner does the heavy lifting, not the water force.
Soft washing is commonly used by professionals for roof cleaning, siding, and decks — and it’s often the safest bet for composite materials.
Manual Scrubbing with Brush and Mild Soap
If your deck just has a little dirt, pollen, or a few footprints from weekend barbecues, a bucket of warm water and a soft brush can go a long way.
- Use a non-metal brush with soft or medium bristles.
- Mix in mild dish soap or a composite-safe cleaner.
- Scrub gently in the direction of the board grain.
This method is great for spot cleaning and regular maintenance, and it’s easier on your deck and your water bill.
Hiring a Professional Deck Cleaner
If you're unsure about pressure settings, don’t want to risk damaging your deck, or simply don’t have time, calling a professional is a smart move.
At SWKS Power Washing, we’ve cleaned dozens of composite decks across Southwest Kansas using the safest and most effective techniques. We know what pressure to use, which products work best, and how to protect your investment while getting the best possible results.
Tip: A pro cleaning not only saves you effort — it can extend the life of your deck too.
Bonus Tips: Seasonal Deck Maintenance
Spring and Summer
Warm weather means your deck sees more use — and more exposure to pollen, sun, and moisture. Here’s how to keep it looking its best:
- Remove pollen and dust weekly to prevent buildup and discoloration
- Rinse off spills quickly, especially greasy food or drinks from cookouts
- Check for mold or algae in shaded or damp areas and spot clean as needed
- Inspect for signs of wear or raised screws before furniture goes back in place
A light, clean, or soft wash in early spring is a great way to prep your deck for the busy outdoor season.
Fall and Winter
As the weather cools and leaves start falling, it’s time to shift focus from appearance to protection. Here's what to do:
- Clear leaves regularly to prevent staining or moisture traps
- Use a plastic shovel or broom to remove snow and ice — never metal tools that can scratch the surface
- Apply anti-slip treatment or mats in high-traffic areas to stay safe during icy conditions
- Avoid rock salt — choose calcium chloride-based ice melt if needed, and rinse it off when temps rise
Tip from the field: Don’t cover your composite deck with tarps or rugs that trap moisture. Instead, let it breathe to prevent mold and mildew buildup through the winter.
FAQs About Power Washing Composite Decking
Will power washing void my warranty?
It can, depending on the manufacturer. Many composite decking brands allow pressure washing, but only under specific conditions — usually involving a PSI limit (typically under 1,500 PSI) and the use of a wide-angle nozzle.
Always check your decking brand’s care and cleaning guidelines. If you’re unsure, a professional service like SWKS Power Washing can clean it safely without risking your warranty.
Can I use bleach on composite decking?
No — bleach is too harsh for composite materials. It can cause discoloration, surface breakdown, and long-term damage, especially with repeated use. Bleach may also corrode fasteners or surrounding landscaping.
Stick with deck-safe, biodegradable cleaners like OxiClean™, Simple Green®, or specialized composite cleaning products. These remove mold and stains effectively without harming your deck.
How often should I power wash composite?
Once or twice a year is usually enough. Over-cleaning can wear down the surface over time, even if done correctly.
We recommend:
- Once in the spring to clear winter buildup
- Once in the fall if you’ve had heavy use or leaf debris
If your deck stays fairly clean, a soft wash or light manual cleaning may be all you need between deep cleans.
What if I’ve already damaged my deck?
If you've used too much pressure or the wrong nozzle and left streaks, gouges, or etching behind, unfortunately, composite boards can’t be sanded or refinished like wood.
Here’s what you can do:
- Try blending the damage with gentle scrubbing and cleaning
- For deep damage, board replacement may be your only option
- Call a pro to assess it, sometimes what looks bad can still be cleaned up
At SWKS Power Washing, we’ve helped many homeowners recover from pressure washing mishaps. A second opinion could save you from replacing boards unnecessarily.
Final Verdict: Yes, With the Right Method
Yes, you can power wash composite decking, but only if you do it the right way. With the proper pressure settings, equipment, and technique, power washing is a safe and effective way to remove dirt, mildew, algae, and built-up grime without damaging the surface.
The key is to stay between 1,000 and 1,500 PSI, use a 40-degree fan tip nozzle, and always spray at least 12 inches away from the surface while following the grain of the boards. Harsh chemicals like bleach should always be avoided, as they can weaken the material and strip away its finish.
If you're taking the DIY route, just make sure to read your decking manufacturer’s cleaning guidelines first, take your time, and test in an inconspicuous area. And if you're unsure or simply want the peace of mind that it’s being done right, hiring a professional is always a smart move.
At SWKS Power Washing, we’ve helped countless homeowners across Southwest Kansas safely restore the look of their composite decks. Whether you need a one-time deep clean or seasonal maintenance, we’re here to help you protect your investment and enjoy a cleaner, longer-lasting outdoor space.
CONNECT WITH YOUR LOCAL POWER WASHING SPECIALIST TODAY!