Can You Pressure Wash Decking?

Thinking about pressure washing your deck? While it’s a tempting way to quickly clean away all that built-up grime, the biggest issue with power washing is the pressure—and applying too much could damage your decking.

As someone who’s been in the deck business for years, I’ve heard it all, from customers who pressure washed their deck a little too enthusiastically to those who are hesitant to even touch a pressure washer for fear of ruining their investment.

However, there is a safe way to achieve a clean garden deck with a pressure washer, and I’ll guide you through it here. But if you’re feeling unsure, you may want to leave the pressure washing to the professionals—or clean your deck with my alternate tried-and-true method below.

Let’s get your deck looking like new!

Potential Damage from Pressure Washing

Using a pressure washer may seem like a quick and easy way to clear out all the accumulated dirt and grime; however, you need to be aware of the damage it may cause. If you have timber deck boards, a power washer’s pressure may cause splintering and damage to the timber fibres. If the timber surface already has some splintering, pressure washing will only exacerbate the issue.

You may have already heard about the problems of pressure washing a timber deck. But what about composite decking? Depending on the material, a power washer can also scar boards if the pressure is too high. If the power washing becomes too intense, it can even chip the material.

If you damage your composite deck with a vigorous power wash, it can affect the warranty. Damage caused by using high-pressure washing is generally not covered, so you would have to pay for your repairs.

If you’ve installed quality composite decking such as Trex, you should wash it semi-annually (spring and autumn are the most conducive to the weather). Trex recommends a basic cleaning with a composite deck cleaner or a combination of soap, hot water, and a soft-bristle brush.

Note: Using products containing bleach or acid will lighten the surface of Trex.

How to Pressure Wash Your Deck

Pressure washing can revive your deck, but gentleness is key. Here are my pro tips, gleaned from years in the deck industry, for a safe and effective clean.

Setting Up Your Pressure Washer

Begin by preparing your pressure washer:

Pressure Settings

Excessive pressure can result in damage. When pressure washing for the first time, be cautious and find the appropriate setting to avoid gouging or etching your deck surface:

• Wood Decking: For wooden decks, start at the lowest setting (~500 PSI), testing on a small, inconspicuous area first, and gradually increase pressure only if needed. Softwoods may only require 500-600 PSI, while hardwoods can tolerate more, potentially up to 1200 PSI.
• Composite Decking: Trex suggests using a pressure washer at 3100 PSI or less on its composite decking. Other manufacturers may recommend lower pressure or discourage pressure washing altogether. Always consult the care instructions from your decking manufacturer.

Nozzle Selection

Choose a fan tip with a 40-60 degree spread for even cleaning. This is appropriate for both wood and composite decks, providing a wide, gentle spray to wash decking effectively without damage. Additionally, I often find a brush attachment is useful for tight spaces.

Techniques for Effective Pressure Washing

When you’re ready to clean, keep these techniques in mind:

• Pre-Cleaning: Sweep away loose debris or use a blower. For most surface grime, the power of the pressurized water makes pre-treatment unnecessary. For excessive buildup, spray your deck with soap first to loosen mud or dirt and optionally scrub gently with a soft bristle brush before power rinsing.
• Distance is Key: Maintain a consistent 30-40 centimetres between the nozzle and your decking, or follow manufacturer guidelines. Gradually move closer only if needed.
• Spray Angle: Holding the nozzle at a 45-degree angle helps lift dirt with reduced impact on the surface while holding it perpendicular to the deck surface delivers optimal cleaning power. I recommend starting at 45 degrees and adjusting as needed.
• Sweeping Motion: Use a sweeping motion parallel to the wood grain. Avoid lingering in one spot, which can cause uneven cleaning and streaks.
• Clean From High to Low: Start pressure washing from the house outward, working your way down from railings and posts to the decking. This prevents dirty runoff from soiling cleaned areas.

Cleaning Hard-to-Reach Areas and Tough Stains

Here’s how to tackle tricky spots:

• Corners and Edges: Consider using a brush attachment to gently scrub tight spaces, keeping the pressure low. I advise avoiding pointed (or 0-degree) nozzle attachments. These tips concentrate all the water pressure into a single, highly focused stream, which can easily gouge or etch decking.
• Stubborn Stains: For mould, mildew, or heavily stained areas, apply a cleaning product approved for your decking material (or try a mixture of warm water and dish soap). Pre-treat tough stains, allowing them to sit for 10-15 minutes or according to the instructions, and scrub with a soft bristle brush before rinsing.

Post-Washing Care and Maintenance

Once you’ve finished, don’t forget these important aspects:

• Thorough Rinse: Rinse the deck thoroughly to remove any detergent or debris. This prevents residue buildup that attracts dirt and mildew.
• Drying Time: Allow the deck to dry completely for 48 hours before applying any stain or sealer. Moisture trapped under a sealant can lead to rot!

Following these steps and prioritizing a gentle yet effective cleaning approach, you can successfully pressure wash your deck for a refreshed and rejuvenated outdoor space.

Cleaning Without A Power Washer

The safest route for cleaning your deck is soap and water. For basic deck cleaning, you’ll need:

• A broom
• A garden hose
• A bristle brush
• A biodegradable deck-cleaning solution (dish soap can work fine); avoid bleach and acid solutions unless you’ve tested them on a small area not highly visible

Here is a simple step-by-step process for cleaning without a power washer:

1. Remove furniture and any other objects from the deck boards.
2. Sweep off any leaves or other debris from your deck.
3. Test your cleaner on a small area to ensure no staining.
4. Clean with water, a cleaning solution, and a bristle brush.
5. Scrub the entire deck.
6. Rinse off with a hose. Be sure it’s completely rinsed so it doesn’t leave a film.
7. Let the deck completely dry before moving furniture and décor back onto the deck.

Cleaning by Situation: Not every clean-up situation is the same. Trex offers the following tips for cleaning your composite deck, depending on your particular challenge.

For Dirt and Debris: The affected area should be sprayed off with a hose to remove surface debris. Use warm, soapy water and a soft-bristle brush to remove soil and debris from the embossing pattern.

Tannin due to Debris: Remove all debris from the deck using a hose or broom. Once the deck surface is dry, apply a “deck brightener” as directed by the manufacturer. Deck brighteners contain oxalic acid, which will remove tannins.

Chalk Lines: High-permanence chalk lines may discolour the surface. Use only Irwin Strait-Line® Dust-Off Marking Chalk (purple), available at www.Irwin.com.

Oil and Grease: Remove all food spills as soon as possible. The surface must be cleaned within seven days to maintain the stain warranty. To remove, spray off with a hose and use warm, soapy water and a soft-bristle brush to remove spills from the embossing pattern.

Mould and Mildew: If debris, such as pollen and soil, remains on the deck surface, mould can feed on the biofilm. To remove the food source and mould, it is recommended to use a hose and warm, soapy water with a soft bristle brush.

If your deck has reached the point of no return—it’s beyond stripping, sanding, re-staining, and repairing—make plans for a new deck. To protect your deck in all seasons, be sure to use flashing tape such as Trex Protect. With its superior waterproofing power and your deck cleaning skills, you can enjoy an outdoor living space for years to come!