How to Pressure Wash Wood Decking (Step-By-Step)

As we emerge from the cold, wet winter months, many of us start turning our attention back to our timber or composite decking. During those months when we’re not outside as much, it’s fair to say our decking can take a bit of a beating from the weather, leading to a build‑up of dirt, grime and sometimes even algae.

The good news is that it often only requires a drop of domestic detergent, warm water, a stiff brush (and a touch of elbow grease!) to do the trick and have your decking looking good as new. But sometimes stubborn dirt needs something a little more powerful to remove it, which is when many homeowners reach for the pressure washer.

Before you dive straight in, though, it’s important to prepare the surface properly. When used incorrectly, a pressure washer can do far more harm to a timber deck than good. Follow these quick steps to ensure you use yours safely and effectively, and pick up a couple of handy tips to help you restore your decking (or patio!) back to its best.

To give your decking a thorough, premium clean with a pressure washer, it helps to have the right kit ready before you start. Here’s everything you’ll need:

• Specific decking cleaner
• Pressure washer (150 bar maximum)
• Spray nozzles
• Rotary surface attachment (optional)
• Stiff broom
• Waterproof clothing, such as overalls and wellies
• Goggles
• Rubber gloves
• Ear defenders
• Stainer, sealer or paint (for timber decking)
• A nearby water outlet

Before switching your pressure washer on, take a moment to get yourself and your decking ready. Pop on those waterproofs, pull on your wellies and give the area a quick once‑over. Proper prep makes all the difference to the final finish.

Reducing the amount of time you spend using the high‑pressure setting will help prevent your timber boards from becoming oversaturated and at risk of splitting. A good, thorough prep also helps to keep your final clean even across the entire decking surface.

Start by taking a stiff broom and sweeping away any loose leaves, twigs or general debris. This simple step helps your pressure washer work more effectively and avoids pushing dirt deeper into the boards.

Next, pre‑treat your decking. This is especially helpful if your boards have picked up winter grime, stubborn mud or patches of built‑up dirt. Apply a wood‑specific or composite decking cleaner and allow it to soak in for 5–10 minutes. This softens the dirt and makes the washing stage much easier (always check the manufacturer’s instructions for best results).

Once your cleaner has done its job, switch your pressure washer to a low‑pressure or steam setting. Gently remove any loosened grime, surface stains or remaining detergent. Making sure all detergent is rinsed away will help keep the decking safe underfoot, preventing slippery areas once it dries.

If you’ve followed these steps, your decking should already look fresher. You’re now ready to set up your pressure washer correctly and move on to cleaning your decking without damaging the wood or composite boards.

Before you get stuck into cleaning your decking, it’s important to set your pressure washer up correctly. Most models, no matter the brand, come with a selection of nozzles and settings designed to help control the water pressure and protect your decking. For best results, use a machine with a maximum output of 150 Bar (2175.57 PSI). Anything higher can increase the risk of damaging timber boards.

Here’s how to get your pressure washer ready:

• Choose the right nozzle: Fit a fan nozzle or rotary attachment to create either a wide, even spray pattern or a gentle circulating motion. Both of these are far kinder to decking surfaces than a narrow jet.
• Load a suitable cleaning solution: If your washer allows detergent, use a wood‑specific or composite‑safe cleaner. Always check the manufacturer’s instructions to make sure you’re using it correctly.
• Select your pressure setting: Go for a medium to high power setting depending on how dirty your decking boards are. For only lightly soiled boards, especially if you clean them yearly, a medium setting is usually ideal.

Once everything is attached and your settings are locked in, you’re good to go. Pop on your ear defenders and goggles, and move on to the next steps for safely cleaning your decking surface.

Wooden decking behaves differently from harder outdoor surfaces like paving slabs, porcelain tiles or concrete. Timber naturally expands and contracts when soaked, which makes it more vulnerable to cracking or splitting if exposed to very high‑pressure water. With the right technique, though, you can achieve a deep, professional-standard clean without causing damage.

Start by cleaning a small test area, ideally somewhere that’s out of sight. This helps you check your pressure settings and spraying distance before moving on to the more visible boards.

• Keep your distance: Hold the nozzle around 6 inches (15cm) or more from the surface of the decking. Getting too close can cause the water jet to leave marks.
• Stick to one pressure setting: Use a medium to high power setting depending on how dirty the decking is, and try not to adjust it mid‑clean. Changing settings partway through can create uneven marks.
• Choose the right spray pattern: A rotating tip or a wide fan nozzle (around 40–60°) gives a thorough, even clean across larger areas. If you don’t have a rotary attachment, a wider fan nozzle will work well.
• Follow the direction of the grain: Working with the grain helps protect the surface and leaves a more natural finish once the decking dries.
• Overlap your lines: Slightly overlapping each pass helps avoid watermarks and ensures an even look.
• Keep it moving: If possible, try to avoid pausing in one spot, as this can saturate the wood and damage the grain. Aim for a smooth, consistent motion as you work across the boards.

Once you’ve washed the entire decking surface, finish with a soft spray rinse. This clears away any loose debris and leftover detergent, helping to reduce watermarks and preventing slippery patches when the decking dries.

To finish, we recommend you cool the boards with cold water from a garden hose. This gently brings the timber back to its natural temperature. Then take a dry broom and sweep away any remaining puddles. This is particularly important in the colder months, when standing water can freeze and become hazardous.

• Goggles: Protect your eyes from any flicked‑up debris.
• Ear defenders: Pressure washers can be surprisingly loud, so protect your hearing, particularly is using for prolonged periods.
• Rubber gloves: Helpful for keeping hands warm and protected from detergents.

Treating, Varnishing and Sanding Down Your Deck

Once your decking is clean and fully dry, you may want to take the opportunity to give the boards a little extra care. Treating or sanding timber decking can help protect it from future weathering and keep it looking fresh for longer.

Before you begin, as we’ve mentioned already in this blog, make sure the boards are completely dry and free from any residual decking cleaner. This will help the treatments soak in evenly and avoid patchy finishes. Once dry, you can sand the surface lightly (if needed) and choose to paint, stain or seal the wood to protect it from mould, moisture and everyday dirt.

These aftercare steps apply only to timber decking. Composite decking doesn’t require sanding, staining or varnishing, so you can simply let it dry naturally and enjoy your freshly cleaned boards.

Staining your timber deck is a great way to improve its lifespan and reduce the maintenance required throughout the year. Match the staining product colour to your deck.

Cleaning your decking does take a little time and care, but when done properly, the results are well worth it. A proper clean will lift away dirt, algae and stubborn marks, helping your boards return to their original glory.

Pressure washing timber decking naturally comes with a few risks, after all, wood is an organic material that reacts to water and temperature changes. Starting with a small test patch is the best way to make sure you’re happy with your setup before tackling the full deck, giving you a chance to adjust the pressure or spray pattern without affecting the main surface.

By following the steps above, using the right attachments and taking a steady approach, you can safely refresh your timber or composite decking. Carrying out a thorough clean once a year can also help extend the lifespan of your boards and keep your outdoor space looking its best.