You can pressure wash wood. That’s the short answer. But the long answer is far more useful — yes, you can, but only if you do it properly. Blast a wooden surface with a 3000 PSI pressure washer and you’ll likely turn your beautiful garden decking into a splintered mess. Pressure washing wood is less about power and more about precision. The type of wood matters, the condition it’s in matters, and most of all, the pressure setting you choose makes all the difference.
If you’ve got timber features around your London home — a patio deck in Walthamstow, a shed in Dulwich, or maybe a vintage bench in Islington — you need to be careful. Pressure washers can work wonders, but they’re not magic. Use too much force and you’ll leave behind deep lines, fuzzy fibres, or even cracks that weren’t there before. Use too little and, well, you’re basically just giving the mould a light rinse.
So, where’s the sweet spot? Somewhere between 500 and 1500 PSI for softwoods, maybe a bit higher for hardwoods — but never leap straight into 3000 territory. And that’s just one piece of the puzzle. Weather conditions, nozzle choice, technique, and the wood type itself all play a role. Let’s break it all down so your next clean-up doesn’t become a cover-up job.
The Basics: What’s PSI, and Why Should You Care?
Understanding Pressure Settings
PSI stands for Pounds per Square Inch, and it measures the force of water coming out of your pressure washer. The higher the PSI, the more powerful the blast. Think of it like this:
- 1500 PSI: Enough to clean softwood, like pine, without shredding it to bits. Ideal for delicate jobs or older timber that’s already been weathered.
- 3000 PSI: A brute. More suited for concrete, brick, or stubborn grime on very durable materials — not your nan’s wooden garden bench.
Wood doesn’t love high-pressure anything. It’s porous, soft (depending on the species), and it moves with temperature and moisture. That means blasting it with 3000 PSI is like trying to sand a violin with an angle grinder. The result won’t be pretty.
For pressure washing wood, your safest bet is starting low and working your way up. A PSI of 500 to 1200 is usually the sweet zone for cleaning without causing damage. You can always test on a small, hidden spot first — just to be sure.
The Role of Nozzles
Don’t ignore the nozzle angle. A 25- to 40-degree nozzle is usually your best friend for wooden surfaces. That wider spray pattern spreads out the pressure, reducing the risk of gouging or cutting into the surface.
Common Outdoor Wooden Surfaces in London Homes
Decks, Fences, Sheds — Each Needs a Slightly Different Approach
Walk through any London street, and you’ll spot wooden surfaces in nearly every back garden or courtyard. Some are new and pristine, others are older and wearing a coat of algae. Each one deserves its own game plan.
Garden Decking
Decks are usually made from softwood like pine or spruce, and sometimes hardwoods like oak or teak. Softwoods are more vulnerable to damage, so aim for 500 to 800 PSI. Stick with a wide nozzle and keep the wand at least 12 inches away from the surface.
Pro tip: Always wash with the grain of the wood. Going against it raises fibres and makes the surface rough.
Fences
Fences take a beating in London’s climate. They’re often made of treated pine or cedar. You can go slightly higher on the PSI — up to 1200 — but again, test a small patch first. Since fences are vertical, work from bottom to top to avoid streaking.
Watch out: Old, dry fences crack more easily, especially during hot weather. Keep an eye out for brittle patches.
Garden Sheds
Most wooden sheds are treated but still quite delicate. PSI under 1000 is safest. Focus on removing moss, dirt, and grime rather than peeling off paint — unless you want to strip the surface for repainting.
Tip: Use a detergent suitable for wood to loosen grime first. Let it soak for 5–10 minutes before rinsing.
Weather Matters More Than You Think
Why Sunny Days Aren’t Always Best
London’s weather can be unpredictable, but it still plays a big role in how your wood responds to pressure washing. Wood is like a sponge — it expands, contracts, dries out, or swells depending on the weather.
Hot, Dry Days
Wood dries quickly, which sounds good in theory. But rapid drying can cause cracking, especially if you’ve soaked the wood first with a pressure washer. Avoid peak heat hours. Aim for early morning or late afternoon sessions.
Cold or Damp Conditions
In winter or wet spells, wood holds more moisture and may already be swollen. Hitting it with more water under pressure can drive moisture deep into the grain, inviting rot or mould down the line.
Best conditions? Mild, overcast days with light humidity. Basically, the classic British grey sky.
Windy Days
Not ideal. The wind dries the wood unevenly and makes it harder to control the spray pattern. You also don’t want to blow grime and detergent all over your windows or your neighbour’s garden gnomes.
Pro Tips To Keep Your Timber Safe
Avoid Damage With These Simple Tricks
Pressure washing wood is about control, not power. Here’s how to clean smart:
Test First
Find a discreet area. Test your settings and technique there. If the grain raises or the wood splinters, drop the PSI and widen the nozzle angle.
Keep Moving
Never hold the wand in one spot. Constant movement avoids digging into the surface. Long, sweeping strokes along the grain work best.
Use The Right Detergent
Pressure washers alone may not get the job done. A wood-friendly detergent can break down grime so you don’t have to rely on raw pressure. Always rinse thoroughly.
Watch The Distance
Hold the nozzle about 12 to 18 inches away from the wood. Too close, and you risk carving lines into the surface. Too far, and the pressure drops to nothing.
Let It Dry Properly
After washing, let the wood dry fully — usually 24 to 48 hours. Then, if needed, sand any raised fibres lightly with fine-grit paper and reseal the surface with a wood oil or outdoor sealant.
Protect Nearby Surfaces
Use plastic sheeting or old towels to cover glass, brick, or delicate plants. Pressure washers don’t discriminate — they’ll blast anything in their path.
Should You Even Bother? Or Just Use a Hose?
Sometimes Old-School Is Better
If your wooden surface is only slightly dirty or covered in dust and pollen, a regular hose, brush, and a bucket of warm soapy water might do the trick. Pressure washing makes sense when you’ve got serious build-up — algae, mildew, years of grime — but don’t make it your go-to every time.
Every wash, no matter how gentle, wears down the wood just a little. Use pressure washers sparingly, maybe once or twice a year. In between, keep things tidy with a soft broom and quick hose-downs.
The Final Word
Pressure washing wooden surfaces is one of those tasks that seems easy — until you gouge a groove through your expensive decking or blast a fence panel into your neighbour’s compost heap. The trick lies in balance. Use the right PSI, mind the weather, test first, and always work with the grain. Done right, it’s one of the fastest ways to make tired old wood look like new again.
If you’re in London and thinking about freshening up your garden or patio, take your time. A bit of planning goes a long way. And remember — pressure washing isn’t just about pressure. It’s about care, patience, and knowing your wood.