Outdoor wooden decking and paved patio areas take a constant beating from rain, sun, frost, and foot traffic. Over months of exposure, algae, moss, lichen, and surface grime build up, turning once-attractive outdoor spaces into slippery, discoloured zones. A pressure washer offers one of the fastest and most effective ways to restore these areas. In this guide, you will learn how to safely clean decking and patios using a power washer, from selecting the right equipment through to post-cleaning treatment that keeps regrowth at bay.
Why Regular Power Washing Matters for Decking and Patios
Timber decking and stone or concrete patios are porous materials that absorb moisture and organic matter over time. Left uncleaned, surface growth such as algae and moss creates a slip hazard that becomes especially dangerous in wet weather. Routine power washing addresses several key issues:
- Restores visual appeal Dirt, mildew, and algae discolour timber and paving. Power washing strips away this build-up and returns the surface to its original colour.
- Prevents long-term decay Organic growth traps moisture against the surface. On timber decking, this accelerates rot and warping. On patios, it can lead to cracked slabs and loose joints.
- Improves safety A power-washed surface removes the slippery biofilm that forms on damp wood and stone, reducing the risk of falls.
- Prepares for treatment If you plan to apply stain, sealant, or timber preservation products, the surface must be clean. Coatings applied over dirt or algae will peel within weeks.
- Saves physical effort Scrubbing an entire deck or patio by hand is exhausting and rarely achieves the same depth of clean that a pressure washer delivers in a fraction of the time.
For homeowners who want to maintain their outdoor investment, a pressure washer is the most practical tool for the job.
Essential Equipment and Safety Preparations
A typical domestic power washer with at least 110 bar of pressure is sufficient for most decking and patio cleaning tasks. Budget-friendly models are available from most DIY retailers. Look for one with an adjustable lance nozzle and consider a rotary patio cleaner attachment for larger paved areas.
Here is a checklist of what you will need:
- Pressure washer (110 bar minimum) with lance and adjustable nozzle
- Outdoor water supply with hose connection
- RCD-protected electrical socket for safe power supply
- Patio cleaner attachment for large flat surfaces (optional but recommended)
- Anti-fungal cleaning solution or brick and patio cleaner
- Stiff scrubbing brush and plastic bucket
- Protective gear: thick rubber gloves, eye protection, old clothing, and respiratory mask for acid-based cleaners
- Plastic sheeting to cover nearby plants and landscaping
Safety comes first. The water jet is powerful enough to cause serious injury. Keep children and pets away. Never point the lance at people or animals. Wear sturdy footwear as the cleaned surface will be wet and slippery. For detailed guidance on timber selection and structural considerations, read our article on designing and building garden decking.
Clear the area of all furniture, potted plants, and other objects. Sweep away loose debris. Inspect decking for loose boards or rotten sections and address these before washing, because high-pressure water can worsen existing damage. On patios, check for cracked slabs or loose mortar joints. Protect nearby vegetation with plastic sheeting if using chemical cleaners.
Step-by-Step Process for Power Washing Wooden Decking
Wooden decking requires careful handling during pressure washing because timber fibres can be damaged by excessive pressure or incorrect technique. Follow this four-step process.
Step 1: Apply an Anti-Fungal Pre-Treatment
For decking with heavy algae or lichen build-up, pre-treatment is essential. Apply an anti-fungal wash such as Everbuild Fungicidal Wash using a low-pressure garden sprayer or a stiff brush. Work the solution into the timber grooves and let it sit for 20 to 30 minutes. This dwell time breaks down the organic matter. After soaking, scrub with a stiff brush to lift the loosened grime. The green and black patches will begin to dissolve visibly.
Step 2: Set Up the Pressure Washer Correctly
Connect the high-pressure hose to the main unit and attach the lance to the gun. Connect a garden hose from your outdoor tap to the water inlet. Plug into an RCD-protected socket. Turn on the water first, then the power washer. Never run the pump without water flow. Adjust the nozzle to a wide fan spray and test on an inconspicuous area first. For more on timber materials, refer to our guide on timber as a construction material.
Step 3: Wash the Decking Surface
Hold the lance nozzle approximately six inches from the decking. Work in small sections, keeping the lance moving at all times. Do not dwell on any single spot, as concentrated pressure can erode wood fibres. Always spray with the timber grain, not against it. Continue methodically until all algae and grime are removed. Rinse thoroughly with clean water to remove dirty residue.
Step 4: Apply Decking Oil or Treatment
Cleaning is only half the job. To protect your decking and slow regrowth of algae, apply a high-quality decking oil or timber treatment. These products create a protective barrier that repels moisture. Apply according to the manufacturer’s instructions and repeat annually.
How to Clean Patio Surfaces with a Power Washer
Patio cleaning follows a similar sequence but with important differences. Stone and concrete are less prone to fibre damage, so you can use higher pressure. However, the joints between slabs are vulnerable and require special attention.
Step 1: Clean the Patio Joints
Before using the pressure washer, clean out the joints between patio slabs. Use a patio scraper, block paving brush, or cleaning hook to remove weeds, moss, and debris from the gaps. Sweep up the waste. Clearing joints prevents the washer from blasting loose debris and ensures cleaning solution penetrates the paving gaps. For ideas on using your outdoor space once it is clean, see our article on furnishing and designing outdoor living areas.
Step 2: Apply Brick and Patio Cleaner
For patios, a dedicated cleaning solution such as Everbuild 401 Brick and Patio Cleaner is highly effective. It contains muriatic acid which dissolves algae, lichen, and mineral stains. Wear thick rubber gloves, eye protection, a respiratory mask, and old clothing. The fumes are toxic. Pour the cleaner into a plastic bucket (acid reacts with metal). Scrub the solution into the surface in small sections and leave for 20 to 30 minutes. A standard fungicidal wash can be used as a milder alternative.
Step 3: Power Wash the Patio Surface
After the cleaner has worked, use the pressure washer to rinse away the loosened grime. Work in straight lines across the patio and direct waste water towards a drain. A patio cleaner attachment with rotating jets can cut cleaning time in half. Heavily soiled patios may need a second cycle. For more detail on keeping timber in top condition, see our guide on treating timber decking for long-term maintenance.
Be cautious with high pressure on older or softer paving. Too much force can chip slab edges. The acid in the cleaner is diluted during rinsing and is safe for drains and soil.
Comparing Decking Materials for Cleaning and Maintenance
Different outdoor surface materials respond differently to pressure washing. The table below compares common materials in terms of cleaning requirements, damage risk, and post-wash treatment.
| Material | Power Wash Pressure | Damage Risk | Cleaning Frequency | Post-Wash Treatment |
|---|---|---|---|---|
| Softwood timber decking | Low to medium (wide fan) | High if nozzle too close | Annually | Decking oil or timber stain |
| Hardwood timber decking | Medium (wide fan) | Moderate | Every 12-18 months | Hardwood oil or sealant |
| Composite decking | Low to medium | Low | Every 12-18 months | None required |
| Concrete patio slabs | Medium to high | Low on dense concrete | Every 1-2 years | Sealant optional |
| Stone patio (sandstone, limestone) | Low to medium | High on soft stone | Every 18-24 months | Stone sealant recommended |
| Clay brick pavers | Medium | Moderate on edges | Annually | Joint sand replenishment |
Composite decking offers a particularly low-maintenance alternative because it resists moisture absorption and does not require annual oiling. For more detail, see our comparison of composite decking materials and their long-term performance.
Post-Cleaning Maintenance to Prevent Regrowth
Even after a thorough power wash, algae and lichen will eventually return without preventive steps. The regrowth timeline depends on climate, shade, and the quality of protective coatings applied. Here are the most effective measures to keep your surfaces clean longer:
- Apply protective treatment annually Reapplying decking oil or stain each year creates a moisture barrier that deprives algae of the damp environment it needs.
- Keep the surface dry Trim overhanging vegetation to increase sunlight and airflow. Shaded, damp areas encourage organic growth.
- Sweep regularly A weekly sweep removes leaves and debris before they break down into organic matter that feeds algae.
- Re-sand patio joints Power washing washes out joint sand. Replenish with kiln-dried jointing sand to stabilise slabs and prevent weeds.
- Use a mild fungicidal wash annually A light spring application prevents the heavy build-up that requires intensive cleaning later.
Power washing your decking and patio is an investment in the longevity of your outdoor spaces. By following correct preparation, cleaning, and post-treatment steps, you can keep outdoor surfaces in excellent condition for many years. Regular maintenance is far more cost-effective than waiting until the surface is heavily degraded.