Pressure washing guide
How to pressure wash decking safely
Decking becomes slippery and unsightly through moss and algae build-up but is vulnerable to damage from incorrect pressure washing. Used carefully at low pressure along the grain, a pressure washer can restore decking effectively without splintering or warping the wood.
Decking surfaces in London develop green algae and moss rapidly due to the damp climate and the shaded conditions of many London gardens. This not only looks unpleasant but makes the surface dangerously slippery when wet. Pressure washing can restore decking effectively but it requires more care than cleaning concrete or paving because wood is soft, porous and directional. The wrong technique causes splintering, raised grain, waterlogging and premature deterioration.
500 to 1,200
PSI maximum recommended for softwood decking. Hardwoods can handle up to 1,500 PSI.
With the grain
always wash along the direction of the wood grain, never across it, to avoid splintering and raising fibres
40 degree
wide fan nozzle only for decking. Never use a rotary pencil jet or 0-degree nozzle on any wood surface
Check the condition of your decking before starting
Before pressure washing, inspect the decking carefully. Boards with visible rot, dark patches of softened wood, crumbling or cracked sections should not be pressure washed as the force will accelerate deterioration significantly. These boards need replacing first. Decking that has been treated with a peeling or flaking sealant also needs that old coating removed before cleaning, otherwise the pressure washer will simply strip it unevenly.
Step by stepHow to pressure wash decking correctly
Step 1: Clear and sweep the decking
Remove all furniture and items. Sweep away loose debris, leaves and grit. Use a narrow brush to clear debris from between decking boards.
Step 2: Pre-treat with a wood cleaner
For heavily soiled or green decking, apply a wood-specific or biodegradable deck cleaner. Leave for 5 to 10 minutes. Do not let it dry on the surface as this can cause marks.
Step 3: Set the pressure washer to low
Set to the lowest effective pressure. Test on an inconspicuous area first. For softwood, start at 500 PSI and increase only if needed. Use the 40-degree wide fan nozzle throughout. Never use a rotary or pencil jet nozzle on wood.
Step 4: Wash along the grain, keep moving
Always move the nozzle parallel to the wood grain. Maintain a distance of 30 to 40 cm from the surface. Keep moving continuously — never pause in one spot. Work in long, even strokes along each board.
Step 5: Rinse thoroughly
Rinse the entire decking surface to remove any cleaning product residue. Sweep away excess water to prevent pooling and accelerated reabsorption into the wood.
Step 6: Allow to dry before treating
Allow the decking to dry for at least 24 to 48 hours before applying any oil, stain or sealant treatment. Wet wood will not absorb treatment properly. A moisture meter reading below 15% is the professional standard before sealing.
Different approach for composite decking
Composite decking is more resistant to pressure washing than natural timber but still requires the wide fan nozzle at low to medium pressure. The main risk with composite decking is chipping or cracking edges under concentrated pressure, particularly at the board ends. Keep the nozzle well back from board edges and never exceed medium pressure on composite materials. Composite decking does not typically require oiling or sealing after cleaning.
Professional pressure washing London
Professional decking cleaning across London
Cloud Nine cleans timber and composite decking across London using low pressure settings and correct technique that protects the surface and produces lasting results. Contact us for a free quote.
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Pressure washing help and guidance
Everything you need to know about pressure washing for London homes and businesses, from surface types to costs and what to expect from a professional clean.
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