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The same power that makes pressure washing effective makes it easy to cause damage. Too much pressure or a nozzle held too close can raise the grain of a cedar deck, blow the joint sand out of interlock, erode mortar and force water behind siding and into the walls. Wastewater and detergents also have to go somewhere, and in many cities storm drains are off-limits.
This page covers which surfaces can be pressure washed, how pressure washing and soft washing differ, the damage to avoid, why roofs are a separate job, the rules on runoff and cleaning products, the lead paint question on older homes and sealing surfaces after cleaning.
Surfaces you can pressure wash: decks, patios, interlock, siding, driveways and fences
- Wood decks and fences: low pressure and a wide fan tip, moving with the grain; a wood cleaner or brightener often does more of the work than the water.
- Composite decking: follow the manufacturer's cleaning instructions, since too much pressure can mark the surface and affect the warranty.
- Interlock and paving stones: cleaned to clear moss, weeds and stains from the joints, then re-sanded, often with polymeric sand, before any sealer goes on.
- Concrete driveways, walkways and patios: they tolerate more pressure, but a rotating surface cleaner avoids the stripes a wand leaves.
- Vinyl, aluminum and fibre cement siding: usually soft washed with a cleaning solution and a gentle rinse, never with the jet aimed up under the laps.
- Brick and stone: low pressure only, after checking that the mortar joints are sound.
Pressure washing vs soft washing: choosing the right method for each surface
Pressure washing relies on the force of the water to lift dirt. It suits hard, durable surfaces such as concrete and pavers, with the pressure and nozzle matched to the material. Soft washing uses low pressure, closer to a garden hose, with a cleaning solution that loosens algae, mildew and grime so they can be rinsed off without blasting the surface.
Soft washing is the safer choice for siding, painted surfaces, stucco and weathered wood, but it depends on chemistry, so ask which product will be used, how nearby plants will be protected and how the rinse water will be managed. Either way, a good operator tests an inconspicuous spot first and adjusts before going further.
Pressure washing damage to avoid: wood fibres, mortar joints, siding seams and roofs
Moss and algae on a roof are a job for a roof cleaning company using low-pressure methods suited to the roofing, or for a roofer if shingles are damaged. It's work at height, not something to take on yourself.
- Wood: high pressure or a narrow tip tears soft wood fibres, leaving a fuzzy, furrowed surface that absorbs stain unevenly and weathers faster.
- Mortar and masonry: the jet can erode aging mortar joints and the face of soft brick, letting water into the wall.
- Siding seams: water aimed upward or from close range is driven behind siding, trim and window frames, where it can wet the sheathing and insulation.
- Interlock: sand blasted out of the joints lets pavers shift and weeds return unless the joints are re-sanded.
- Windows, vents and electrical fixtures: seals, screens, dryer and exhaust vents and outdoor outlets should never take a direct jet.
- Asphalt shingle roofs: never pressure wash them; the water strips the protective granules and can be driven under the shingles.
Pressure washing runoff, detergents and storm drain rules
Catch basins and storm drains carry water toward local creeks, rivers and lakes, which is why municipal sewer bylaws limit what can go into them. Toronto's Sewers By-law is a clear example: the City says nothing but rain and melted snow may flow into an outdoor catch basin, and that wastewater from outdoor washing must not reach one, because soaps, cleaning products and the contaminants washed off a surface break the storm sewer limits. It adds that power washing with water alone still dislodges or dissolves contaminants.
The City suggests letting wash water evaporate, redirecting it away from catch basins or containing it, disposing of it in an indoor drain or hauling it away, and sweeping driveways and sidewalks instead of hosing them. Rules differ elsewhere, so check with your municipality, and ask the contractor how runoff will be handled, which detergents they use and how lawns, gardens and nearby water will be protected.
Lead paint on older homes: have it tested before pressure washing
Pressure washing old paint strips loose flakes and sends chips and contaminated water across the yard. Health Canada says a home built before 1960 probably contains lead-based paint, and one built between 1960 and 1990 may have it on the exterior. It notes that even small amounts of lead dust are dangerous to infants and children, and suggests testing by sending paint chips to a lab or hiring a contractor with the proper x-ray equipment.
On an older house, fence or porch with peeling paint, have the paint tested before any washing or prep work. If lead is present, the job calls for a contractor who contains and collects the debris, and pressure washing is usually the wrong tool; as Health Canada advises, keep children and pregnant women away from the work area.
Sealing after pressure washing: decks, interlock and concrete
Cleaning opens up the surface, which makes it the right moment to protect it, but only once it's completely dry. Wood and concrete hold water after washing, and sealer or stain applied too soon can peel, turn cloudy or trap moisture. Follow the product's directions on drying time, temperature and rain.
- Wood decks and fences: a penetrating stain or water repellent slows greying and checking; plan to recoat when water stops beading on the surface.
- Interlock: re-sand the joints first, then apply a paver sealer if you want richer colour and fewer weeds and stains.
- Concrete: a penetrating sealer limits how much water, and de-icing salt, the surface soaks up over the winter.
- Composite decking: usually needs no sealer; check the manufacturer's care guide.
Pressure Washing: frequently asked questions
Can I pressure wash my roof?
No. Pressure washing an asphalt shingle roof strips the protective granules and can force water under the shingles, on top of the danger of working at height. Hire a roof cleaning company that uses low-pressure methods, or a roofer if the shingles are damaged.
Is pressure washing safe for vinyl siding?
Only gently. High pressure aimed upward drives water behind the panels. Soft washing, with a cleaning solution and a low-pressure rinse, is the safer way to clean vinyl, aluminum and fibre cement siding.
Should I pressure wash my deck before staining it?
It needs cleaning before staining, but not necessarily at high pressure. A deck cleaner and a low-pressure rinse, moving with the grain, remove grime without raising the fibres. Let the wood dry fully before staining, as the stain's directions specify.
Can pressure washing water go down the storm drain?
Not in cities like Toronto, where only rain and melted snow may enter an outdoor catch basin. Check your municipality's rules, and ask the contractor how runoff will be kept out of the street drains.
When is the best time of year for pressure washing?
From late spring to early fall, when there's no risk of freezing and surfaces dry quickly. A spring wash clears winter salt and grime; a late-summer wash leaves time for a deck or pavers to dry before sealing.
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Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides