A pressure washer is the only garden tool that can cost you a siding replacement in fifteen seconds. This is the list of things to leave alone, with why each one fails and what to use instead. It is worth reading before the first use rather than after.
1. Roof shingles
Why: asphalt shingles are protected by a bonded layer of mineral granules. Pressure strips them, permanently, which shortens the roof’s life. It also drives water up under the shingles into the roof structure.
Instead: a no-rinse outdoor treatment applied from the ground, left to work over weeks. For a roof this is not a compromise, it is the correct method.
2. Electrical panels, meters, service heads and outdoor outlets
Why: water and mains electricity. Also, you do not own the service head.
Instead: cover them, or keep well clear and wipe by hand with the power off.
3. Air conditioning condenser fins
Why: the fins are thin aluminum and they bend. Bent fins restrict airflow and cost efficiency permanently.
Instead: a garden hose at low pressure, from inside outward, or a purpose coil cleaner.
4. Anything that might be lead paint
Why: if the building predates 1978, assume lead until tested. Pressure washing aerosolizes it and spreads chips and dust across soil where children play.
Instead: test first, and if positive, treat it as a containment job with proper procedures — not a weekend task. See pressure washing before painting.
5. Old or crumbling mortar
Why: aged lime mortar and deteriorated pointing wash out. Once the joints are open, water gets into the wall.
Instead: a soft brush and a cleaner, at low pressure. On a historic building, take advice before cleaning anything.
6. Windows, skylights and anything double-glazed, at close range
Why: the glass is fine; the seals are not. Driving water past a failing seal gets it into the unit, where it fogs and stays. Skylights are worse because the water goes inside.
Instead: a wide tip at distance, or hand-wash. Angle across seals, never into them.
7. Painted or stained wood you want to keep
Why: paint lifts at every edge, and once a flake starts the jet takes the rest.
Instead: soft wash with a cleaner and a brush. If you want the paint off, that is a scraping job.
8. Composite decking above its stated pressure
Why: it fuzzes the surface, which then holds dirt worse than before, and the damage is not sandable out the way timber’s is. Most manufacturers publish a maximum pressure.
Instead: find your manufacturer’s figure and stay under it, or use a brush attachment — the deck method.
9. Vinyl siding, sprayed upward
Why: siding is lapped boards over an air gap. Upward spray goes behind it into the wall cavity and stays, and the resulting rot costs vastly more than dirty siding.
Instead: angle downward or straight on, with detergent doing the cleaning — the siding method.
10. Engine bays and anything with electrical connectors
Why: water forced into a connector causes faults that appear days later and are miserable to trace.
Instead: low-pressure spray and a brush — is it safe to pressure wash a car.
11. People, pets, and yourself
Why: a pressure washer jet will cut skin, and the resulting injuries inject debris and bacteria under the skin. They are treated as serious wounds, not grazes. Never point it at anyone, never test it on your hand, and never let a child hold the gun.
Instead: nobody needs convincing of this one. Safety basics are in pressure washer safety for beginners.
The borderline cases
Brick. Modern brick is fine; soft old brick and its mortar are not. Test an inconspicuous area.
Natural stone paving. Usually fine at low pressure, and limestone and some sandstones react to acidic cleaners. Check the supplier’s care guide.
Stucco and render. Sound render takes a wide tip at distance; cracked or hollow render will let water in behind it.
Gutters. The outside and the trough, yes, from the ground. Never spraying up into the eaves — gutter attachments.
The one habit that prevents most of this
Test an inconspicuous area first, with the widest tip, from further away than you think you need, and move in. Behind a downpipe, under a step, at the back of the deck. Thirty seconds, every new surface.
