What PSI Does and Does Not Tell You
PSI is force at the tip. Flow rate is how much water carries debris away. Tip angle spreads or concentrates the force. Distance from the surface changes the delivered pressure more than the machine setting does. Damage on residential work almost never comes from a machine being too powerful — it comes from the wrong tip at the wrong distance on the wrong material.
Which Surfaces Take Pressure
Poured concrete drives and walks take pressure with a surface cleaner for an even pass. Concrete pavers tolerate pressure but joint sand will need replacing afterward. Bluestone and flagstone need low pressure or soft washing — natural cleft flakes under a tight tip. Asphalt driveways need low pressure or rinse only since high pressure scars the binder. Siding, stucco, stone facades and roof shingles should never be pressure washed — those are soft wash surfaces.
See also: Soft Washing on the Main Line · Patio & Walkway Washing
Sequence Matters on a Full Property
Working order on a typical Main Line house: protect plantings and shut windows first. Roof and gutters go first if they are in scope so runoff lands on surfaces you have not cleaned yet. Soft wash the house top down. Pressure wash hardscape last, which also rinses whatever the house wash carried down. Re-sand paver joints if pavers were cleaned.
See also: House Washing Main Line PA · Gutter Cleaning Main Line PA
By Town
Blue Bell (19422): open full-sun lots and the longest hardscape intervals in the area. Newtown Square (19073): the most hardscape per property plus the highest pool density. Wynnewood (19096): street trees over the drive mean leaf tannin staining, which needs a cleaner not more pressure. Gladwyne (19035): long sloping drives and outbuilding aprons. Conshohocken (19428): steep hillside drives and steps where the film is a genuine winter hazard. Ardmore (19003): shared drives and narrow side walks between twins. Narberth (19072): small borough lots, short runs. Paoli (19301): everything from 1890s brick walks to 2000s stamped concrete. Malvern (19355): historic borough sidewalks alongside large modern driveways. Haverford (19041): estate drives, courtyards and stone steps under heavy shade.