Safe Pressure Ranges by Surface: Concrete, Brick, Vinyl, Stucco, Wood, and Painted Siding

The safe range for every surface, in one pass

Concrete flatwork, uncolored and sound: 2,500 to 3,000 PSI with a 15 or 25 degree tip, or better, a surface cleaner. Colored, stamped, or sealed concrete: 1,200 to 1,500 at 25 degrees. Pavers: 1,500 maximum, and budget to re-sand the joints after. Hard-fired modern brick with sound mortar: 1,500 to 2,000, 25 degrees, 12 inches out. Soft lime mortar, generally anything laid before 1930: the National Park Service caps water washing of historic masonry near 100 PSI, and that is the right instinct. Traditional three-coat cement stucco: 1,000 to 1,500, 25 to 40 degrees, 18 inches. EIFS synthetic stucco: under 500, no exceptions. Cedar and softwood decking: 500 to 600 at 40 degrees, 12 inches, moving with the grain. Ipe and dense hardwood: 1,000 to 1,200. Painted wood or fiber cement with sound paint: 500 to 800 at 40 degrees from 18 inches, and James Hardie's own guidance is under 1,500 PSI with a wide fan held well back. Vinyl siding: under 500, aimed level or downward, never up.

PSI at the trigger is the number that matters least

A 4,000 PSI rating is pump output at the trigger, not what lands on the wall. A flat fan keeps spreading as it travels, and force per inch of strike line falls as the fan widens. Run the geometry: a 25 degree tip throws a fan about 0.44 times the standoff distance, so roughly 2.7 inches wide at 6 inches out and 10.6 inches at 24 inches. Same machine, same trigger, about a quarter of the force. Distance is the dial, not the unloader. Once soil is loosened, GPM matters more than PSI, because volume is what carries it off. Cleaning units, PSI times GPM, measure real throughput: a 3,000 PSI gas unit at 4 GPM makes 12,000, while an 1,800 PSI electric at 1.3 GPM makes 2,340. Tip colors are standardized: red 0 degrees, yellow 15, green 25, white 40, black 65 for chemical. The red tip stays in the box. It does not clean faster, it injects, and an injection injury needs a hand surgeon within hours.

Every number above comes from a specific failure mode

Vinyl is a rainscreen, not a waterproof skin. Panels hang loose and overlap on purpose, so spray angled up under a lap drives water into the sheathing where it has no path out. The siding still looks perfect. The OSB behind it does not, eighteen months later. Brick almost never fails at the face, it fails at the joints, and repointing runs $8 to $15 per square foot. Stucco fails by opening hairline cracks into a route to the lath and building paper. Softwood raises its grain, called furring, and a furred cedar deck dries rough, holds dirt worse than before, and needs sanding. Painted siding is not cleaned by high pressure, it is stripped. Concrete fails cosmetically: a tight tip held close scours the cement paste away in stripes, and stripes are permanent. Test first. Knuckle-rap stucco: hollow means EIFS. Drag a wet finger down a mortar joint, and if sand comes off, drop to chemistry. Then wash one hidden square foot and read it in raking light.

On siding, chemistry cleans and pressure only rinses

Pressure removes what is stuck on. Chemistry removes what is growing, and on siding nearly everything is growing: algae, mildew, lichen. A soft wash lays down dilute sodium hypochlorite, commonly 0.5 to 1 percent at the surface, with a surfactant so it clings, dwells five to ten minutes, then rinses at garden-hose pressure or through a black 65 degree tip. The growth dies and releases on its own, so no pressure is required and none is used. Never let the mix dry on the wall, re-wet it instead. Pre-soak landscaping and rinse it again after. Keep hypochlorite off anodized and painted aluminum, and never mix it with anything acidic. That split is why Reflekt prices house washing as soft wash at $0.18 per square foot and pressure washing at $0.20 per square foot, since flatwork is where pressure genuinely is the tool. Glass is a third process again: 100 percent pure deionized water, no soap.

When not to hire this out, and what no wash will fix

Three answers here cost us money. Small flatwork: at $0.20 per square foot a 200 square foot patio prices near $40, below any real minimum, and a big-box rental at $40 to $90 a day, or a $200 electric machine you keep, handles it fine. Rent it. Siding with failing paint: if paint chalks onto your palm or lifts at the edges, washing removes paint and delays the job you actually need, which is a painter. And some damage no wash reverses. Wand stripes in concrete, furred wood, freeze-thaw spalling, tire plasticizer stains, rust bleed from shallow rebar, and deeply carbonated gray concrete do not come back with more pressure. Those are grinding, resurfacing, sanding, or replacement conversations, and concrete resurfacing alone runs roughly $3 to $7 per square foot. Anyone quoting a wash to fix them either has not looked closely or is counting on you not noticing until the check clears.

Idaho timing: temperature decides more than technique

The practical washing window in the Treasure Valley runs mid-March through late October, and the controlling number is the overnight low, not the afternoon high. If tonight drops below freezing, do not wash concrete today, because water driven into the pores expands and accelerates the exact spalling you were trying to clean up. Under about 40 degrees ambient, hypochlorite slows badly and rinse water sheets into ice on walkways. July and August flip the problem: a south-facing wall sitting at 95 degrees flashes a soft wash mix dry in under two minutes and streaks it, so start early, work the shaded elevation, and keep the surface wet. New concrete gets 28 days of cure before any pressure touches it. Valley loads are specific too. Pressurized canal irrigation runs roughly mid-April to mid-October and lays silt plus 10 to 13 grain hard water on lower siding and north-facing slabs, and August wildfire smoke leaves ash film on everything.