Short answer: concrete 2,500 to 3,000 PSI, brick 1,000 to 2,000, stucco under 1,500, wood 500 to 1,200, painted siding 500 to 800, vinyl under 500. PSI at the trigger is not PSI at the wall. Nozzle angle and standoff distance move it more than the machine does. Every figure below assumes a fan tip at least 12 inches out.
Concrete flatwork: 2,500 to 3,000 PSI, 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 plan on re-sanding the joints afterward. Hard-fired modern brick with sound mortar: 1,500 to 2,000, 25 degrees, 12 inches out. Brick with soft lime mortar, generally anything pre-1930: 500 to 800, and lean on chemistry instead. Traditional three-coat cement stucco in good condition: 1,000 to 1,500, 25 to 40 degrees, 18 inches. EIFS synthetic stucco: under 500, no exceptions. Cedar siding and softwood decking: 500 to 600, 40 degrees, 12 inches, moving with the grain. Dense hardwood decking such as ipe: 1,000 to 1,200. Painted wood or fiber cement with sound paint: 500 to 800, 40 degrees, 18 inches. Vinyl siding: under 500, worked top-down and angled downward. That last one surprises people, and it causes the most expensive mistakes on this list.
A 4,000 PSI rating is pump output at the trigger, not what lands on the wall. A flat fan spreads as it travels, and the force along the strike line drops in proportion to how wide that fan has gotten. Run it: a 25 degree tip throws a fan roughly 0.44 times the standoff distance, so about 2.7 inches wide at 6 inches out and 10.6 inches wide at 24 inches. Same machine, same trigger, roughly a quarter of the force per inch. Distance is the real dial, not the unloader. GPM matters more than PSI once the soil is loosened, because volume carries it away. Cleaning units, PSI times GPM, measure throughput: a 3,000 PSI gas unit at 4 GPM makes 12,000; a 1,800 PSI electric at 1.3 GPM makes 2,340. Tip colors are standard: red 0 degrees, yellow 15, green 25, white 40, black 65 for soap. Red stays in the box.
Every limit above traces to a specific way the surface fails. Vinyl siding is a rainscreen, not a waterproof skin. Panels hang loose and overlap, so a wand aimed upward under a lap drives water behind the wall where it has no path out. The siding looks perfect. The sheathing does not, eighteen months later. Brick almost never fails at the face; it fails at the joints, and eroded mortar means repointing at roughly $8 to $15 per square foot. Stucco fails by opening hairline cracks into a route to the paper and lath behind it. Softwood raises its grain, called furring, and a furred cedar deck dries rough, holds dirt worse than before, and only comes back with sanding. Painted siding is not cleaned by high pressure, it is stripped. Concrete fails cosmetically: a tight tip held too close scours the cement paste away in stripes, and those stripes are permanent.
Pressure removes what is stuck on. Chemistry removes what is growing, and on siding nearly everything is growing: algae, mildew, lichen. A soft wash puts down a dilute sodium hypochlorite solution, commonly around 0.5 to 1 percent at the surface with a surfactant so it clings, lets it dwell 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. No pressure required, so none is used. That is why Reflekt house washing is priced as soft wash at $0.18 per square foot, while pressure washing at $0.20 per square foot is aimed at flatwork, where pressure genuinely is the tool. Pre-wet landscaping and rinse it again after, keep hypochlorite off anodized and painted aluminum frames, and never mix it with an acidic cleaner.
Three cases where the honest answer costs us money. Small flatwork: at $0.20 per square foot, a 200 square foot patio prices out around $40, below any real minimum, and a big-box rental at roughly $40 to $90 a day or a $200 electric machine handles it fine. Rent the machine. Siding with failing paint: if paint chalks onto your palm or is lifting at the edges, washing it removes paint and delays the job you actually need. Call a painter first. And damage that no wash reverses: wand stripes in concrete, furred wood, spalled freeze-thaw concrete, tire plasticizer stains, and deeply carbonated gray concrete do not come back with more pressure. Those are grinding, resurfacing, sanding, or replacement conversations. Anyone quoting a wash to fix them either has not looked closely or is counting on you not noticing until the check clears.
The practical washing window in the Treasure Valley runs mid-March through late October. The hard rule is the overnight low. If it drops below freezing tonight, do not wash concrete today, because water driven into the pores expands and accelerates the exact surface spalling you were trying to clean up. Below roughly 40 degrees ambient, hypochlorite works slowly and rinse water sheets into ice on walkways. July and August bring the reverse problem: a south-facing wall sitting at 95 degrees flashes a soft wash mix dry in under two minutes and leaves streaks, so work the shaded elevation, start early, and keep the surface wet. Valley-specific loads are real, too. Pressurized canal irrigation runs roughly mid-April to mid-October and lays silt plus 10 to 13 grain hard water onto lower siding and north-facing concrete, and August wildfire smoke leaves a fine ash film on everything.
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Under 500 PSI, applied top-down and angled downward, is the safe working range. Vinyl itself can survive more, but the wall behind it cannot. Panels overlap loosely by design and are not sealed, so any upward spray under a lap pushes water into the sheathing. The damage shows up as soft sheathing or interior mold a year or more later, long after the siding looked clean. Soft wash instead.
That is wand striping, and it means the tip was too tight or held too close, so it scoured the cement paste off in the path of the jet. The stripes are not dirt patterns; they are eroded concrete, and no additional washing evens them out. Prevention is a surface cleaner, which spins two nozzles under a shroud at a fixed height. The only real fix afterward is grinding or resurfacing.
Hard-fired modern brick with sound mortar takes 1,500 to 2,000 PSI at a 25 degree tip from about 12 inches. The risk is never the brick face, it is the joints. Soft lime mortar, typical of pre-1930 masonry, erodes quickly, and repointing runs roughly $8 to $15 per square foot. Test a low, hidden square foot first. If sand comes off the joint on a wet finger, drop to chemistry and rinse pressure.
Cedar, pine, and other softwoods want 500 to 600 PSI with a 40 degree tip held about 12 inches out, moving along the grain in overlapping passes. Dense hardwood like ipe tolerates 1,000 to 1,200. Never use a turbo or zero degree tip on wood. Too much pressure raises the grain, which is called furring, and a furred deck dries rough, grabs dirt faster, and requires sanding before it can be stained.
Tap it with a knuckle. Traditional three-coat cement stucco sounds solid and dense; EIFS synthetic stucco is foam-backed and sounds hollow. Check window and door trim too, since EIFS trim bands are usually shaped foam. Traditional stucco in sound condition handles 1,000 to 1,500 PSI at 25 to 40 degrees from 18 inches. EIFS gets soft wash under 500 PSI only, because a breach in that coating routes water straight into the foam.
Usually yes for exterior flatwork. The controlling factor is the overnight low, not the daytime high. Water forced into concrete pores that then freezes drives spalling, so a January wash can leave the slab worse than the algae did. Cleaning solutions also slow down badly under about 40 degrees, and rinse runoff turns walkways into a liability. Mid-March through late October is the realistic season here.
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