Surface

Safe pressure by surface

Siding and walls

Surface	Method	Pressure	Avoid
Vinyl Siding	Soft wash	Low pressure, typically under 500 PSI at the wall, with the cleaning solution doing the work	High pressure aimed up under the panel laps, and hot water on dark-colored vinyl, which can warp.
Brick	Low-pressure wash	Usually 500-1,500 PSI with a wide fan tip, held well back from the mortar	Zero-degree tips and close-range blasting that erode mortar joints, and strong acids on brick that hasn't been pre-wet.
Stucco	Soft wash	Soft wash only, typically under 500 PSI	High pressure, which can etch the texture, blow out patches and push water behind the wall.
Wood Siding	Soft wash	Soft wash, typically under 500 PSI; up to about 1,000 PSI with a wide tip for bare wood prep	High pressure that raises fibers, gouges the wood or strips sound paint unevenly.
Fiber Cement Siding	Soft wash	Soft wash, typically under 500 PSI; most manufacturers advise against high-pressure washing	High pressure and close-range spraying, which can damage the finish and void the finish warranty.
Stone & Stone Veneer	Low-pressure wash	Soft wash for veneer; up to about 1,500 PSI on solid natural stone, depending on the stone	High pressure on manufactured veneer, and acidic cleaners on limestone, marble and other calcium-based stone.
Aluminum Siding	Soft wash	Soft wash, typically under 500 PSI	High pressure, which dents thin panels and strips chalky paint unevenly.
EIFS (Synthetic Stucco)	Soft wash	Soft wash only, typically under 300 PSI	Any high pressure, which can tear the finish coat or drive water into the wall system.
Log Homes	Low-pressure wash	Low pressure with a wide tip; higher pressure only as part of stripping old finish before refinishing	High pressure that furs the wood and forces water deep into checks in the logs.

Roofs

Surface	Method	Pressure	Avoid
Asphalt Shingle Roofs	Soft wash (no pressure)	No pressure washing; the solution is applied at very low pressure and rinsed gently	Pressure washing, which strips granules and shortens the roof's life, and walking on wet, slick shingles.
Metal Roofs	Soft wash	Soft wash, typically under 500 PSI	High pressure at the seams and fasteners, and abrasive or strongly acidic cleaners that dull the paint.
Tile Roofs	Soft wash	Soft wash; low pressure only on sound concrete tile	High pressure, which erodes the surface of concrete tile, and stepping on the middle of tiles.
Cedar Shake Roofs	Soft wash	Soft wash only	High pressure, which erodes and splits the wood and shortens the roof's life.

Concrete, stone and flatwork

Surface	Method	Pressure	Avoid
Concrete	Pressure wash with a surface cleaner	Usually 2,500-3,500 PSI with a rotary surface cleaner for even results	Holding a narrow tip close to the surface, which etches lines into the cream layer of the concrete.
Pavers	Pressure wash with a surface cleaner	Usually 1,500-3,000 PSI with a surface cleaner, adjusted to keep joint sand in place where possible	A narrow tip aimed into the joints, which blows out sand and can loosen pavers.
Stamped Concrete	Moderate-pressure wash	Usually 1,500-2,500 PSI, kept even so the sealer isn't stripped in patches	High pressure that strips sealer unevenly or wears off color release on the surface.
Flagstone	Low-to-moderate pressure wash	Usually 1,000-2,000 PSI, depending on the stone	High pressure on soft or layered stone, and acids on limestone.
Travertine	Low-pressure wash	Usually under 1,500 PSI with a wide tip	Acidic cleaners (including vinegar) and high pressure, which pit the stone and open its pores.
Asphalt	Low-to-moderate pressure wash	Usually 1,500-2,500 PSI; hot water helps with oil	High pressure and harsh solvents that loosen the aggregate and break down the binder.
Exposed Aggregate	Moderate-pressure wash	Usually 1,500-2,500 PSI with a surface cleaner	High pressure at edges and cracks, which can pop out aggregate.

Decks and fences

Surface	Method	Pressure	Avoid
Pressure-Treated Wood	Low-pressure wash	Usually 500-1,200 PSI with a wide fan tip	High pressure and narrow tips, which leave furry, gouged boards and lap marks.
Cedar	Low-pressure wash	Usually 500-800 PSI; cedar is soft and marks easily	High pressure, which gouges the soft wood and raises the grain.
Composite Decking	Low-pressure wash	Low pressure, often under 1,500 PSI with a wide fan tip, held well back; check your decking brand's care guide	High pressure and narrow tips, which can scar the surface and may void the warranty.
Vinyl Fencing	Soft wash	Soft wash, typically under 1,000 PSI	High pressure that can crack older, brittle vinyl and loosen rails.

PSI vs. GPM

PSI (pounds per square inch) is how hard the water hits. GPM (gallons per minute) is how much water flows, which is what carries dirt away and makes the job faster. Professionals often multiply the two into "cleaning units": a 3,000 PSI, 4 GPM machine cleans much faster than a 3,000 PSI, 2 GPM one without hitting any harder. More PSI is not better on most surfaces; the right method is.

Nozzle tips by color

Color	Spray angle	Use
Red	0°	A pencil-thin jet. Strong enough to cut skin and gouge wood, siding and concrete. Rarely needed and best avoided.
Yellow	15°	A narrow fan for stubborn spots on hard concrete and metal. Easy to leave etched lines with.
Green	25°	The general-purpose tip for concrete, brick and outdoor furniture, held at a safe distance.
White	40°	A wide, gentle fan for siding rinse, wood, windows and vehicles.
Black	65° (soap)	A low-pressure tip that lets the machine draw and apply detergent. Used to apply cleaning solution, not to blast.

These colors are a widely used convention on consumer and pro machines, but check your own tips. Distance matters as much as the tip: moving the wand back cuts the pressure that reaches the surface.

Why soft washing exists

Roofs, vinyl, stucco, EIFS and painted surfaces can't take high pressure, and algae, mold and mildew grow back quickly if they are only blasted off the surface. Soft washing uses a cleaning solution, applied at low pressure, to kill the growth, then a gentle rinse. It cleans more thoroughly and lasts longer on these surfaces, and it's why roofing manufacturers' groups advise against pressure washing shingles.

Safety: never point a pressure washer at people, pets or your own hand or foot. A high-pressure jet can inject water under the skin, which needs emergency medical care even if the wound looks small. Wear eye protection and closed shoes, and never use a pressure washer from a ladder.

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Safe Pressure (PSI) Guide in Wisconsin