Pressure washing: prices by surface, when soft-washing wins, and 4 things never to spray

Pressure washing uses high water pressure (1500-4000 PSI) to physically blast off dirt. Soft washing uses low pressure (under 500 PSI) plus chemical detergent (typically sodium hypochlorite + surfactant) to chemically dissolve organic growth. The right choice depends entirely on the surface: (1) Concrete driveway/patio — pressure wash, 2500-3500 PSI, 25° tip. (2) Vinyl siding — soft wash, never above 1500 PSI; the chemistry does the work. (3) Wood deck — pressure wash, 1200-1500 PSI maximum, 40° tip; higher pressure damages the wood fibers. (4) Roof shingles — ALWAYS soft wash; pressure washing strips the granules and voids the warranty. (5) Brick — pressure wash exterior up to 1500 PSI, but never blast directly into mortar joints; old mortar can be eroded.

A pressure washer's PSI rating is the maximum, not the operating pressure — distance from surface and tip angle do most of the regulation. Tips: 0° (red, the "blast" tip) — never use; will damage anything. 15° (yellow) — concrete, brick, stripping paint. 25° (green) — most general washing including driveways, patios, fence cleaning. 40° (white) — vinyl siding, painted surfaces, decks. Soap tip (black, 65°) — applies detergent at low pressure. Distance matters more than PSI: a 3000 PSI machine held 18" away delivers about the same force as a 1500 PSI machine held 8" away. Pros adjust by stepping closer/farther, not by changing PSI.

Asphalt shingle roofs collect black streaks (gloeocapsa magma — a cyanobacteria) over time. The temptation: blast it off with pressure. The result: shingle granules fly off, the roof loses 5-10 years of life, and the manufacturer warranty is voided. The right method: soft wash with sodium hypochlorite (~3-6% concentration) + surfactant + water, applied with a low-pressure pump and 12V-driven nozzle. The chemistry kills the algae and dissolves the staining; rinse with garden-hose pressure. Cost: $300-$700 for a typical 2,000 sq ft roof. Re-treatment lifespan: 5-7 years. The ARMA (Asphalt Roofing Manufacturers Association) explicitly endorses soft washing and warns against pressure washing.

Same principle as roofs: dirt and mildew on vinyl/aluminum/painted-wood siding need detergent + low pressure. House washes use a similar SH+surfactant solution applied at 200-500 PSI, then dwell 5-10 minutes, then rinse with garden-hose pressure. High-pressure washing of vinyl can: (1) drive water behind the siding and into the wall cavity (mold risk), (2) crack older brittle vinyl, (3) strip paint off wood/aluminum. Cost for whole-house wash: $250-$650 for typical 2-story (~2000 sq ft of siding); $500-$1200 for larger or 3-story. Add $100-$200 if heavy mildew growth requires extra dwell time.

Concrete is the one surface where pressure washing shines. Use 2500-3500 PSI with a 25° tip or — much faster — a surface cleaner (the "spinning" attachment). Surface cleaners cover 2-3x the area per minute and leave even, streak-free results. Cost: $0.20-$0.50 per square foot for plain concrete; $0.50-$1.00/sq ft for stamped or stained concrete (requires more care). Add a degreaser for oil-stained driveways ($30-$80 in product). Sealing after cleaning: optional but extends clean appearance to 18-24 months vs 6-12 months unsealed. Sealer adds $0.50-$1.50/sq ft.

(1) Roof shingles — soft wash only. (2) Windows — high pressure can crack the seal between panes; use a separate window-cleaning service or hand-wash. (3) Electric meters, AC condensers, and outdoor outlets — water + electricity = bad day. Cover or carefully avoid. (4) Old or unsealed wood (especially Douglas fir or cedar with weather damage) — high-pressure water raises the grain and causes splintering. Use a deck-stripping chemical first, then low-pressure rinse.