The single most common preventable damage we see on commercial properties is the aftermath of a pressure-washing crew that used the wrong technique. Blown-out mortar joints. Etched limestone. Stripped paint on cornices. Ninety percent of it comes from one mistake: someone brought a 4,000 PSI rig to a surface that needed a 300 PSI rig plus dwell time.
Pressure washing: when it's the right tool
High-pressure water (2,500–4,000 PSI at 200°F) is the right tool for concrete sidewalks, unpainted concrete masonry units, sealed asphalt, dumpster corral floors, and machinery. It works by mechanical force — physically blasting the debris off the surface. It's fast, effective, and completely inappropriate for anything softer than concrete.
Soft washing: when to switch
Soft washing runs at under 500 PSI and relies on a specialty cleaning solution — typically a low-concentration sodium hypochlorite blend for organic growth, or a specialty alkaline detergent for oil and grease — that dwells on the surface for 5–15 minutes before being rinsed off. It's the correct method for painted surfaces, siding, roofs, awnings, sensitive stone (limestone, sandstone, aged brick), and any surface where the cleaning is chemical rather than mechanical.
The vendor test
The easiest way to spot a vendor who doesn't understand the distinction: ask them what PSI they'd use on your building's stone facade. If the answer is a single number — 'three thousand should do it' — they don't understand their equipment. The correct answer is a range that depends on the substrate: 200–400 PSI for aged limestone, 500–800 for concrete masonry, 1,200–1,800 for sealed concrete. Different tools, different jobs.
