Soft Wash vs Pressure Wash

How Each Method Actually Works

The two methods don't just use different amounts of pressure. They clean in different ways.

Pressure washing cleans with force

A pressure washer uses pressure as the stripping force that knocks dirt loose and flow as the rinsing power that carries it away (Mi-T-M). That's ideal for hard, durable surfaces. Consumer Reports notes that concrete driveways and walks can handle a powerful cleaning, while the same stream can damage paint and nick or etch wood (Consumer Reports).

Soft washing cleans with chemistry

A soft wash puts on a cleaning solution at low pressure, gives it time to work, then rinses it off gently. The solution does two jobs. Sodium hypochlorite is an oxidizer: CDC describes chlorine oxidizing cell components and notes that hypochlorites can remove dried or fixed organisms and biofilms from surfaces (CDC). On a house, that means organic growth like the algae, mildew and lichen that darken siding and roofs. A surfactant lowers water's surface tension so the solution spreads and clings, and it surrounds oily dirt so the rinse can carry it away (ACI). The roofing industry's own cleaning guidance follows the same pattern: apply, let it dwell, then rinse with low-pressure water (ARMA).

Why siding and roofs get a soft wash

• Manufacturers limit pressure. James Hardie recommends a garden hose and soft brush for its fiber cement siding, and under 1,500 PSI from at least 6 feet if a pressure washer is used (James Hardie). Georgia-Pacific warns that aiming upward can drive water behind vinyl siding (Georgia-Pacific), and ProVia strongly discourages pressure washing its vinyl siding at all (ProVia).
• Roofs can't take it. ARMA says never to pressure wash an asphalt shingle roof, because it causes granule loss and very likely premature failure (ARMA).
• Growth isn't just on top. Mildew is a fungus whose thread-like hyphae branch across and into the surface (Cornell), so force alone removes what's visible and leaves the rest. The USDA Forest Service notes that mildew will return if the growth conditions remain the same (USDA Forest Service).

Our soft wash goes on through an X-Jet nozzle, which mixes in the cleaning solution at the nozzle and can reach up to 40-plus feet from the ground, according to its maker (X-Jet). Concrete gets our 3,000 PSI, 5.5 GPM cold-water pressure washer with a 20-inch surface cleaner. ACE takes roof jobs, including tile and metal, when the roof can be cleaned safely. Ask us.

Go deeper: Does PSI really matter? · Why bleach alone doesn't clean · What dwell time means · Why mildew grows back · Why a roof should never be pressure washed · The dangers of etching