Key Takeaways
- Pressure washing uses high mechanical force (2,500 - 4,000 PSI) for dense hardscapes like concrete and brick.
- Soft washing uses low pressure (<100 PSI) and specialized biodegradable detergents for delicate roofs, siding, and stucco.
- High pressure on asphalt roofs strips protective granules and voids manufacturer warranties (ARMA guidelines).
- Soft washing chemically kills algae spores at the root, providing significantly longer-lasting results.
What Is Pressure Washing?
Pressure washing relies on mechanical force, spraying water at pressures between 2,500 and 4,000 PSI (pounds per square inch). It is engineered for tough, non-porous or heavy-duty surfaces that can withstand intense impact.
When combined with hot water (power washing), it excels at lifting embedded motor oil, tire marks, chewing gum, and hardened industrial grease from concrete driveways, commercial dumpster pads, and parking structures.
What Is Soft Washing?
Soft washing utilizes low pressure—comparable to the flow of a standard garden hose (under 100 PSI)—paired with specialized eco-friendly algaecides and foaming surfactants.
Rather than blasting away surface debris mechanically, soft washing chemically dissolves organic contaminants like Gloeocapsa magma (black algae), mold, mildew, lichen, and pollen at the root level, followed by a gentle freshwater rinse.
Surface Comparison: Which Method to Use Where
Choosing the correct technique depends entirely on the substrate material:
- Asphalt Shingle Roofs: ALWAYS Soft Wash (High pressure causes immediate granule loss and roof failure).
- Vinyl, Fiber Cement & Wood Siding: ALWAYS Soft Wash (Prevents cracked panels and water intrusion).
- Stucco & EIFS: ALWAYS Soft Wash (High pressure will gouge and pit the soft textured surface).
- Poured Concrete Driveways & Sidewalks: Pressure Wash with Rotary Cleaners.
- Commercial Dumpster Pads & Loading Docks: Hot-Water High-Pressure Power Wash.
David Hudson
David Hudson is the founder and hands-on lead technician at Steam On Wheels LLC with over 15 years of exterior pressure washing and soft washing expertise across Mooresville and Lake Norman, NC.