The short answer: pressure washing relies mostly on the force of the water, while soft washing relies on low pressure and a cleaning solution that's given time to work. Which one fits depends on the surface being cleaned.
What pressure washing is
Pressure washing uses a concentrated, high-pressure stream to blast dirt off a surface. It's well suited to hard, durable surfaces such as concrete driveways, sidewalks and parking lots, where the force is what lifts embedded grime. On flat concrete, a rotary surface cleaner spreads that force evenly and helps avoid streaks.
What soft washing is
Soft washing applies a cleaning solution at low pressure, lets it work on dirt and organic growth like algae and mildew, then rinses it off gently. It's the usual choice for siding, painted surfaces, stucco, trim and other materials where high pressure could cause damage or push water where it shouldn't go.
Why the surface decides
Siding is a good example. The Polymeric Exterior Products Association, which represents vinyl and polymeric siding makers, says a power washer can be used on that siding, but with caution. It notes that some manufacturers discourage power washing, while others limit the pressure and the cleaners that can be used. It also warns against aiming the stream upward, because that can force water behind the panels.
That's why a good cleaning plan starts with the material, not the machine. Older paint, failed caulking and existing damage can react to any washing, so they should be pointed out before work begins.
Many homes need both
A typical home might get a soft wash on the house and a pressure wash on the driveway and sidewalk in the same visit. The point isn't to pick one method for everything, but to use the right one on each surface.
Where the water goes
Cleaning solutions shouldn't end up in storm drains. In Dallas, for example, the city says wash water mixed with soap or cleaning chemicals must be kept out of storm drains and collected, while chemical-free wash water may be discharged only under certain conditions. Other cities have their own rules.
Questions to ask any cleaning company
- Which method will you use on each surface, and why?
- How will you protect plants, fixtures and openings?
- How will you handle wash water at my property?
- What should I expect if a stain doesn't fully come out?