So what’s the difference between the two? The name gives a clue.
Pressure Washing utilizes high PSI or Pressure to clean a surface. The high pressure is expelled through a tool such as a wand, surface cleaner or ball valve. According to Wikipedia this is what pressure cleaning is:
Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, chewing gum and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure washer is expressed in gallons or litres per minute, often designed into the pump and not variable. The pressure, expressed in pounds per square inch, pascals, or bar, is designed into the pump but can be varied by adjusting the unloader valve. Machines that produce pressures from 750 to 30,000 psi (5 to 200 MPa) or more are available.
The terms pressure washing and power washing are used interchangeably in many scenarios, and there is some debate as to whether or not they are actually different processes.
A pressure washing surface cleaner is a tool consisting of two to four high-pressure jets on a rotating bar that swivels when water is flowing. This action creates a uniformed cleaning pattern that can clean flat surfaces at a rapid rate.
Hydro-jet cleaning is a more powerful form of power washing, employed to remove buildup and debris in tanks and lines.
Soft washing is a cleaning method using low pressure and specialized solutions (typically bleach, water, and sometimes a surfactant) to safely remove mildew, bacteria, algae and other organic stains from roofs and other building exteriors. It is so named to differentiate the method from power washing. The Asphalt Roofing Manufacturers Association recommends low-pressure bleach or detergent assisted washing as the preferred method for cleaning asphalt roofs in order to prevent damage to the shingles.
Here’s some IMPORTANT information from AMRA and GAF on Soft Washing:
Soft washing is using an electric agricultural sprayer to apply a water-based, biodegradable disinfecting cleaning solution to kill the mold, mildew, bacteria, algae, fungus, moss and more on exterior home and building surfaces.
Soft washing Equipment is distinctly different than power and pressure washing equipment. The electric diaphragm pump applies the cleaning solution at 40-80 PSI. The equipment used for soft washing may also have telescoping handles so that the cleaning solution can easily reach roof eaves, upper story windows, and other such areas, without this added pressure.