The short answer
Soft washing uses a cleaning solution at low pressure to kill and remove growth. Pressure washing uses force and flow to remove dirt from hard surfaces. Painted, coated, and soft surfaces get soft washed. Concrete gets pressure washed.
Soft wash these
- Roofs, both shingle and tile
- Stucco, painted block, and siding
- Screen enclosures and pool cages
- Vinyl fences, soffits, and gutters
Pressure wash these
- Driveways and sidewalks
- Concrete patios and pool decks
- Parking lots, dumpster pads, and drive-thrus
- Storefront walks with gum and grime
What goes wrong
High pressure on a shingle roof strips the granules. On stucco it can etch the finish and drive water behind it. On a screen it tears the mesh. Too little effort on concrete leaves stripes and a blotchy finish. Matching the method to the surface is most of the job.