The fastest way to cause a damage claim is to point a high-pressure wand at the wrong surface. Soft wash versus pressure wash isn't a preference. It's a per-surface decision, and getting it right is most of the craft.
Soft wash: let the chemistry do the work
Soft washing uses low pressure plus a cleaning solution (usually sodium hypochlorite and a surfactant) that kills the algae, mildew, and lichen at the root so it rinses away. Use it on anything that high pressure would damage or that's biologically dirty:
- Roofs (shingle, tile, metal), always
- Siding (vinyl, stucco, painted wood)
- Screens, soffits, and delicate trim
- Fences and shaded, algae-streaked surfaces
The job is mix ratio and dwell time, not pressure. Rush the dwell or skip the pre-rinse on plants and you'll get streaks or dead landscaping.
Pressure wash: hard, durable flatwork
High pressure is right where the surface can take it and the dirt is mechanical, not biological:
- Concrete driveways, sidewalks, and patios
- Brick and stone flatwork
- Many composite and hardwood decks (dialed down)
Use a surface cleaner for even results, and keep the wand moving so you don't etch lines into concrete.
When in doubt, soft wash
If you're unsure whether a surface can take pressure, soft wash it. The downside of too-low pressure is a slower job; the downside of too-high pressure is a damaged roof and a refund. Document the surface and the before/after on the property either way. The photo record is your protection if a customer questions the result weeks later.