The short answer
Soft washing uses controlled chemistry at low pressure (under 500 PSI) to dissolve and kill organic growth like algae and mildew. Pressure washing uses high-PSI water (1,500-4,000+ PSI) to physically blast surfaces clean.
For a typical home in North Georgia, you need both. Soft wash for siding, painted brick, stucco, and the roof. Pressure wash for concrete — driveway, walkways, patio, sometimes the deck.
An operator who only uses one method on every surface is doing it wrong.
Why soft washing is correct for siding and roofs
Vinyl siding, painted brick, stucco, and asphalt roof shingles can all be damaged by high-PSI water. Pressure-blasting siding can drive water behind the panels (rot risk). Pressure-washing a roof voids most asphalt shingle warranties and removes the granules that protect the shingles from UV.
Soft washing replaces brute force with chemistry. A blend of sodium hypochlorite and a surfactant kills the algae, mildew, and gloeocapsa magma at the root. The cleaning solution does the work, then a low-pressure rinse takes it away. The Asphalt Roofing Manufacturers Association (ARMA) explicitly endorses soft washing as the method for asphalt roofs.
Bonus: because soft washing kills the organic growth at the source, it stays clean for 12-18 months in North Georgia. Pressure-only on the same surface might look clean for 2-3 months before the green comes back.
Why pressure washing is correct for concrete
Concrete — driveway, walkway, patio, garage floor — is dense, hard, and can take real pressure. A surface cleaner (essentially a spinning bar with two pressure jets, encased in a circular shroud) gives you an even, edge-to-edge clean with no streaks. Trying to soft-wash a 20-year-old algae-coated driveway is slow, expensive, and won't lift the deeper staining the way a surface cleaner will.
Inside our menu: driveways, sidewalks, patios, and dumpster pads are all pressure-washed with a surface cleaner. House exteriors and roofs are soft-washed.
Decks and patios: it depends
Wood decks (pressure-treated) take 1,500-2,000 PSI safely. Cedar takes less. IPE and other hardwoods take more. Composite is soft-washed only.
Hardscape patios — flagstone, paver, brick — each get a different setting. Pavers especially: too much pressure blows out the joint sand and you trade a clean patio for a destabilized one. We use a 16-inch surface cleaner at the right PSI so the surface cleans evenly without lifting the joints.
How to tell if your operator is doing it right
Three things to ask. (1) Will you soft wash my siding/roof? Correct answer: yes. (2) What surface cleaner do you use on concrete? Correct answer: 16-inch or larger Whisper Wash, BE Big Guy, or equivalent. (3) Do you pre-rinse and protect my plants? Correct answer: yes — always, with fresh water, before any chemistry hits the house.
If the operator can't answer those three questions cleanly, hire someone else.