Soft wash — chemistry-driven, low pressure
A soft-wash rig uses a 12V diaphragm pump or air pump to push a sodium hypochlorite + surfactant mix through a large-orifice nozzle at 60-200 PSI. The chemistry kills mold, mildew, and algae at the cellular level. The water just delivers the chemistry and rinses. Dwell time is 5-15 minutes before rinse.
- Use on: vinyl siding, painted siding, wood siding, brick, stucco, EIFS, asphalt-shingle roof, metal roof, fence, deck (carefully).
- Why low pressure matters: high pressure drives water behind siding laps into wall cavities, strips paint, breaks caulk seals, and on roofs dislodges shingle granules and voids warranties.
- Chemistry: typically 1.5-2% SH at the surface for house wash, 3-4% SH for roof wash, with surfactant for adherence.
Power wash — mechanical, high pressure
A power washer puts out 1,500-4,000 PSI through a small-orifice nozzle at high velocity. Water alone does the work — mechanical force scours dirt, oil, tire marks, and embedded stains off the surface.
- Use on: concrete driveway, paver, brick walkway, concrete steps, retaining wall, dumpster pad, equipment exterior.
- Why high pressure works here: concrete and paver are non-porous and structurally tough enough to take mechanical force. Embedded oil and tire marks don't respond to chemistry alone.
- Optional surface cleaner: a rotating-arm surface cleaner attached to a 4 GPM hot-water unit is the productivity tool — cuts driveway time roughly in half.
Common mistakes
- Power washing vinyl siding. Water in the wall cavity. Mold. Rot. Callbacks that end the relationship.
- Power washing a shingle roof. Granule loss, voided warranty, leaks within 2-3 years.
- Soft washing only on a driveway. Kills the green/black but leaves oil and tire marks intact. Customer feels ripped off.
- Soft wash without surfactant. SH runs off the wall before it can dwell. No cleaning happens.
- Power washing without rinsing chemistry first. Concentrated SH dries on the surface and etches glass and aluminum.
Quick decision tree
- Painted, porous, or above 8 feet of elevation? Soft wash.
- Concrete, paver, or stone hardscape with embedded stains? Power wash.
- Both on the same job? Soft wash first (siding + roof), then power wash the driveway. Reversed order risks runoff staining the siding you just cleaned.
Render the right service on every surface, automatically.
Free account, free rendering, $1 per mailed postcard. The render shows soft-washed siding + power-washed driveway in one image.
Start free →