Soft wash vs pressure wash
Updated 2026-09-04
- Best overall
- It depends on the surface, and that is the answerNeither is better. Flatwork wants pressure; anything vertical, porous or roofed wants chemistry.
- Best for concrete
- Pressure washing, with a surface cleanerDense, horizontal and unglazed. A 20 in disc at 3,000-3,500 PSI is faster and better than any chemical alone.
- Best for the house
- Soft washing, every timeSiding, stucco, roofs and painted wood. Low pressure, dilute hypochlorite, a real dwell.
The difference in one table
| Spec | Soft wash | Pressure wash |
|---|---|---|
| Working pressure | 100–500 PSI | 1,200–3,500 PSI |
| What does the work | Chemistry and dwell | Mechanical force |
| Nozzle | Black soap, then 40 deg white rinse | 25 deg green, or a surface cleaner |
| Typical dwell | 5–20 min | None |
| Kills the growth | Yes | No — removes it only |
| How long it stays clean | Years | Months, unless post-treated |
| Risk of surface damage | Low | High on the wrong surface |
| Risk to planting | Real — manage with pre-wetting | Low |
“Our pick” is the soft-wash column, and only because more of the surfaces on a typical house belong to it. On a driveway the other column wins outright.
Soft washing
A dilute sodium hypochlorite solution with a surfactant, applied at garden-hose pressure, left to dwell, then rinsed. It kills the algae, mildew and lichen that make an exterior look dirty, which is why the result lasts — the growth is dead rather than displaced.
It is the required method on asphalt shingles: the manufacturers’ own association states that power washers, brushes and brooms should not be used on shingle roofs because high-pressure systems are likely to damage them. It is the sensible method on siding, where pressure drives water up behind the lapped courses, and on stucco and EIFS, where pressure can punch through the skin entirely.
Where it falls short: heavy oil, tyre marks, embedded grime on concrete. Chemistry alone will not shift those, and no amount of dwell substitutes for a surface cleaner.
Pressure washing
Mechanical removal. On concrete flatwork it is unmatched: a 20-inch surface cleaner at 3,000–3,500 PSI covers ground three or four times faster than a wand and leaves an even finish because the stand-off is fixed.
It is also the only realistic answer for petroleum staining, road film on commercial aprons, and anything that has been physically ground into a porous horizontal surface.
Where it falls short: everything vertical, everything porous, everything roofed. And on its own it removes without killing, which is why a driveway cleaned in March is green again by June unless it gets a hypochlorite post-treat.
Surface damage risk
Most jobs are both
A full house exterior is a soft wash on the walls, a pressure wash on the drive and walks, and a soft-wash post-treat on the concrete afterwards. That is one visit, one machine, and two methods — and knowing which surface gets which is the whole skill.
- Roof: soft wash, ~3% at the shingle, 15–20 minute dwell, gentle rinse.
- Siding: soft wash, 0.5–1.5% at the wall, surfactant, bottom-up then rinse top-down.
- Driveway and walks: pre-treat, surface cleaner at 3,000–3,500 PSI, edge with a 25-degree tip.
- Post-treat the concrete: ~0.75% hypochlorite, left on. This is the step that decides how long it stays clean.
How to explain it to a customer