If you ask three pressure washing companies to clean your house, you'll get three different proposals — and one of them might damage your siding. The single most important distinction in this trade is pressure washing vs soft washing, and most homeowners have never heard the term.
Here's the difference, why it matters, and which technique is right for each surface on your property.
The two techniques in one sentence each
- Pressure washing: high-PSI water (2,000–4,000 PSI) blasts dirt off hard surfaces.
- Soft washing: low-PSI water (under 500 PSI) plus a cleaning solution (typically sodium hypochlorite + a surfactant) chemically kills mold, mildew, algae, and bacteria on contact.
That's it. The difference is whether the cleaning is done with mechanical force (pressure) or chemistry (soft wash).
Which surface needs which
| Surface | Right technique | Why |
|---|---|---|
| Concrete driveway | Pressure | Tolerates 3,000+ PSI, dirt is mechanical |
| Brick + mortar | Soft (mostly) | High pressure erodes mortar over years |
| Vinyl siding | Soft | Pressure forces water behind seams; mildew is the actual problem |
| Wood siding / cedar | Soft | Pressure splinters and removes wood grain |
| Painted surfaces | Soft | Pressure strips paint |
| Asphalt shingles (roof) | Soft, ALWAYS | Pressure removes granules → roof voids warranty + fails early |
| Wood deck | Soft + low pressure | Pressure splinters; soft prevents algae |
| Pavers / flagstone | Pressure (medium) | Tolerates pressure; high settings can dislodge sand joints |
| Vinyl fence | Soft or low pressure | Vinyl tolerates pressure; mildew wants chemistry |
Why this matters for your house
The most common pressure-washing damage we see:
- Vinyl siding seam damage. High-pressure water forces between panels and into the wall cavity. Mold grows behind the siding for months. By the time you see it, it's a $5,000–$20,000 wall reconstruction job. The cleaner who "saved you $200" cost you $20,000.
- Roof shingle damage. Asphalt granules are what give shingles their UV protection and 25-year lifespan. A pressure wash strips granules; the roof loses 5–10 years of life. Most insurance won't cover damage from improper cleaning.
- Wood splintering. A 3,000 PSI nozzle on a cedar deck takes wood off in stripes. Sealing won't fix it.
- Mortar erosion. Old brick (pre-1950) often has lime mortar that erodes at modern pressure-washer settings. Once mortar is gone, water gets behind the brick.
The two questions that protect you
When getting quotes:
- "Will you soft wash my vinyl siding (or roof)?" The right answer is yes, with explanation. The wrong answer is "we use pressure on everything." If they don't know the difference, they're not who you want.
- "What chemicals do you use, and how do you protect my landscaping?" Sodium hypochlorite (the active ingredient in most soft-wash chemicals) burns plants. A real pro pre-wets your shrubs and lawn, then rinses thoroughly afterward. If they don't, you'll lose plants.
What about "low pressure washing" or "house wash"?
Many operators advertise a "house wash" service that's actually soft wash. Same thing, friendlier marketing language. Some operators advertise "low pressure" — they mean turning their pressure washer down. That's not real soft wash; it's diluted pressure wash, which still relies on mechanical force and doesn't kill the underlying mildew.
Real soft wash uses a dedicated soft-wash setup: a tank, a low-pressure pump, a mixing system for the cleaning solution, and a long wand or down-stream injector. If the operator's truck has only a pressure washer with no soft-wash tanks, they don't actually do soft wash.
Pricing implication
Soft wash and pressure wash are typically priced the same per square foot, even though soft wash uses more chemicals. Don't pay extra for "soft wash upgrade" — that's a markup. The right operator quotes the technique appropriate for the surface and prices the job, not the technique.
FAQ
Can I soft wash my own house? Technically yes, but the chemicals (sodium hypochlorite is industrial bleach at higher concentrations) are corrosive and need careful handling and dilution. The cost of a DIY soft-wash kit is similar to one professional job, so it only pays off if you'll do this yearly for a decade.
How often should I have it done? Vinyl siding: every 2–3 years (every year if your house is shaded or near woods). Roof: when black streaks become visible (every 2–4 years in humid climates). Driveway: every 1–2 years.
Will soft wash kill my plants? Sodium hypochlorite at the dilutions used for soft wash is risky to plants if they aren't pre-wetted and rinsed. A pro pre-soaks the soil, sprays a tarp barrier on delicate shrubs, and rinses everything when finished. Damage is rare with experienced operators, common with inexperienced ones.
What's the smell during a soft wash? Mild chlorine smell during the cleaning, gone within an hour after rinse. If the smell lingers for days, the operator over-applied chemicals.