Soft Wash vs Pressure Wash — Which Does Your House Need?

"Pressure washing" is the term most homeowners know — but it's actually two different methods, and using the wrong one on the wrong surface causes thousands of dollars in damage every year. We've been called out to repair the aftermath of "pressure washed" roofs that lost half their shingle granules, and painted siding that came off in strips because someone aimed a 3,500-PSI wand at it.

Here's the difference, and how to know which one your house needs.

What is Pressure Washing?

Pressure washing uses high-pressure water — typically 1,500 to 4,000 PSI (pounds per square inch) — to physically blast contaminants off a surface. There's no chemistry involved; it's pure mechanical force. The water itself does the cleaning.

This method is fast, effective on hard surfaces, and uses no chemicals. But it has two big limitations: it can't kill the organic growth (algae, mold, mildew) that returns days later, and it will damage anything softer than concrete.

When to use pressure washing

• Concrete driveways and sidewalks
• Brick and stone (in good condition, with solid mortar)
• Unsealed concrete patios and pool decks
• Industrial flooring and parking lots
• Heavy equipment and machinery

What is Soft Washing?

Soft washing uses low-pressure water — typically under 500 PSI, often as low as 100 PSI — combined with biodegradable cleaning solutions. The chemistry does the cleaning; the water just delivers and rinses.

Soft washing kills the algae, mold, and bacteria at the cellular level, which is why a soft-washed surface stays clean 3 to 5 times longer than a pressure-washed one. It's also safe for surfaces that high pressure would destroy.

When to use soft washing

• Asphalt shingle roofs (high pressure strips granules)
• Painted siding (high pressure peels paint)
• Vinyl siding (high pressure forces water behind the panels)
• Stucco (high pressure pits the surface)
• Cedar shake siding
• Wood decks and fences (only soft wash, never high pressure)
• Window screens
• Outdoor furniture

Side-by-Side Comparison

Factor	Pressure Wash	Soft Wash
Pressure	1,500–4,000 PSI	Under 500 PSI
Cleaning agent	Water only	Detergent + sodium hypochlorite
Best for	Concrete, brick, hard surfaces	Roofs, siding, painted, wood
Kills algae/mold	No (blasts it off)	Yes (chemistry kills cells)
Results last	6–12 months	3–5 years (roof), 12–18 months (siding)
Damage risk	High on soft surfaces	Very low

What Does Sodium Hypochlorite Do?

Sodium hypochlorite — basically the active ingredient in pool chlorine, diluted appropriately — is the workhorse chemical in professional soft washing. It oxidizes the cell walls of algae, mold, and bacteria, killing them at the root. Once dead, the organic matter rinses off easily and doesn't immediately re-colonize.

The ARMA (Asphalt Roofing Manufacturers Association) specifically recommends sodium hypochlorite soft washing for cleaning algae-stained asphalt shingle roofs. It's the only method that doesn't void shingle warranties.

The Costly Mistakes

Mistake 1: Pressure washing an asphalt roof

High pressure strips the granular coating off shingles. Granules protect shingles from UV. Without them, the asphalt dries out and the roof fails years early. A $400 "pressure washed roof" can lead to a $15,000 early roof replacement.

Mistake 2: Pressure washing painted siding

Anything over 1,500 PSI on painted wood or composite siding will lift the paint. You'll see peeling within weeks. This is a $4,000–$8,000 repaint job that wasn't needed.

Mistake 3: Pressure washing stucco

Stucco looks tough but is actually quite porous. High pressure pits the surface and forces water behind, which can cause mold inside the wall cavity. Stucco wants soft wash only.

Mistake 4: Soft washing without rinsing

This is a contractor mistake, not a method mistake. Sodium hypochlorite needs to be rinsed off plants, grass, and the home itself after dwell time. Skipping this step leaves chemical residue. Always confirm your contractor pre-rinses and post-rinses landscaping.

The Hybrid Approach

Most houses need both methods, applied to different surfaces. A standard PrimeStar Wash visit might look like:

• Roof: Soft wash (low pressure + sodium hypochlorite)
• Siding: Soft wash (low pressure + surfactant)
• Driveway: Surface-cleaner pressure wash + degreaser pre-treatment
• Sidewalks: Pressure wash
• Wood fence: Soft wash + brightener
• Patio: Pressure wash (if concrete) or soft wash (if wood)

How to Ask a Contractor the Right Way

When you call for a quote, don't ask "do you pressure wash?" Ask:

• "What method do you use on roofs?" (Correct answer: soft wash)
• "What pressure do you use on painted siding?" (Correct answer: under 500 PSI)
• "Do you pre-rinse and post-rinse landscaping?" (Correct answer: yes, both)
• "What chemicals do you use, and are they biodegradable?" (They should answer specifically)

If they say "we use 4,000 PSI on everything" — call someone else.