Two methods, two very different approaches
When your home's siding looks dark, your roof has black streaks, or your deck has turned gray and slippery, the instinct is to blast it with a pressure washer. It makes sense — the grime is there, water pressure removes it. But the way the dirt is removed matters just as much as whether it gets removed at all.
There are two main methods used in professional exterior cleaning: pressure washing and soft washing. They look similar from the outside, but they work completely differently — and knowing which one your home needs can save you from expensive repairs down the road.
What is pressure washing?
Pressure washing uses high-pressure water — typically between 1,500 and 4,000 PSI — to physically blast contaminants off a surface. The force of the water does the cleaning. There's usually little to no chemical solution involved.
Pressure washing works well on hard, durable surfaces that can handle the force:
- Concrete driveways and walkways
- Brick patios and retaining walls
- Concrete block foundations
- Bare stone or pavers
On these surfaces, high pressure is effective and the material is durable enough to handle it. But apply that same pressure to vinyl siding, a painted wood deck, or an asphalt roof — and you're asking for trouble.
What is soft washing?
Soft washing uses very low water pressure — often no more than what comes out of a standard garden hose — combined with professional-grade, biodegradable cleaning solutions. Instead of using brute force to blast off dirt, the solutions do the work: they break down and kill mold, mildew, algae, and bacteria at a molecular level.
The result is a deeper, longer-lasting clean. You're not just removing surface staining — you're eliminating the organism causing it. That's why a soft wash on a roof can keep algae from returning for two or three years, while pressure washing the same roof might produce visible results for only a few months before the algae grows back.
"Soft washing kills the mold and algae at the root. Pressure washing just moves it around. The clean looks the same at first — but six months later, there's a big difference."
Side by side: pressure washing vs. soft washing
| Factor | Pressure Washing | Soft Washing |
|---|---|---|
| Water pressure | 1,500–4,000+ PSI | 100–500 PSI |
| Cleaning agent | Water only (usually) | Biodegradable solutions |
| How it cleans | Mechanical force | Chemical action |
| Results last | Months | 1–3 years |
| Risk to siding | High (can crack, warp, force water behind) | None |
| Risk to roof | Very high (strips granules, voids warranties) | None |
| Best for | Concrete, brick, stone | Siding, roofs, wood, decks |
Why pressure washing siding and roofs is a mistake
Vinyl siding might look tough, but high-pressure water can crack it, warp it, and — most commonly — force water behind the panels. Once water gets behind your siding, you're looking at potential mold growth inside your walls, rot, and insulation damage. Most vinyl siding manufacturers explicitly warn against pressure washing in their care guidelines.
Asphalt shingle roofs are even more vulnerable. High pressure strips the protective granules off shingles — the same granules that reflect UV rays and protect against weathering. Once those granules are gone, you've shortened the life of your roof significantly. Many roofing warranties are voided the moment a pressure washer touches the shingles.
Wood decks and fences are another common casualty. Pressure washing can raise the grain, splinter the wood, and drive water deep into the fibers, accelerating rot. If you're planning to stain or seal after cleaning, a raised grain makes for a rougher, less even finish.
When is pressure washing the right call?
Pressure washing absolutely has its place. For concrete driveways, walkways, and patios — surfaces that are dense, non-porous, and built to handle force — high pressure is effective and efficient. The same goes for certain brick and stone surfaces where you want to remove embedded grime without chemicals.
The key is matching the method to the material. We use pressure washing when the surface calls for it, and soft washing everywhere else.
What we use at Giani Exterior Services
For the vast majority of exterior cleaning in New Hampshire — house washing, roof washing, deck cleaning, fence cleaning — we use soft washing. Our solutions are biodegradable and safe for your family, pets, and landscaping. We rinse surrounding plants before and after every job.
For driveways and concrete, we use pressure washing with the appropriate PSI for the surface. Every job gets the right tool and the right method.
If you've been quoted a pressure wash for your siding or roof, ask questions. It's worth knowing what's actually going to touch your home — and whether it could cause damage that costs far more than the cleaning itself.
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We'll take a look and recommend the right approach — no pressure (pun intended).
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