The short answer
Soft washing applies a cleaning solution at low pressure, typically 100 to 300 PSI, and the solution kills algae, mold and mildew. Power washing uses 3,000 PSI or more of water force. Siding, roofs, stucco and wood get soft washed. Concrete driveways and stone flatwork get power washed. Using the wrong method causes damage many homeowners blame on weather.
The Difference Is Not Pressure. It Is Chemistry.
Many homeowners in Macomb County picture these two services as the same thing at different intensities, like a dimmer switch. They are not. They are two different cleaning methods, and confusing them is an expensive mistake in exterior cleaning.
Power washing removes what is sitting on a surface using mechanical force. Water hits grime hard enough to knock it loose. That works well on concrete, which is hard enough to take high pressure through a surface cleaner, though a wand held too close can still etch it.
Soft washing removes what is growing on a surface using chemistry. The organisms staining your siding and roof (algae, lichen, mildew, moss) are alive. A cleaning solution kills the colony, including the cells lodged in the surface pores. Then low-pressure water rinses the dead growth away. Nothing is blasted. Nothing is forced.
Here is the part that matters: pressure removes growth but does not kill what it leaves behind. You can blast algae off a north-facing wall and it will look clean that afternoon. Cells left in the pores of the surface are still alive, and the growth returns within months, which is why so many people believe exterior cleaning "doesn't last."
The short version: If the surface can be dented, etched, waterlogged or lifted, it gets soft washed. If it is a solid mineral surface bonded to the ground, it gets power washed.
Which Surfaces Need Soft Washing?
Soft washing is the correct method for most of what you can see from the street: siding, roofs, trim and wood. Brick walls are a middle case. The Brick Industry Association's Technical Note 20 says not to use water pressure above 400 psi at the nozzle unless the brick manufacturer permits more, so brick gets a low-pressure rinse rather than a pressure wash.
- Vinyl siding: high pressure aimed upward drives water behind the panels, where it sits against the sheathing and can grow mold you cannot see
- Asphalt shingle roofs: pressure strips the ceramic granules that give the shingle its UV protection, and the Asphalt Roofing Manufacturers Association says not to use a power washer on a roof at all
- Wood decks, fences and cedar: pressure tears out the soft growth between grain lines, leaving a furry surface (see cleaning a wood fence before staining)
- Composite decking (Trex, TimberTech, Azek): follow the maker's care guide. Trex allows a pressure washer up to 3,100 psi on its current lines with a fan tip held at least 8 inches from the boards, TimberTech caps it at 1,500 psi, and Trex notes that products containing bleach or acid will lighten its surface
- Stucco and Dryvit: pressure cracks the finish coat and lets water into the wall assembly
- Painted surfaces, soffits, fascia and gutters: pressure lifts paint and dents aluminum
- Windows and screens: direct pressure can break the seal on double-pane glass, which is a costly repair
Many homes in subdivisions across Macomb Township, Chesterfield and Shelby Township are vinyl-sided, and that exterior should be cleaned with a solution at low pressure rather than a pressure wand. A proper professional house washing never puts high pressure on your walls.
What the Solution Does
A soft wash mix is a diluted sodium hypochlorite (bleach) solution with a surfactant that helps it cling to vertical surfaces long enough to work. It is applied at low pressure, allowed to dwell for several minutes while it breaks down the organism, then rinsed. Bleach is never mixed with acid-based cleaners or ammonia, which release toxic gas; when a job also calls for an acid product such as a wood brightener, the surface is rinsed between steps.
The dwell time is the job. A crew that sprays and immediately rinses has not killed anything; they have washed the surface with soapy water. This is what "splash-and-dash" means in our trade, and it is why dwell time is worth asking about before you book.
Which Surfaces Need Power Washing?
High pressure belongs on hard, mineral surfaces where the goal is removing embedded material rather than killing something alive.
- Concrete driveways, sidewalks and aprons
- Concrete pavers and stone patios (at lower pressure than poured concrete)
- Garage floors
- Commercial loading docks, dumpster pads and parking structures
- Retaining walls and hardscape
Even here, technique separates results. A wand held too close leaves "zebra stripes": visible bands where the operator's arc overlapped unevenly. A surface cleaner, which is the round rotating tool you have seen commercial crews walk across a lot, spins two jets under a shroud at a fixed height and produces an even finish. Professional concrete cleaning relies on one for the flat areas. Wand work is for edges and detail.
A Simple Comparison
| Soft Washing | Power Washing | |
|---|---|---|
| Pressure | Under 500 PSI, typically 100–300 | 3,000–4,000 PSI on poured concrete; about 1,500–2,500 on concrete pavers |
| What does the work | Cleaning solution | Water force |
| Kills the organism | Yes | No, removes surface growth only |
| Typical result lasts | 2–3 years on shaded walls, longer in sun | Organic growth returns sooner, because live cells remain |
| Correct for | Siding, roofs, wood, stucco | Concrete, pavers, stone flatwork, hardscape |
| Risk if misapplied | Landscaping damage if not pre-wet and rinsed | Etched concrete, damaged siding, stripped shingle granules |
How to Tell What a Company Does
Anyone can put the phrase "soft wash" on a website. Three questions tell you how a company will clean your house:
- "What PSI do you use on siding?" A clear answer is a number under 500. If the answer is vague, ask what equipment goes on the walls.
- "How long does your solution dwell before you rinse?" There should be a specific answer in minutes. "We rinse right away" means nothing was killed.
- "How do you protect the landscaping?" A good answer: pre-wet the beds before application, control runoff, and rinse thoroughly after. Pre-wetting reduces the risk to plants; it does not remove it, which is why the after-rinse matters too.
What This Looks Like on a Real House
A typical two-story colonial in Southeast Michigan is not one job. It is several methods on one property:
- Roof: soft wash, with as little walking on the shingles as possible
- Siding, soffits, fascia, gutters: soft wash
- Windows and screens: hand detail or low-pressure rinse
- Driveway, walkway, porch: power wash with a surface cleaner
- Deck: soft wash on a lower-strength mix, then a dedicated brightener on wood, rinsed between steps
One machine at one setting across all of those surfaces tends to damage something. Usually it is the siding, occasionally the roof, and the homeowner rarely connects the two events because the failure shows up months later as a warped panel or a stain that will not come out.
The Bottom Line
Ask which method a company plans to use on each surface before you book. If the answer is the same for your roof and your driveway, ask why. The correct approach is not a preference or a sales angle. It is set by what the surface is made of, and any crew doing this properly can tell you why in one sentence per surface.
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