Most people use “power washing” as a catch-all for any high-pressure cleaning. The truth is there are two methods, and using the wrong one on the wrong surface is how you end up with stripped paint, ruined shingles, or water behind your siding. Here is how to tell which one you actually need.
Power washing in plain English
Power washing uses high-pressure water, sometimes heated, to physically blast dirt off a hard surface. Pressure typically runs from 1,500 to 3,500 PSI. It is the right tool for surfaces that can take force without damage: concrete, brick, paver patios, stone, unsealed wood decks, fences, and most exterior tile.
The advantage is speed and depth of clean. The risk is damage if you point a high-pressure stream at the wrong material.
Soft washing in plain English
Soft washing uses very low pressure (under 500 PSI, basically like a strong garden hose) combined with detergents and biocides that kill mildew, algae, and moss at the root. Instead of blasting the dirt off, you let the cleaning agents do the work and rinse it away.
This is the right tool for delicate surfaces: roof shingles, painted wood siding, stained cedar, vinyl, stucco, and anything that water can sneak behind.
Match the surface to the method
Use this as a quick reference:
- Concrete driveway: Power wash. Hot water if there are oil stains.
- Vinyl siding: Soft wash. High pressure can crack the panels and force water behind them.
- Painted wood siding: Soft wash. Power washing strips the paint.
- Asphalt-shingle roof: Always soft wash. Pressure tears the granules off and shortens shingle life by years.
- Composite deck: Power wash with a wide fan tip and lower pressure.
- Cedar deck: Power wash gently or soft wash. Cedar is soft and gouges easily.
- Brick or stone walls: Power wash. Brick handles pressure well.
- Stucco: Soft wash. High pressure pits stucco.
- Patio pavers: Power wash, then re-sand the joints if the wash blew the joint sand out.
- Fence: Depends on the wood. Cedar and pine: gentle. Pressure-treated: power wash is fine.
What goes wrong when people pick wrong
The most expensive mistake is power washing a roof. We have seen DIY jobs where the homeowner stripped half the granules off their shingles in an afternoon. The roof passed the eye test for a few weeks and then started leaking the next winter.
Other common ones: vinyl siding panels cracked by direct pressure, paint peeled off cedar shake siding, stucco pitted and now needing patching, water blasted up under siding and rotting the sheathing.
If you are not sure which method is right, the safe call is always soft wash. You will never damage anything with low pressure and the right detergent. The only downside is it takes longer.
What Alpine actually does
We use both methods. Our heated SteamLux™ trucks can dial down to soft wash pressure and dial up to full power washing depending on what we are cleaning. The technician walks the property first and figures out which method goes on which surface. That is the part most cheap rigs cannot do, because they only have one setting.
How to ask a contractor about it
If you are getting quotes from anyone other than us, ask two questions: “What pressure are you using on the siding?” and “Are you soft washing the roof?” If they say “high pressure” to either one, find someone else. Or just call us at 206-501-2223 and we will give you a free quote and tell you exactly what each surface needs.
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