What Is Soft Washing?

Soft washing is a cleaning method that replaces pressure with chemistry. Instead of forcing water at a surface hard enough to knock growth off it, a solution is applied at low pressure, given time to work, and rinsed away.

It exists because a great many exterior surfaces cannot survive being pressure washed, and in the Pacific Northwest most of what needs cleaning is biological rather than simply dirty.

The pressure difference in plain numbers

A pressure washer used on concrete typically runs somewhere between 2,000 and 4,000 PSI. A soft wash system applies solution at closer to 100 PSI, which is roughly what comes out of a garden hose with a nozzle on the end.

That is not a small adjustment to the same technique. It is a different job entirely. In a pressure wash, water does the work. In a soft wash, the solution does the work and the water only carries it on and off the surface.

What soft washing is used on

• Asphalt shingle roofs: pressure removes the granules that protect the shingle from sunlight
• Cedar siding and shakes: pressure raises the grain and leaves the surface permanently furred
• Painted lap siding and T1-11: pressure strips paint and forces water behind the cladding, where it cannot dry
• Stucco: pressure opens hairline cracks that then hold water through winter
• Vinyl siding: pressure drives water up behind the laps

Hardscape is the exception. Concrete, pavers and masonry are cleaned with genuine pressure, usually through a rotary surface cleaner rather than a wand, which is what keeps the finish even instead of striped.

Why it works better on living growth

Algae, moss and lichen are organisms with root structures or holdfasts that grip the surface. Pressure removes the visible part and leaves what is anchored, which is why a pressure-washed roof or north wall greens up again quickly.

A soft wash solution kills the organism rather than knocking the top off it. The surface stays clean longer because there is less left behind to regrow from.

What about the plants

The honest answer is that any solution strong enough to kill roof algae needs managing around landscaping. That is done by soaking beds with clean water before work starts, covering where run-off concentrates, and rinsing again afterwards. A crew that does not mention plants before starting has not planned for them.

How to tell which one your property needs

A rough rule: if the surface is porous, painted, or made of wood, it wants a soft wash. If it is concrete or stone and horizontal, it wants pressure. Most houses need both on the same visit, applied to different surfaces, which is why a single quoted price with no method named is worth questioning.

We use soft washing across the metro on roofs and siding. You can read more about house washing or call (503) 734-0317 to talk through your surfaces. Oregon CCB #260979p, $2,000,000 insured.

Blue Heron Services: Complete Exterior Care