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Contractor glossary

Soft washing

Updated

Definition

Soft washing is cleaning a surface with a cleaning solution applied at low pressure, left to work, then rinsed gently. The chemistry does the cleaning instead of water pressure, which is why it's used on siding, roofs and other surfaces high pressure can damage.

Also called: Soft wash, Low-pressure washing

How it works

Pressure washing uses force to blast dirt off. Soft washing uses a mix, usually built on sodium hypochlorite (the active ingredient in bleach) plus a surfactant that helps it cling, to kill and loosen mildew, algae and dirt. You apply it at low pressure, give it time to work (the dwell time), then rinse at low pressure.

The mix is applied one of two ways:

  • Downstream injector. It draws chemical into the pressure washer's low-pressure stream after the pump, so what reaches the wall is much weaker than what's in the bucket. Fine for lower walls and light growth.
  • Dedicated soft wash pump. It sprays solution at the strength you mixed, which roofs and heavy growth often need.

Example: Say your injector draws roughly 1 part chemical for every 10 parts water (check your own injector's real ratio). A bucket mixed for a roof would reach the wall far weaker than you meant. That's why washers run heavy growth and roofs through a dedicated pump instead of a bigger dose in the injector.

Where it's used

Siding (vinyl, painted wood, stucco, brick), gutter faces, fences and roofs are soft wash work. Concrete flatwork is usually cleaned with pressure and a surface cleaner instead.

Roofs show why the method matters. The Asphalt Roofing Manufacturers Association says never to pressure wash an asphalt shingle roof because it causes granule loss and likely premature failure. For algae and moss it describes a 50:50 mix of laundry-strength liquid chlorine bleach and water, applied gently with a sprayer, left to dwell and rinsed with low-pressure water, and it warns against scrubbing, which can loosen granules 1 2. It also notes the cleaning is temporary and the discoloration may come back 1, so tell customers that up front and offer a repeat visit.

Always follow the shingle or siding maker's care instructions and the cleaning product's label for the specific job.

Common mistakes

  • Calling it "pressure washing" on the quote. Name the method for each surface so the customer and your crew know what to expect.
  • Forgetting the plants. Runoff from walls and downspouts can burn landscaping. Wet, cover, redirect and rinse.
  • Mixing chemical families. Bleach labels typically warn that mixing it with acids or ammonia releases hazardous gas, and many rust removers and brighteners are acid-based. Read each product's safety data sheet and give each chemical family its own bucket, tank and pump.
  • Working in hot sun or rain. Heat dries the mix before it works; rain dilutes it.
  • Treating "low pressure" as "low risk." Roofs are still fall hazards, and the solution makes them slick.

How it connects

Spell out surfaces, methods, plant protection and pre-existing damage in your scope of work. Roof work brings in roof pitch and fall protection, and the damage this work can cause is a question for your general liability insurance agent. If you advertise that you kill mold, mildew or algae, ask your state's pesticide regulator whether that brings in licensing or labeling rules.

Go deeper

Pressure washing guideHow to Start a Pressure Washing BusinessStarting a pressure washing business: choosing services, washwater rules, soft wash chemical safety, sizing gear by PSI and GPM, roofs and insurance.Pressure washing guideHow to Write a Pressure Washing EstimateHow to write a pressure washing estimate: measure each surface, name the method, plan water and runoff, protect plants, and put disclaimers and photos in writing.Pressure washing guideHow to Price Pressure Washing JobsPrice pressure washing from your own production rates: square foot, job and hourly pricing, minimums, chemical and water costs, surcharges and bundles.Pressure washing guideHiring Your First Pressure Washing EmployeeWhat to settle before your first pressure washing hire: bleach and chemical safety, injection injuries, ladders and power lines, fragile surfaces, comp and pay.
Scope of workA scope of work is the written description of exactly what a job includes and what it excludes: the tasks, materials, quantities, locations and standards of finish. It's the part of an estimate or contract that defines what the price buys, so anything outside it needs a change order.EstimateAn estimate is a contractor's expected price for a job, based on the scope as it's understood before work starts. It tells the customer the price could change if the work turns out different, but whether it binds you depends on its wording, the customer's acceptance and your state's law.Fall protectionFall protection is the equipment, setup and training that keep workers from falling, or stop a fall safely, when they work at height. In residential construction, OSHA requires employers to protect each employee working 6 feet or more above a lower level, usually with a guardrail, safety net or personal fall arrest system.General liability insuranceGeneral liability insurance covers claims that your business injured someone who doesn't work for you or damaged their property, including the cost of defending the claim. It doesn't cover your own employees' injuries, your tools or vehicles, or redoing your own faulty work.Workmanship warrantyA workmanship warranty is your promise to fix, at no charge for a set period, problems caused by how you installed or did the work. It stands behind your labor; defects in the equipment or materials themselves fall under the manufacturer's warranty.Roof pitchRoof pitch is how steep a roof is, written as the inches it rises for every 12 inches of horizontal run, such as 6/12. Pitch decides how much real surface sits over a footprint, how fast crews can work and what safety setup and materials the roof needs.

See every term in the glossary

Sources

  1. Algae Discoloration of Roofs Asphalt Roofing Manufacturers Association
  2. Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems Asphalt Roofing Manufacturers Association

Rules and figures change, and many requirements vary by state and city. Check the current version of each source and your local authority before acting, and talk to a licensed professional about your specific situation.