Soft washing, and how to tell it from a pressure washer with new marketing

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

• The surface is not biological. Soft washing kills living growth. Rust bleed from a fastener, tar staining, paint overspray and mineral deposits are not alive and will not respond, whatever solution is used on them.
• Your roof is a bare or unpainted metal that reacts with chlorine-based solutions. The default soft-wash chemistry is not universal. Bare galvanised and some coated panels need a different approach, and an operator who runs one mix on everything is the wrong hire for a metal roof.
• You want a guaranteed like-new finish on heavy lichen. Lichen grips into the granule surface and often leaves a ghost. If a spotless result is the requirement, the honest answer may be that the roof is at the end of its cosmetic life rather than that it needs a harder wash.
• The shingles are already brittle and shedding. Soft washing is gentle, but the crew still has to get across the roof. On a roof that cracks under foot, even the correct method carries a cost.
• You are cleaning to hide a problem before a sale. A washed roof over lifted shingles or a soft deck fails an inspection anyway, and the buyer's inspector will look harder at a roof that has obviously just been cleaned.
• Rain is forecast within the hour. Application washed off before it has worked is money spent for nothing. A crew that pushes ahead regardless is optimising for their schedule, not your result.

Chlorine-based cleaning solutions are harmful to eyes, skin and lungs, and must never be mixed with anything containing ammonia or acid. Combine that with a wet sloped surface at height and you have the two most common ways this job sends people to hospital. Read the product label before you open anything.

• What equipment do you use to apply, and what pressure does it run at?

  You are listening for a low-pressure chemical pump. "Our pressure washer on a low setting" is a different answer and a different risk.

• How long will the solution be left on the roof before you rinse?

  Dwell time is where soft washing does its work. An operator who has no answer is planning to substitute force for patience.

• What are you applying, and can I see the product label or safety data sheet?

  You do not need to be a chemist. You need the operator to be willing to name what is going on your house and near your plants.

• Is my roof material suitable for your standard mix, or does it need something else?

  Asphalt, concrete tile, clay tile and coated metal do not all take the same treatment. One-mix-for-everything is a warning sign.

• What happens if the stains do not fully lift?

  Settle this before the crew is on the roof deciding for themselves. The wrong answer is a second pass with more pressure.

• Does your warranty cover regrowth, damage, or both?

  These get conflated deliberately in this trade. A regrowth guarantee says nothing about who pays if your shingles are stripped.

• Who is responsible if the runoff kills my planting?

  Ask before, in writing. Afterwards it becomes a dispute about whether the plants were already struggling.

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