Does soft washing use hot water?

Read each roofing document for the water it uses and the pattern is the same every time: the water is named, and its temperature is not.

• Asphalt shingle, ARMA. The Asphalt Roofing Manufacturers Association's technical bulletin ends its procedure by telling the reader to “rinse the solution from the roof by gently spraying the surface with water.” Its algae and moss bulletin says “rinse thoroughly with low pressure water.”
• Asphalt shingle, GAF. GAF's bulletin says to apply its mixture with a garden sprayer and “rinse with low-pressure water.”
• Metal, the Metal Roofing Alliance. Its detergent solution stands 5 to 10 minutes “before thoroughly rinsing the surface with plain water.”
• Concrete tile, Eagle Roofing Products. Eagle recommends that a tile roof cleaning “use only water” with the water pressure never exceeding 1200 psi, its figure for concrete tile.

Pressure turns up in those lines, and so do minutes, measured amounts and the kind of sprayer. Heat does not. Even GAF, whose mixture lists water, bleach and TSP, defined in measured amounts, gives no temperature for any of them.

Hot water does turn up in a rulebook written for brick. The Brick Industry Association (BIA), in Technical Note 20 on cleaning brickwork, writes: “Hot water can also be used in pressurized water cleaning. However, note that some pressure-washing equipment may not be capable of providing or using hot water.”

Two things keep that line off a roof. It was written for clay brickwork. And it describes pressurized water cleaning, the method that the shingle and metal documents rule out on their roofs.

Hot water and steam on pavers are a separate comparison, taken up in steam cleaning versus pressure washing pavers. How BIA's rulebook applies to clay brick on the ground is covered under paver cleaning materials. Whether any particular company heats its water is a question about that company's equipment, and the roof documents do not settle it either way.

If the documents do not ask the water to be hot, what are they relying on? Their answer is chemistry and time. ARMA's algae and moss bulletin says to “Apply with a sprayer and allow the solution to dwell on the roof surface for 15 to 20 minutes,” then rinse. The Metal Roofing Alliance lets its detergent solution stand 5 to 10 minutes. Each window belongs to its own document and its own roof.

That minutes-long wait is what the trade calls dwell time, defined on its own page, and the three-step sequence the bulletins publish is laid out on the method page under apply, dwell and rinse.

This is also the plain reason a soft wash is described by its solution rather than by its water. What a soft wash is, as a term, is set out under soft washing, defined. The water's job at the end, the rinse-down, is to carry the solution off, and why that final step stays in the published shingle and metal procedures is its own answer: the rinse after soft washing.