Soft washing

On a flyer or an estimate, the phrase can arrive as a compound, soft-wash cleaning, attached to a roof. 239 Exteriors uses that compound for its own roof cleaning; its roof flyer reads “Safe soft-wash cleaning.” The phrase names a method. It carries no pressure setting, no product name and no recipe inside it.

On an estimate the phrase may sit next to a roof type, tile or shingle. The definition does not change with the roof; what changes is the solution each material's documents call for, set out below. The separate matter of whether roof cleaning and roof washing are the same has its own answer.

SoftWash Systems, a soft washing equipment company, draws the line against pressure washing, “which uses high-pressure water to blast away dirt and grime,” and says soft washing “uses a low-pressure spray and specialized cleaning solutions.” Those two parts are one definition, not two options.

The full reasoning for why neither part is a soft wash on its own is at how soft washing works, and why the pressure itself stays low is answered at why roof cleaners use low pressure.

The solution part is not one recipe. For asphalt shingle, ARMA's bulletin names liquid household bleach and water, and GAF's bulletin adds TSP to bleach and water for its own shingles. For metal, the Metal Roofing Alliance names a mild detergent when water alone is not enough. Each recipe stays with the material it was written for.

No trade association or roofing maker document read for this page sets a pressure figure for soft washing. Where those documents print a pressure figure at all, it is written for a single material.

What the roofing documents do settle is the other side of the line. ARMA says not to use a power washer to clean algae from an asphalt roof and that high-pressure washing systems are likely to damage asphalt roofing, while its own procedure for algae discoloration uses a solution of liquid household bleach and water. The method in which force does the work is defined separately under pressure washing.