What is in a soft wash solution?

Soft washing leans on its cleaning solution rather than on pressure, so the fair question about the method is what that solution contains.

The honest starting point is that “soft wash solution” is a category, not a product with a published recipe. No trade association or roofing maker read for this answer publishes a formula under that name. None publishes a sodium hypochlorite percentage for soft washing, and none publishes a specification for a surfactant.

What is in print is narrower and more useful: four publishers, each behind one roofing material, each naming the ingredients they will accept on that roof. Set side by side, they answer the question roof by roof.

Each row below is one publisher's own list for one material. None of them was written as a general recipe.

ARMA's technical bulletin puts it this way: “Discoloration may be lightened by applying a solution of liquid household bleach (sodium hypochlorite) and water.” GAF's bulletin gives its mixture with a dwell time of up to 20 minutes and a low-pressure rinse. The Metal Roofing Alliance names mild laundry detergent, car washing soap or dish soap. Eagle gives a limit rather than a mix: as diluted as possible and compatible with concrete.

ARMA's second document on algae and moss does print a 50:50 mix of laundry strength liquid chlorine bleach and water for asphalt shingle, while its technical bulletin leaves the mix to the shingle maker. How those two ARMA documents differ, and why no ratio is printed as a rule, is set out under what the bulletins tell a roof cleaner to do instead.

The pattern in the table is the answer's main point: each ingredient list is tied to the roof its publisher makes or represents, and none of them offers itself for another roof.

ARMA writes that fence into its own bulletin: “Other cleaning chemicals or methods should not be used without the approval of the shingle manufacturer.” Eagle builds a different fence for concrete tile, warning that some products can affect the tile's pH or even etch the surface. The reasons a mix made for one roof does not carry over to another are argued under whether tile and shingle can be cleaned with the same solution, and the makers' cleaning limits sit together in the tile, shingle and metal comparison on the roof cleaning page.

So the question that matters for a given house is not what a soft wash solution contains in general. It is which roof it is going on, and what that roof's maker allows.

GAF's bulletin is the only one of the four to name a third ingredient. Its mixture calls for “1 cup (236 mL) of TSP (Tri-Sodium Phosphate-or acceptable phosphate-free substitute)” alongside the water and bleach.

Two things follow from GAF's own wording. TSP is GAF's ingredient for GAF shingles, not a standard part of every roof mix. And the word phosphate-free, in a roof context, is GAF's allowance for an alternative to trisodium phosphate; none of the roofing documents quoted here requires a phosphate-free product. Neither line says anything about what a particular cleaner mixes.

Two of the four lists name bleach, and bleach is the ingredient with a published consequence below the roof. The National Glass Association's Glass Technical Paper FB01-00 writes: “The plastic interlayer in laminated glass is generally exposed around the periphery of the window glass; cleaning fluids and their vapors must be kept away from this area.”

The same paper tells cleaners not to use anything corrosive on laminated glass, and its named examples include “Bleach (or other solutions containing sodium hypochlorite)”. Impact windows are built with laminated glass. Where a roof solution contains sodium hypochlorite, NGA's rule for that glass becomes a requirement of the roof wash itself: the solution and its vapors stay off the windows below. What an exterior cleaner has to know about impact, Low-E and tempered glass is covered under the glass types an exterior cleaner must know.