Sodium hypochlorite

The Brick Industry Association states the relationship outright in Technical Note 20, on cleaning brickwork: “Sodium hypochlorite, the active ingredient in household bleaches, can also be used to remove mild vanadium stains.” The sentence is about brick; its middle clause is why the chemical name and the household one travel together.

The Asphalt Roofing Manufacturers Association (ARMA) writes the two as one phrase in its technical bulletin on algae discoloration, which says the stain may be lightened by applying “a solution of liquid household bleach (sodium hypochlorite) and water.” ARMA's verb is lightened; whether the wash kills the growth or only lifts it is the question behind does soft washing kill the algae or just remove it.

A bleach maker's safety data sheets describe the product in the bottle, not anything mixed for a roof. The Clorox Company's 2019 sheet for Clorox Disinfecting Bleach2 classes the undiluted product as corrosive, with the hazard statement “Causes severe skin burns and eye damage,” and the odor and pet lines from the same maker's sheets are quoted in does soft washing smell and should pets stay inside during roof cleaning.

Whether a particular bleach product carries an EPA pesticide registration is a matter of that product's own label, as biocide explains. What the roofing documents put in a wash, and the mixing question ARMA leaves to each shingle maker's own directions, is laid out under what is in a soft wash solution.

Each trade document that calls for bleach ties it to one material and to named stains or growth, and none of those uses is written for another surface.

• Asphalt shingle: ARMA's bleach and water solution for algae discoloration, with ARMA's caveat that shingle makers' mixing directions may differ.
• GAF shingles: GAF's own mixture of water, bleach and TSP (“or acceptable phosphate-free substitute,” in GAF's words), left on the roof for up to 20 minutes and rinsed with low-pressure water.
• Metal roofs: the Metal Roofing Alliance's tips call for a garden hose first and then a mild detergent; bleach is not named on the tips page read for this entry.
• Concrete pavers: for “Leaf, wood rot, or tobacco stains,” the Interlocking Concrete Pavement Institute's Tech Spec 5 says to “apply household bleach and scrub with a stiff bristled brush.”
• Natural stone: the Natural Stone Institute's care guide has outdoor pool, patio and hot tub areas flushed with clear water, then a mild bleach solution used against algae or moss.

Other lines fence it off from what sits beside the work, starting with glass. Solutions containing sodium hypochlorite, bleach first among them, head the National Glass Association's “examples of some materials that may cause harm” to laminated glass, and PGT describes its WinGuard hurricane windows and doors as made with laminated glass, so keeping a sodium hypochlorite roof solution, vapors included, away from impact glass is a technical requirement of the trade. The glass itself is defined at laminated glass.

Plants are next. ARMA asks for “proper precautions to protect landscaping and surrounding areas from the chlorine bleach solution,” and GAF, for its own mixture, adds: “Be sure to protect any shrubs below.” What that means for a planting bed under a roof line is worked through in does roof cleaning hurt plants, and the paver, stone and brick side sits with will bleach hurt my pavers.