What is sodium hypochlorite?

Sodium hypochlorite is the active chemical in household bleach that pressure washing and soft washing contractors use to eliminate algae, mildew, moss, and other organic growth from roofs, siding, and exterior surfaces. It works by oxidizing and breaking down the cell walls of these organisms rather than relying on high-pressure spray alone.

In soft washing, sodium hypochlorite is diluted with water to a lower strength than what comes from the bottle, typically ranging from 500 to 2000 ppm (parts per million) depending on the surface type and the severity of contamination. Roofs and delicate materials usually call for weaker solutions, while heavily soiled concrete or masonry may tolerate higher concentrations. The chemical is often combined with surfactants and other additives to improve spread and penetration.

Proper rinsing after treatment is critical. Sodium hypochlorite that remains on the surface can continue to bleach and degrade certain materials, damage plants, and corrode metal components over time. Most soft washing providers follow a dwell time (letting the mix sit on the surface for 15 to 30 minutes) and then thoroughly rinse with low pressure or regular water to neutralize the bleach and prevent long-term damage. Understanding dilution ratios and rinse protocols is essential for any contractor using this chemical.