Mix the right soft wash batch

Work from the strength you want on the surface. The amount of sodium hypochlorite (SH) you need equals your total batch size times your target percent divided by your stock percent. The rest of the batch is water, and you add a surfactant at roughly 1% of the total volume so the mix clings and stays wet. For example, a 50-gallon batch at 3% from 12.5% SH is 12 gallons of SH, 38 gallons of water, and about 64 ounces of surfactant.

A common general house wash lands around 2 to 2.5% on the surface. Diluting 12.5% SH at roughly one part SH to four parts water gives about 2.5%, which is gentle enough for most siding while still killing algae and mildew. Always start lower on delicate surfaces and test a small area first.

Asphalt shingle roofs with heavy algae or black streaks typically need a stronger solution, around 3 to 5% on the surface. Roofs hold the solution longer and the staining is tougher, so the strength is higher than a house wash — but pre-wet and protect all surrounding plants and metal, and rinse thoroughly.

Square-foot pricing is the most common approach, generally in the range of $0.20 to $0.30 per square foot depending on surface, condition, and your market. Switch to the Job price tab above to estimate a job from the area and your rate.

A surfactant (sometimes called a "sticker" or elevated surfactant) is usually dosed at about 1% of the total batch volume — roughly 1 to 2 ounces per gallon depending on the product. It helps the solution dwell on vertical surfaces instead of running straight off. Always follow your specific product's label.