What it is
Sodium hypochlorite is the active chemistry in liquid bleach. In pressure-washing contexts, "SH" specifically means pool-grade 12.5% — the same product pool service companies use to chlorinate residential pools. It's the most cost-effective form of the chemistry for contractor use because it ships in 5-gallon jugs or 55-gallon drums and dilutes cleanly with water at the truck.
SH kills mold, mildew, algae, and Gloeocapsa magma at the cellular level by oxidizing cell walls. It's not a surfactant — it doesn't lift dirt by itself — so it's always paired with a separate surfactant chemical that helps the mix adhere to vertical surfaces long enough to work.
Working dilutions
- House wash (siding): 1.5-2% SH at the surface. From 12.5% pool-grade, that's roughly 1:5 to 1:7 by volume. Add surfactant per surfactant-manufacturer ratio.
- Roof wash (asphalt shingle): 3-4% SH at the surface. Roughly 1:2 to 1:3 from 12.5%. Heavier surfactant load for adherence on slope.
- Concrete pre-treatment: 1-1.5% SH. Light pre-spray to kill organics before the power wash pass.
- Heavy roof lichen: Spot treat with closer to 5-6% SH plus dwell time. Don't escalate the whole roof — just the lichen patches.
PPE — non-negotiable
- Chemical-resistant gloves (nitrile, 8-mil minimum) for mixing.
- Eye protection — splash goggles, not just safety glasses. SH droplets in the eye are a hospital trip.
- Respirator with acid-gas cartridges when mixing concentrated SH. The mixing vapors are harsher than the applied spray.
- Long sleeves and pants in chemical-resistant fabric. SH bleaches cotton on contact and irritates skin within minutes.
- Eye wash bottle on the truck. Always. $8 piece of insurance against a lost eye.
Surfactant
Surfactant is what makes the SH stay on the wall long enough to work. Without it, SH runs off vertical surfaces in 30-60 seconds — no dwell, no cleaning. Standard pressure-washing surfactants are sold by manufacturers like Power House, Apple Wash, Elemonator, and Roof Snot. Add at the surfactant-manufacturer-specified ratio (typically 4-8 oz per 5 gallons of mixed solution). More surfactant isn't better — too much foams excessively and complicates rinsing.
Plant protection
- Pre-water all plantings within 6 feet of the work zone, heavily, before applying any SH. Water dilutes SH on contact.
- Tarp delicate plants for roof work where over-spray is unavoidable.
- Apply on cloudy or cool conditions. Hot sun + SH = chemistry dries before rinsing, more plant damage.
- Post-rinse plantings within 5 minutes of finishing the application. Heavy water rinse, not a mist.
- Don't work on a windy day. Drift onto plantings 10-20 feet away is the #1 callback cause.
Cost reference
Pool-grade 12.5% SH costs $3-$5 per gallon at 55-gallon drum scale from a chemical distributor (drum minimum order typically). Retail 5-gallon jugs from Home Depot or a pool supply run $8-$15/gallon — fine for the first few months, expensive once volume scales. A typical residential house wash uses 5-10 gallons of 12.5% SH, so chemical cost per job lands at $15-$50 — 2-4% of revenue at typical pricing.
The chemistry is cheap. The acquisition cost is the lever.
Free account, free rendering, $1 per mailed postcard. SH costs about $30 per job; the postcard that booked the job costs about $1.
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