What is the mix order for SH and water?

Always add water to the tank first, then add SH. This dilutes the SH immediately on contact, preventing off-gassing and accidental splashing of concentrated SH. The mnemonic is: water, then SH.

Does surfactant change dwell time?

Yes. Surfactants slow the evaporation of SH off the surface, effectively extending usable dwell time by 10–20%. Elemonator-class surfactants (with a wetting agent and mild detergent) are more effective than generic Dawn-type surfactants for this purpose.

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SH Mix Calculator
Soft Wash Dilution & Dwell Time

Q: What SH concentration should I use for a house wash?

For vinyl siding house washing, industry standard is 0.5%–1.5% SH at the surface. Start with 1% (from 12.5% stock: 0.8 gal SH per 10 gal mix). Increase to 1.5% for heavy mold/algae. Always add a surfactant to improve dwell and coverage.

Q: What SH concentration is needed for roof washing?

Asphalt shingles: 3%–6% SH at the surface for effective gloeocapsa magma (black streaks/algae) removal. Use 4% as a starting point with a roof-specific surfactant like Roof Snot or an Elemonator-class product. Apply at low pressure (<100 PSI) with no-rinse dwell.

Q: Is powder-coated aluminum safe to soft wash?

With caution. Keep SH concentration ≤1% and dwell time ≤4 minutes. Rinse from bottom up immediately after dwell. High SH or extended dwell can chemically strip powder coating. Always test a small hidden area first.

Enter your stock SH concentration, target %, surface type, and mix volume. Get exact gallons, dwell time guidance, substrate safety warnings, and a printable PDF mix sheet for your truck.

House Wash1% target — vinyl siding

Roof Soft Wash4% target — asphalt shingle

Concrete2% target — flatwork

First freePDF download → email

Starting SH Concentration

Custom SH % (e.g. 8.25)

Surface Type & Target Concentration

Surface type

Target SH % at surface

Mix Volume & Surfactant

Total mix volume (gallons)

Surfactant

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gal SH

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gal water

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gal total

💰 Add cost estimate (optional) ▼

SH cost per gallon ($)

Surfactant cost per gallon ($)

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SH cost

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Surfactant

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Total chemical

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Your printable SH Mix Sheet PDF will arrive within 2 minutes. Want to document every mix for compliance?

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📋 What this proves on a Compliance Report

OSHA HazCom (29 CFR 1910.1200) and NPDES stormwater permits require a chemical usage log for every job. This mix sheet documents your SH concentration, dilution ratio, and surfactant — the three fields most commonly cited in compliance inspections. Keep a copy in your crew's SDS binder.

Safety & Compliance Pack (includes Chemical Log template) — $29 →

Frequently Asked Questions

What SH concentration should I use for a house wash? +

Industry standard for vinyl siding house washing is 0.5%–1.5% SH at the surface. Start with 1% (from 12.5% stock SH: approximately 0.8 gal SH per 10 gal total mix). Increase to 1.5% for heavy mold, algae, or shaded surfaces. Always add a surfactant to improve dwell time and coverage — Elemonator-class surfactants outperform generic dish soap for this purpose.

What SH concentration is needed for roof washing? +

Asphalt shingles: 3%–6% SH at the surface is needed to kill gloeocapsa magma (the bacteria causing black streaks). Start at 4% with a roof-specific surfactant. Apply at low pressure (<100 PSI) and allow a no-rinse dwell — rainfall rinses the dead biofilm over time. Never use high pressure on shingles; it removes granules and voids warranties.

What is the correct mix order for SH and water? +

Always add water first, then add SH. Adding concentrated SH to an empty tank creates dangerous off-gassing and splash risk. The mnemonic: "water, then SH." Fill your tank with water to the target volume, then add the calculated gallons of SH. Add surfactant last.

Is powder-coated aluminum safe to soft wash? +

With precautions. Keep SH concentration at or below 1% and dwell time under 4 minutes. Rinse from bottom up immediately after dwell before the surface dries. High SH concentrations or prolonged dwell will chemically strip powder coating — the damage is irreversible. Always test a small hidden area (back of a gutter, behind a downspout) before treating visible surfaces.

Does surfactant change the dwell time calculation? +

Yes. Surfactants slow the evaporation of SH off the surface, extending usable dwell time by 10–20%. Elemonator-class surfactants (which include a wetting agent and mild detergent) are more effective than generic surfactants for extending dwell because they help the SH penetrate organic growth rather than beading off. This calculator adjusts the dwell range upward slightly when a surfactant is selected.