---
title: "Chem Ratio in Soft Washing: The Dilution That Matters |…"
description: "Definition of Chem Ratio: what it means in pressure washing and exterior cleaning, how it applies to Madison, WI home and commercial cleaning services."
url: https://www.thetotalwash.com/glossary/chem-ratio
source: https://www.thetotalwash.com/glossary/chem-ratio
generated: 2026-06-13T03:59:58.234Z
---

Chemicals & Detergents

# Chem Ratio

Chem ratio refers to the final dilution of cleaning chemistry at the surface — the percentage of active ingredient after the downstream injector, surfactant, and rinse water have all combined. For soft-wash work, the target ratio at the surface is typically 1-2% sodium hypochlorite for siding and 2-4% for roofs, down from a 12.5% concentrate in the bucket. Achieving the right ratio depends on injector flow rate, hose length, nozzle size, and pump pressure — and it is rarely a fixed number across all rigs.

## In depth

Professionals track chem ratio empirically: they know their rig's surface output from experience and verify with a pool-test strip or hardness tester on a sample surface before committing to a full job. Too rich a mix damages landscaping and wastes product; too dilute fails to kill organic growth and leaves streaks within weeks. Chem ratio discipline — buying a calibration kit, timing the mix at the surface, adjusting injector flow per job — is what separates a consistent, repeatable soft-wash operation from one that produces inconsistent results.

## How this shows up on our jobs

We log target chem ratio for every substrate (siding vs roof vs concrete), verify at the surface with test strips, and adjust mix based on how dirty the surface is and how hot the day is.

### Services where this matters

[House Washing](/residential/exterior-cleaning)[Roof Cleaning](/residential/exterior-cleaning)

## Related terms

[Sodium HypochloriteSodium hypochlorite (NaOCl) is the active ingredient in household bleach and the primary disinfectant used in professional soft washing. It is sold to exterior cleaners in 12.5% concentration (commonly called "SH" or "pool shock"), roughly twice the strength of consumer bleach. When applied in a properly mixed soft-wash solution, it kills algae, mold, mildew, lichen, and bacteria at the cellular level within minutes and breaks down into salt water and oxygen.](/glossary/sodium-hypochlorite)[DownstreamingDownstreaming is the technique of injecting soap or cleaning solution into the pressure washer's water line on the low-pressure side of the pump — downstream from the pump, hence the name. A chemical injector pulls detergent from a bucket through a siphon hose whenever a low-pressure (soap) nozzle is attached. When the technician swaps to a high-pressure nozzle, the injector automatically stops drawing chemical, allowing for a clean rinse without switching lines.](/glossary/downstreaming)[SurfactantA surfactant (short for "surface-active agent") is a chemical compound that lowers the surface tension of water so it can wet, spread, penetrate, and cling to a dirty surface instead of beading up and running off. In exterior cleaning, surfactants are blended with sodium hypochlorite and water to let the mix "stick" to vertical surfaces long enough for the bleach to kill organic growth at depth.](/glossary/surfactant)[Soft WashSoft washing is a low-pressure exterior cleaning method that uses biodegradable detergents and a controlled bleach solution to kill the algae, mold, mildew, and bacteria that cause staining — rather than scouring them off with brute force. A soft wash rig delivers cleaning fluid at roughly 60-200 PSI, comparable to a strong garden hose, which is safe on siding, shingles, painted surfaces, screens, and caulking. The chemistry does the work: the solution dwells on the surface, breaks down the organic growth at the cell level, and is then rinsed clean with fresh water.](/glossary/soft-wash)[Dwell TimeDwell time is the interval between applying a cleaning chemistry to a surface and rinsing it off. It is the single most misunderstood variable in exterior cleaning. Chemistry does not clean instantly; it needs time to break chemical bonds, kill organisms, or dissolve minerals. Too little dwell and the chemistry is wasted. Too much dwell — especially in direct sun — and the chemistry can damage the surface, bleach landscaping, or drive the stain deeper.](/glossary/dwell-time)

## Need this service in Madison?

The Total Wash Co. handles chem ratio and every other exterior cleaning service in the greater Madison, WI area. Get a free, no-obligation quote.

[Get a Free Quote](/instant-quote)[Call (608) 360-5818](tel:+16083605818)

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