Chemical Ratio & Downstream Engine

Universal Pressure Washing Dilution Calculator: Batch & Downstream Mixes

Guessing chemical ratios leads to burned plants, etched concrete, or surfaces that just don't get clean. This free dilution calculator tells you exactly how much raw chemical and water to mix in your bucket to hit the perfect percentage at the wand tip, whether you are using bleach (SH), heavy degreasers, or wood brighteners.

The Downstream Injector Math Problem

If you drop a standard downstream injector into straight 12.5% commercial SH or an industrial degreaser, you aren't hitting the surface at full strength. A standard 10:1 injector dilutes your chemical with 10 parts water. This means your final spray is roughly 1/10th of the bucket strength.

Target Strengths by Surface & Chemical

Applying the correct strength prevents costly damage and eliminates wasted product:

  • House Wash (SH): 0.75% to 1.0% at the tip.
  • Roof Wash (SH): 3.0% to 4.0% at the tip.
  • Heavy Degreaser (Oil Stains): 20% to 30% at the tip.
  • Wood Brightener (Oxalic Acid): Follow manufacturer oz/gallon ratios, applied via pump sprayer.

Interactive Dilution & Batch Calculator

Live Calculation
Helper: Vinyl Siding = 0.8%, Roofs = 3.5%
Mixing Recipe & Batch Proportions
1. Raw Chemical Required
4.00 Gallons
12.5% Commercial Sodium Hypochlorite
2. Clean Water to Add
1.00 Gallons
Fill remainder of 5.0 gallon bucket
3. Surfactant (Soap)
4.0 oz
1 oz per gallon of raw SH
Chemical Safety Precaution:

Always wear PPE (respirator, chemical-resistant gloves, and eye protection). Never mix SH with acids or ammonia—toxic chlorine gas will form.

Outputs auto-recalculate on every keystroke. Prints formatted 1-page batch sheet.

Chemical Dilution & Downstream FAQs

Why is my degreaser not lifting oil when I downstream it?

Most heavy degreasers require a 20% to 30% concentration to lift set-in oil. A standard 10:1 downstream injector dilutes pure degreaser down to ~10% at the tip. You must apply degreaser directly with a pump sprayer.

Can I run raw chemicals through my pressure washer pump?

Never run SH, acids, or harsh degreasers through your high-pressure pump. Always draw them after the pump using a downstream injector, or use a dedicated low-pressure 12V soft wash pump.

Why does my downstream injector stop pulling soap when I use a long hose?

Downstream injectors rely on the Venturi effect, which requires low back-pressure. If you run more than 150 feet of high-pressure hose, or if you are spraying 2-stories up, the back-pressure defeats the vacuum, and it stops drawing chemical. Move the injector closer to the gun.

Can I just use household bleach (5.25%) instead of commercial SH (12.5%)?

Yes, but your math changes drastically. Because household bleach is less than half the strength, a standard downstream injector will dilute it down to roughly 0.5% at the tip. This is often too weak to clean heavy algae on siding without doing a secondary batch mix.

How much surfactant (soap) do I actually need to add?

The industry standard is typically 1 ounce of dedicated pressure washing surfactant per 1 gallon of raw SH in your batch. Using too much soap causes excessive suds that take hours to rinse off, while too little means your SH will run off the siding before it can kill the algae.

* Chemical Safety & Mix Proportions Notice: Dilution ratios are calculated based on standard pressure washing volumetric formulas. Always test chemical mixes on an inconspicuous test spot before broad application. Pre-soak surrounding plants, grass, and sensitive hardscapes with clean water before and after chemical application.