Softwash Batch Mix Calculator

Professionally calculate water, Sodium Hypochlorite (SH), and surfactant ratios for your soft washing mix tank.

Batch Mix Composition

Quick Reference: Common Mixes based on 12.5% Source SH

Application	Target %	Ratio (Water:SH)	SH per 50 Gal
Vinyl Siding (Light)	0.8% – 1.0%	12:1	~4 Gal
Vinyl Siding (Heavy)	1.5%	7:1	~6 Gal
Stucco / Brick	2.5% – 3.0%	3:1	~10-12 Gal
Roof (Asphalt Shingles)	3.0% – 4.0%	2:1	~12-16 Gal
Concrete Flatwork	3.0% – 4.0%	2:1	~12-16 Gal

What is a Softwash Batch Mix Calculator?

A softwash batch mix calculator is an essential tool for professional exterior cleaners who utilize a “batch mixing” system rather than a downstream injector or proportioner (like a softwash metering valve). In batch mixing, the cleaning solution—comprising water, sodium hypochlorite (SH), and surfactant—is pre-mixed in a dedicated holding tank before being pumped onto the surface.

Precise calculation is critical because different surfaces require drastically different concentrations of bleach to clean effectively without causing damage. For instance, cleaning a sensitive painted surface might require a 1% mix, while a heavily soiled asphalt shingle roof might need a 4% mix. This calculator eliminates the guesswork, ensuring you mix the exact proportions needed for your specific softwash batch mix calculator requirements.

Using a calculator helps prevent wasted chemicals, protects landscaping from overly hot mixes, and ensures enough “kill power” to remove algae (Gloeocapsa Magma) and mildew in one pass.

Softwash Batch Mix Formula and Mathematical Explanation

The math behind soft washing is based on dilution ratios. The core objective is to determine how much concentrated bleach (Source SH) is needed to achieve a desired lower concentration (Target SH) within a fixed volume of liquid (Batch Size).

The Core Formula

SH Gallons Needed = (Target Strength % / Source Strength %) × Total Batch Size

Once the volume of SH is determined, we calculate the surfactant volume, and the rest is water.

Variable Definitions for Softwash Calculation

Variable	Meaning	Unit	Typical Range
Target Strength	Final percentage of SH on the wall/roof	%	1.0% (Siding) to 6.0% (Tile Roof)
Source Strength	Concentration of bleach in your supply tank	%	10% (Pool) or 12.5% (Industrial)
Batch Size	Total volume of mix to create	Gallons	25 to 100 Gallons
Surfactant Rate	Amount of soap to help mix stick to vertical surfaces	oz/gal	1 to 3 oz per gallon

Practical Examples (Real-World Use Cases)

Example 1: Residential Roof Cleaning

Scenario: You need to clean a steep asphalt shingle roof with heavy algae growth. You have a 50-gallon batch tank and 12.5% industrial SH. You want a “hot” mix of 4% to ensure the moss dies instantly.

• Target: 4.0%
• Source: 12.5%
• Batch Size: 50 Gallons

Calculation: (4.0 / 12.5) × 50 = 16 Gallons of SH.
You would add roughly 50 oz of surfactant (at 1 oz/gal).
The remaining volume (approx 33.6 gallons) would be water.

Example 2: Vinyl Siding House Wash

Scenario: You are washing a two-story home with vinyl siding. A 4% mix would be too strong and might oxidize the paint or kill plants. You need a mild 1% mix. You are using a smaller 25-gallon buffer tank.

• Target: 1.0%
• Source: 12.5%
• Batch Size: 25 Gallons

Calculation: (1.0 / 12.5) × 25 = 2 Gallons of SH.
This saves you money on chemicals while still providing enough cleaning power for green algae. The rest of the 23 gallons is water and soap.

How to Use This Softwash Batch Mix Calculator

1. Enter Total Batch Size: Input the size of the tank you are filling or the total amount of fluid you wish to make (e.g., 50 gallons).
2. Set Target Strength: Determine what the surface requires. Use 1% for house washing and 3-4% for roof cleaning.
3. Select Source Strength: Check the label on your bleach drum. Most pressure washing suppliers provide 12.5%. If buying from a pool store, it may be 10%.
4. Add Surfactant Rate: Enter how many ounces of soap you want per gallon of mix. This helps the solution cling to roofs and walls.
5. Review Results: The calculator instantly shows how much SH, water, and soap to pour into your tank.

Key Factors That Affect Softwash Results

While the softwash batch mix calculator gives you the mathematical ratios, several physical factors affect the real-world performance of your mix.

• SH Degradation: Sodium Hypochlorite degrades over time, especially in heat and sunlight. “12.5%” bleach bought 3 months ago might only test at 9% today. Always assume older bleach is weaker.
• Temperature: Chemical reactions speed up in heat. A 3% mix on a hot sunny day acts more aggressively than a 3% mix on a cold morning (Active Arrhenius equation).
• Surface Porosity: Porous surfaces like brick and concrete absorb mix, requiring higher volumes and sometimes higher concentrations compared to non-porous vinyl.
• Organic Load: Thick moss requires more chemical contact time and volume than light green algae dust.
• Surfactant Type: Some surfactants (like Lauramine Oxide) create thicker foam, increasing dwell time on vertical surfaces, which effectively boosts the cleaning power without adding more bleach.
• Plant Protection: Higher concentrations increase the risk of plant damage. Always pre-wet and post-rinse vegetation when using stronger batch mixes.

Frequently Asked Questions (FAQ)

What is the best mix ratio for roof cleaning?

For asphalt shingle roofs, a mix between 3% and 4% is standard. If using 12.5% SH, this is roughly a 3:1 ratio (3 parts water to 1 part SH). Terra cotta or tile roofs may require up to 5-6%.

Can I use household bleach for soft washing?

Yes, but it is less efficient. Household bleach is usually 5-8.25%. You will need to buy almost double the volume compared to industrial 12.5% SH to achieve the same softwash batch mix strength.

Why do I need surfactant?

Surfactant reduces surface tension, allowing the mix to spread evenly and “cling” to slopes. Without it, the bleach runs off the roof too quickly to kill the algae effectively.

Is batch mixing better than downstream injection?

Batch mixing allows for much stronger mixes (up to 50% SH or more) required for roofs. Downstream injectors typically cap out at around 1-1.5% SH, which is great for siding but often too weak for dirty roofs.

How do I neutralize the bleach afterward?

Bleach breaks down into salt and water naturally, but using a commercial neutralizer (like Bleach Neutralizer) on equipment and plants is recommended to stop corrosion and prevent leaf burn.

What if my batch mix is too strong?

If you accidentally mix it too hot, simply dilute it by adding more water to the tank. This is the advantage of a batch mix system; it is easily adjustable.

Does temperature affect my SH strength?

Yes. Store your SH in a cool, dark place. At 90°F, SH degrades significantly faster than at 60°F.

Can I mix other chemicals with SH?

NEVER mix acids (like window cleaner or rust remover) with Sodium Hypochlorite. This creates deadly chlorine gas. Only mix water, SH, and compatible surfactants.