Sodium Hypochlorite (SH) Guide: Pressure Washing's Primary Chemical

Key Takeaways

• SH is concentrated bleach — 10–12.5%, not household-grade
• Mix by percentage, not ratio — A 1:10 ratio is not 10% (math matters)
• Surfactant is mandatory — Skip it and chemicals waste and work suffers
• PPE non-negotiable — Chemical burns cause permanent damage
• 3% is your ceiling — Stronger concentrations risk surface damage

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What is Sodium Hypochlorite?

The Basics

Sodium hypochlorite (NaOCl) is concentrated bleach at 10–12.5% strength, sourced from pool suppliers and chemical distributors. Household bleach from the grocery store is 3–6% and unsuitable for professional work.

What it does:

• Oxidizes organic matter, killing algae, mold, mildew, bacteria, and viruses on contact
• Breaks down to salt and water (environmentally safe after degradation)
• Works rapidly—minutes, not hours
• Tackles nearly all organic stains

Why professionals use it:

• Kills growth fast on surfaces
• Cost-effective: $15–25 per gallon yields 100+ gallons of working solution
• Widely available from pool supply stores and chemical distributors
• Proven track record across industries

Professional SH vs. Household Bleach

For complete details on mixing and application methods, check out our house wash mix recipes guide.

10–12.5% SH from pool supply:

• Concentrated. One gallon makes 10–12 gallons of working solution
• Pure bleach, no additives
• Consistent quality when sourced fresh
• Cost: $0.15–0.25 per gallon of working solution

3–6% household bleach:

• Already diluted and cannot be concentrated further
• Contains additives—thickeners clog equipment, added scents serve no purpose
• Quality varies based on shelf age
• Cost: $1–2 per gallon of working solution

Don’t use household bleach. Equipment degradation occurs from additive buildup. Effectiveness suffers. Per-gallon costs exceed professional-grade alternatives.

Bottom line: Buy 10–12.5% SH from a pool supplier. Equipment lasts longer. Costs stay low.

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Mixing Calculations

The Percentage vs. Ratio Problem

Percentage and ratio are not interchangeable. Many professionals confuse them.

1:10 ratio = 1 part chemical, 10 parts water = 11 parts total = 9.1% strength (not 10%)

1% actual strength = 1 gallon SH per 100 gallons total volume

These aren’t equivalent. Precision in percentage ensures consistency.

The formula:

SH Percentage = (SH volume ÷ Total volume) × 100

Quick shortcuts:

• Want 1% final? → 1 gallon SH per 100 gallons total
• Want 1.5%? → 1.5 gallons SH per 100 gallons total
• Want 2%? → 2 gallons SH per 100 gallons total

Mixes for Professional Work

General Cleaning (1% SH):

• House washing, mild growth, general dirt removal
• 1 gallon SH + 99 gallons water = 100 gallons total

Heavy Growth (1.5% SH):

• Stubborn algae and organic stains
• 1.5 gallons SH + 98.5 gallons water = 100 gallons total

Roof Cleaning (2% SH):

• Black algae streaks and heavy buildup on shingles
• 2 gallons SH + 98 gallons water = 100 gallons total

Delicate Surfaces or Testing (0.5% SH):

• Painted wood and unknown surfaces
• 0.5 gallons SH + 99.5 gallons water = 100 gallons total

Maximum strength: 3% SH. Damage risk increases dramatically above this threshold. Most jobs succeed with 1–2%.

Small Batches (5-Gallon Tank)

For 1% mix:

• SH: 0.05 gallons (about 6–7 ounces, roughly 3/4 cup)
• Water: fill the rest
• Surfactant: add 5–10 ounces

For 50-gallon batches (driveway, patio):

• SH: 0.75 gallons (approximately 3/4 gallon)
• Water: fill to 50 gallons
• Surfactant: 100–150 ounces (about 1 gallon)

Conversion reference:

• 1 cup = 8 ounces
• 1 pint = 16 ounces
• 1 quart = 32 ounces
• 1 gallon = 128 ounces

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Surfactants: The Critical Component

Why Surfactant Matters

Surfactant is the difference between effective cleaning and wasted time.

What surfactant accomplishes:

• Makes SH stick to surfaces instead of beading up and running off
• Helps SH soak into pores and crevices
• Keeps surfaces wet longer
• Breaks surface tension for better dirt lift
• Provides visual coverage indicator (foam)

Without surfactant:

• Chemical runs down immediately
• Spotty, uneven coverage
• Expensive SH wasted
• Longer dwell time required
• Poor results

With surfactant:

• Sticks to vertical surfaces
• Even coverage across area
• Chemical stays wet longer
• Better cleaning in less time

Types and Selection

Commercial surfactants:

• Citrus-based (most common, excellent performance)
• Cherry-scented (masks bleach odor)
• Foaming types (visual coverage indicator)
• Cost: $20–40 per gallon

DIY options:

• Dawn dish soap (works adequately)
• Laundry detergent (budget choice)
• Palmolive (useful for oily residue)

Usage rates:

• Professional surfactant: 1–2 ounces per gallon of mix
• Dish soap: 2–3 ounces per gallon of mix
• Laundry detergent: 1–2 ounces per gallon of mix

Don’t overuse. Excess surfactant leaves sticky residue, attracts dirt, and complicates rinsing.

Mixing Order and Safety

The correct sequence:

1. Fill tank with water first
2. Add SH to water (never the reverse)
3. Add surfactant last
4. Mix gently—no bubble bath needed
5. Use same day if possible (SH loses potency over time)

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Application Methods

Downstream Injector

Water flow sucks chemical from a tank behind the pump. Chemicals mix automatically. Typical ratio is 10:1 to 15:1 (10–15 gallons water per gallon chemical).

Best for:

• Speed and efficiency
• Large flat surfaces
• Driveways, patios, concrete
• Consistent application

Limitations:

• Vertical surfaces (chemical needs to cling)
• Delicate surfaces (reduced control)
• Precision work

Pump Sprayer

You pump pressure into a tank and spray chemical directly. No mixing on the fly. Direct control over application.

Best for:

• Houses and siding
• Fences and decks
• Vertical surfaces (chemical clings better)
• Delicate surfaces
• Chemical efficiency

Limitations:

• Large open areas (slower process)
• Arm fatigue on extended use
• Multiple refills for large jobs

Selecting Your Method

Downstream injector for:

• Driveways, patios, flatwork
• Large areas prioritizing speed
• Heavy growth situations

Pump sprayer for:

• Houses and buildings
• Fences, decks
• Delicate materials
• Work requiring precision

Most professionals use both methods—pump sprayer for vertical work, injector for horizontal surfaces.

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Safety Considerations

Personal Protective Equipment

Every time you handle SH, wear:

• Eye protection — Goggles or face shield (one splash causes blindness)
• Gloves — Chemical-resistant (nitrile or rubber)
• Respirator — N95 minimum; P100 cartridges for regular use
• Long sleeves — Chemical-resistant or quick-dry material
• Long pants — No shorts when mixing
• Boots — Closed-toe, chemical-resistant preferred

Why this matters:

• SH burns skin on contact
• Eye splash causes permanent vision damage
• Fumes irritate and damage lungs
• SH bleaches and degrades clothing

Handling and Storage

When mixing or applying:

• Work outdoors or in well-ventilated areas
• Never mix SH with anything acidic (creates chlorine gas)
• Label everything clearly
• Keep baking soda or sodium thiosulfate nearby (neutralizes spills)

Storage best practices:

• Cool, dark place (heat and light degrade SH)
• Plastic containers only (SH corrodes metal)
• Away from acids (vinegar, toilet bowl cleaner, muriatic acid)
• Locked if children are present
• Check dates—SH lasts 6–12 months; potency declines after

In-vehicle storage:

• Secure containers to prevent spillage
• Ventilate the vehicle properly
• Never store SH and acid together
• Use plastic tubs under tanks to catch leaks

Environmental Protection

When protecting landscaping:

• Cover plants with plastic sheeting
• Wet plants before covering (reduces burn risk)
• Rinse immediately if chemical contacts plants
• Avoid spray drift toward streams or ponds
• Prevent runoff toward storm drains when possible

Gentler alternatives for sensitive areas:

• Peroxide-based cleaners for sensitive plants
• Still protect and rinse—lower risk than SH

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Where SH Works and Where It Doesn’t

Excellent Results on Organic Growth

• Vinyl siding (algae and mildew vanish)
• Roof shingles (black algae streaks)
• Concrete (organic stains)
• Wood (gray wood, soft wash method)
• Fences (vinyl and wood)
• Brick and masonry (organic growth)

Good Results with Caution

• Stucco (may need brushing)
• Aluminum siding
• Composite decking (mold and mildew)
• Painted surfaces (test first—may remove paint)
• Delicate wood (soft wash only—may raise grain)
• Natural stone (some types bleach-sensitive)
• Windows (protects seals)

What SH Cannot Remove

• Rust (requires oxalic acid)
• Oil or grease (requires degreaser)
• Efflorescence (requires acid cleaner)
• Paint buildup
• Mineral deposits and hard water stains

SH kills organic growth exclusively. For other stains, use appropriate chemistry. See the stain removal guide for specifics.

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Troubleshooting

SH Not Working

Old chemical:

• SH loses potency over time
• Smell test: should smell strongly of chlorine
• Solution: buy fresh from suppliers with high turnover

Mix too weak:

• Check your dilution math
• Increase percentage up to 3% maximum

Dried too fast:

• SH evaporated before working
• Add more surfactant or mist surface to keep wet longer

Wrong chemical for the stain:

• Stain isn’t organic
• Rust, oil, or minerals require different chemicals

Surface Damage

Applied too strong:

• Percentage too high
• Use 1% or lower next time

High pressure post-application:

• Pressure too aggressive right after SH
• Use soft wash (under 1,200 PSI), maintain distance

Left on too long:

• SH sat longer than 30 minutes
• Rinse after 15–30 minutes maximum

Delicate surface:

• Surface doesn’t tolerate SH well
• Test first in inconspicuous areas, or use pH-neutral cleaner

Plant Damage

Why it happened:

• Chemical touched plants without protection
• No immediate rinsing
• Drift from overspray

Next time:

• Cover all plants without exception
• Wet them before covering
• Rinse immediately if chemical contacts
• Use gentler peroxide-based cleaner in sensitive areas

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Alternatives When Needed

Peroxide-based cleaners:

• Use near sensitive landscaping
• Gentler and plant-safe
• More expensive, slower, less effective on heavy growth

Vinegar:

• Light mildew, delicate surfaces
• Cheap and available
• Weak and limited effectiveness

Specialty cleaners:

• Formulated for specific stains
• Expensive and single-purpose

For most pressure washing work, SH is the right tool. Use alternatives when they specifically fit the job—not to save money.

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The Economics

What SH costs:

• Purchase: $15–25 per gallon (10–12.5%)
• Yield: 100–150 gallons of 1% working solution
• Per gallon: $0.10–0.25 in working solution

Per job cost:

• House wash (5–10 gallons mix): $0.50–2.50 in SH
• Driveway (20–50 gallons): $2–12.50 in SH
• Roof (30–60 gallons): $3–15 in SH

Add surfactant: ($20–40 per gallon, 1–2 oz per gallon mix)

• House: +$1.50–3
• Driveway: +$3–8
• Roof: +$4–10

Total chemical cost per job: $2–8 (house), $5–20 (driveway), $7–25 (roof)

Chemical cost represents a tiny fraction of job price. Don’t cut corners on chemicals—you’ll waste time, use more product, and get worse results.

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Five Critical Practices

1. Buy in Bulk

Lower cost ($12–15/gallon vs. $20–25 retail). Always maintain supply. Find local chemical distributors or pool supply stores serving contractors. Buy 5–15 gallons at a time. Ask about turnover—you want fresh product.

2. Mix Fresh Daily

SH degrades over time. Mix in the morning, use the same day. Label the tank with date and strength. Don’t leave old mix in the tank. Dilute it heavily and dispose properly.

3. Test Before You Commit

Small patch (2×2 feet) in an inconspicuous area. Wait 10–15 minutes. Watch for color change, etching, or adverse reactions. If something looks wrong, stop and use gentler approach.

4. Know Your Percentages

• 0.5%: delicate surfaces, testing
• 1%: general cleaning
• 1.5%: heavy growth
• 2%: roofs, stubborn stains
• 3%: maximum, rarely needed

Start low. Increase if necessary. Multiple light applications beat one heavy one.

5. Treat It With Respect

SH kills organic matter. It’s corrosive. Fumes are toxic. Never mix with acid. Always ventilate. Always wear PPE. Label everything. Store properly. Dispose responsibly.

It’s a powerful tool. Use it like one.

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Next Steps

• Chemical Safety Guide
• Surfactants Guide
• House Wash Mix Recipes
• Pressure Washing Safety