Understanding SH Concentrations: From Store Bleach to 12.5%

Quick Answer

Household bleach from the grocery store is 3-6% sodium hypochlorite (SH) and contains additives that harm plants and leave residues. Professional soft washers use 10-12.5% SH, which is 2-4x stronger, cleaner-rinsing, and more cost-effective. Always verify SH concentration with a titration kit and never mix bleach with anything other than water and surfactants.

Key Takeaways

• Store bleach (3-6%) contains thickeners and additives that can damage plants and leave sticky residues
• Professional 12.5% SH is pure, cleaner-rinsing, and costs 75% less per active gallon
• A 1.5% working solution requires different amounts: 1:2 for 12.5% SH vs. 1:1 for 6% SH
• Always test SH strength with a titration kit—suppliers occasionally dilute product
• SH degrades 20-30% per month in hot weather; store in cool, dark places
• Use proper PPE: 12.5% SH causes severe chemical burns in seconds

Why SH Concentration Matters

The concentration of sodium hypochlorite determines everything about a soft wash operation: mix ratios, cost per job, effectiveness, and safety requirements. Using the wrong concentration assumption leads to failed cleanings or wasted money.

The hard reality: Most new contractors assume 12.5% SH from their supplier is actually 12.5%. In reality, supplier dilution is common in the industry. That “12.5%” being purchased might actually be 8% or 9%—which completely throws off mix ratios.

Household Bleach vs. Professional SH

Grocery Store Bleach (3-6% SH)

Household bleach brands like Clorox® or generic bleach typically contain 3-6% sodium hypochlorite, but the exact percentage varies by brand and region. More importantly, they contain additives that make them unsuitable for soft washing:

Problematic additives:

• Sodium hydroxide (lye): Raises pH to ~11, extremely harmful to vegetation
• Sodium polyacrylate: Thickening agent that leaves sticky residue on surfaces
• Fragrances: Completely unnecessary for cleaning, can trigger reactions
• Sodium chloride (salt): Already present as a byproduct, but added salt accelerates corrosion

Cost comparison:

• Household bleach: ~$0.12-0.20 per ounce of active SH
• 12.5% SH: ~$0.03-0.05 per ounce of active SH
• Paying 4-6x more for inferior product with additives

Professional 12.5% SH

Professional-grade sodium hypochlorite (often called “liquid pool chlorine” or “bulk SH”) comes in:

• 15-gallon carboys
• 55-gallon drums
• 275-gallon totes
• Bulk tanker delivery

Advantages:

• Pure product: No thickeners, fragrances, or unnecessary additives
• Cost-effective: 75-90% cheaper per active gallon
• Consistent strength: When verified, provides predictable results
• Better rinsing: No sticky residues left behind
• Less plant damage: Lower pH (typically 10-11) vs. household bleach (~13)

Understanding Dilution Ratios

The 1.5% House Wash Standard

The industry standard for vinyl siding cleaning is a 1.5% SH working solution. This provides enough cleaning power to kill mildew and algae while being relatively safe for plants when properly rinsed.

Critical point: The dilution ratio to achieve 1.5% depends entirely on starting concentration:

Starting SH	Dilution for 1.5% Working Solution	Ratio (SH:Water)
12.5%	1:7.3	~1:7
10.5%	1:6	1:6
6%	1:3	1:3
3%	1:1	1:1

Example calculation for 12.5% SH:

• Target: 1.5% working solution
• Formula: (Target ÷ Starting) = (1.5 ÷ 12.5) = 0.12 (12% of total volume)
• So for every 100 gallons: 12 gallons SH + 88 gallons water
• Simplified ratio: ~1:7 (1 gallon SH to 7 gallons water)

When adding surfactant: Most professionals add 8-16 oz of surfactant per gallon of SH. This displaces some water volume.

• Real-world mix for 100 gallons at 1.5%:
  • 12 gallons 12.5% SH
  • 1.5 gallons surfactant (192 oz at 16 oz/gal SH)
  • 86.5 gallons water

Roof Cleaning: Stronger Mixes

For asphalt shingle roof cleaning, contractors typically use 3-4% SH working solution to kill black streaks (Gloeocapsa magma).

Starting SH	Dilution for 3%	Dilution for 4%
12.5%	1:3.2 (~1:3)	1:2.1 (~1:2)
10.5%	1:2.5	1:1.6
6%	1:1	0.6:1 (60% SH)

Real-world roof mix (100 gallons, 3% target):

• 24 gallons 12.5% SH
• 3 gallons surfactant (16 oz/gal SH)
• 73 gallons water

Verifying SH Strength: Titration Kits

Every supplier will claim their SH is 12.5%. But in reality, it varies based on:

• Age since manufacture
• Storage temperature
• Supplier honesty (some dilute to increase profits)
• Transportation time in hot weather

How titration works: A titration kit uses a solution that reacts with SH to determine exact concentration:

1. Draw a small sample of SH
2. Add indicator drops until the color changes
3. Calculate concentration based on drops used

Cost: $25-50 for a basic kit

When to titrate:

• First delivery from new supplier (verify what you’re paying for)
• Monthly for stored SH (track degradation)
• When your mix isn’t working as expected
• After SH has sat in hot weather for 2+ weeks

SH Degradation Over Time

Sodium hypochlorite is unstable. It breaks down continuously, with heat accelerating decomposition.

Degradation rates:

• Ideal conditions (60°F, dark, sealed container): 2-3% strength loss per month
• Typical storage (75-85°F, outdoor shed): 15-25% strength loss per month
• Hot weather (90°F+): 30-50% strength loss per month

Storage best practices:

1. Temperature: Keep SH below 75°F whenever possible
2. Darkness: UV light accelerates breakdown—store in opaque containers
3. Ventilation: SH off-gasses; pressure builds in sealed containers
4. Freshness: Use within 30 days of delivery for optimal strength
5. Rotation: Use oldest stock first (FIFO)

Practical example: Purchasing 100 gallons of 12.5% SH on June 1st and storing it in an outdoor shed averaging 85°F. By August 1st (60 days later), it’s likely degraded to:

• Starting: 12.5%
• Day 30: ~9.4% (25% loss)
• Day 60: ~7.0% (44% total loss)

That means a “1.5% mix” is now actually ~0.84%—barely strong enough to clean.

Mixing Safety & Procedures

Proper PPE for 12.5% SH

Working with concentrated SH requires serious protection:

• Goggles: Chemical splash resistant (not safety glasses)
• Respirator: N95 minimum, preferably half-face with organic vapor cartridges
• Gloves: Nitrile or neoprene (latex degrades quickly)
• Suit: Chemical-resistant apron or full suit
• Boots: Rubber, not leather (SH destroys leather)

Why this matters: 12.5% SH causes irreversible eye damage in seconds and severe skin burns in under a minute.

Safe Mixing Order

Always mix chemicals in this specific order to prevent dangerous reactions:

1. Fill tank 50% with water (never start with chemicals)
2. Add measured SH while circulating
3. Top off with water to desired volume
4. Add surfactant last (it foams; adding last prevents overflow)
5. Circulate for 2-3 minutes to ensure thorough mixing

Never: - Mix chemicals in a bucket and pour into tank (inhaling fumes, splash risk) - Add SH to surfactant first (creates concentrated foam blob) - Mix different chemical batches in same tank without flushing - Leave SH in pump overnight (corrosion damage)

Real-World Mixing Examples

5-Gallon Bucket Mix (1.5% for Testing)

For small testing batches:

• 0.75 gallons 12.5% SH
• 10 oz surfactant
• 4.25 gallons water
• Total: ~5 gallons

50-Gallon Skid Mix (Standard House Wash)

For a typical 50-gallon soft wash system:

• 6 gallons 12.5% SH
• 96 oz (0.75 gallons) surfactant at 16 oz/gal
• 43.25 gallons water
• Total: 50 gallons

100-Gallon Tank Mix (Heavy-Duty)

For large jobs or stronger cleaning:

• 12 gallons 12.5% SH (for 1.5%)
• 1.5 gallons surfactant at 16 oz/gal
• 86.5 gallons water
• Total: 100 gallons

Cost Comparison: Why 12.5% Makes Sense

Scenario: 100 houses per year, averaging 50 gallons of mix per house

Using Household Bleach (6% SH)

Cost breakdown:

• Bleach: $4/gallon × 25 gallons = $100 per house
• Surfactant: $15/gallon × 0.75 gallons = $11.25 per house
• Total per house: $111.25
• Annual cost: $11,125

Using 12.5% SH

Cost breakdown:

• SH: $1.50/gallon × 6 gallons = $9 per house
• Surfactant: $15/gallon × 0.75 gallons = $11.25 per house
• Total per house: $20.25
• Annual cost: $2,025

Savings: $9,100 per year—enough to pay for a new skid system, better marketing, or higher profit margins.

Troubleshooting Mix Problems

“My Mix Isn’t Cleaning Anything”

Possible causes:

1. SH is degraded (titrate to verify)
2. Dwell time too short (minimum 10 minutes)
3. Too much dilution (check your math)
4. Heavy organic growth needs stronger mix (2-2.5% for gutters)

Fix: Titrate SH, increase to 2% working solution, extend dwell time to 15 minutes.

“Plants Are Turning Brown”

Possible causes:

1. Using household bleach with additives
2. Working concentration too strong (replace plant-sensitive areas)
3. No pre-wetting of plants
4. Insufficient post-rinse

Fix: Switch to pure 12.5% SH, reduce to 1% for plant-heavy areas, pre-wet and post-rinse thoroughly with water.

“Mix Foaming Over Tank”

Possible causes:

1. Adding surfactant before SH
2. Adding surfactant too fast
3. Using wrong surfactant type (some foam excessively)

Fix: Always add surfactant last, pour slowly, use defoamer if needed, switch to low-foam surfactant.

Related Articles

• Sodium Hypochlorite Complete Guide
• House Wash Mix Recipes
• Chemical Safety Essentials
• Surfactants Complete Guide

People Also Ask

Can I use pool shock powder instead of liquid SH?

Calcium hypochlorite (pool shock) is completely different from liquid SH. It:

• Leaves a white calcium residue that’s nearly impossible to rinse
• Requires mixing fresh daily (degrades faster than liquid)
• Can damage soft wash pumps (abrasive particles)
• Provides no cost advantage over liquid SH

Stick with liquid 12.5% SH for soft washing. Pool shock is great for pools, terrible for houses.

How long can I store mixed SH solution?

Once SH is diluted with water, it degrades rapidly:

• Day 1: Near full strength
• Day 3: ~20-30% strength loss
• Day 7: ~50% strength loss
• Day 14: Minimal remaining active SH

Best practice: Mix only what you'll use within 24-48 hours. For longer storage, keep SH concentrated (12.5%) and dilute fresh daily.

Is 12.5% SH worth it for part-timers?

Absolutely. Even at 10 houses per year:

• Household bleach cost: $1,112.50 annually
• 12.5% SH cost: $202.50 annually
• Savings: $910 (more than enough to cover basic equipment)

Plus, you’ll get better results with fewer callbacks—worth it at any volume.

Can I use household bleach in a pinch?

In an emergency, yes—but adjust your ratios. If you only have 6% bleach:

• Use 1:1 ratio (1 gallon bleach to 1 gallon water) for 1.5% working solution
• Expect stickier residues that may require additional rinsing
• Be extra careful around plants (household bleach has higher pH and more additives)

For regular work, the time spent dealing with callbacks and angry customers far outweighs the cost savings of switching to 12.5% SH.

How do I know if my SH has gone bad?

Signs of degraded SH: - Loss of chlorine smell (should have distinct pool smell) - Reduced cleaning effectiveness (mix isn't killing mildew) - Changed appearance (cloudy or discolored) - More than 60 days old in warm weather Only way to know for sure: Titration kit. Visual inspection and smell are unreliable—SH can smell strong but be weak, or smell weak but still have strength.