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DIY Soft Wash Guide

How to safely use bleach to kill mold on stone surfaces

Complete guide with dilution ratios and safety information

CRITICAL CHEMICAL SAFETY WARNING

Sodium hypochlorite (bleach) is a corrosive chemical that can cause severe burns and toxic fumes.

  • ALWAYS wear safety goggles and chemical-resistant gloves - bleach causes severe eye damage and skin burns
  • Work in well-ventilated areas - bleach fumes can cause respiratory irritation
  • NEVER mix bleach with ammonia, acids, or other chemicals - creates deadly toxic gases
  • Keep children and pets away from work area until completely dry
  • Protect all plants and landscaping - bleach runoff WILL kill vegetation
  • ALWAYS test on inconspicuous area first - bleach can permanently damage or discolor stone
  • Some stone types should NEVER be treated with bleach - see surface compatibility guide below
  • In case of eye contact: Flush with water for 15+ minutes and seek immediate medical attention
  • In case of skin contact: Rinse immediately with water for 15+ minutes and remove contaminated clothing

When in doubt about your stone type or proper dilution, consult a professional stone restoration specialist.

Understanding Sodium Hypochlorite (Bleach)

Know what you're working with before you start

What is Sodium Hypochlorite?

Sodium hypochlorite (SH) is the active ingredient in household bleach. It kills mold, algae, mildew, and bacteria by oxidizing organic matter. While effective, it's also a corrosive chemical that requires careful handling.

Common Bleach Concentrations

Household bleach comes in different strengths. Always check the label to determine the sodium hypochlorite percentage:

  • Regular Bleach: 5-6% sodium hypochlorite (most common)
  • Concentrated/Germicidal: 8.25% sodium hypochlorite (33% stronger)
  • Professional Grade: 10-12.5% sodium hypochlorite (requires dilution)

Reading the Label

Look for these terms on the label:

  • "Sodium Hypochlorite" percentage - This is what matters for dilution
  • "Active Ingredient" - Listed as sodium hypochlorite
  • "Concentrated" or "Regular Strength" - Indicates approximate percentage

Example: If label says "8.25% Sodium Hypochlorite", you have concentrated bleach that's stronger than regular 6% bleach. Adjust dilution ratios accordingly.

How Dilution Works

Diluting bleach reduces the sodium hypochlorite concentration to a safe level for your specific stone surface.

Basic Dilution Formula

Final SH% = (Starting SH%) × (Bleach Volume ÷ Total Volume)

Example: 1 part bleach + 4 parts water = 5 total parts
If using 6% bleach: 6% × (1÷5) = 1.2% final concentration

Simple Ratio Method

For most homeowners, it's easier to use part-based ratios:

  • 1:10 ratio = 1 cup bleach + 10 cups water
  • 1:5 ratio = 1 cup bleach + 5 cups water
  • 1:1 ratio = 1 cup bleach + 1 cup water (strong mix)

IMPORTANT MIXING RULE: Always add bleach TO water, never water to bleach. This prevents splashing and reduces fume exposure.

Stone Surface Compatibility Guide

Not all stone surfaces can be safely treated with bleach

SAFE FOR BLEACH (with proper dilution)

Concrete & Concrete Pavers

Recommended SH: 2-4% (final application strength)

Dilution: 1 part 6% bleach to 2-5 parts water

Dwell Time: 15-20 minutes

Notes: Most forgiving surface for bleach treatment. Good for driveways, walkways, patios.

Brick & Concrete Masonry

Recommended SH: 2-4% (final application strength)

Dilution: 1 part 6% bleach to 2-5 parts water

Dwell Time: 15-20 minutes

Notes: Similar to concrete. Watch for mortar damage on older brick.

USE WITH EXTREME CAUTION

Manufactured Stone Pavers

Recommended SH: 1-3% (start low!)

Dilution: 1 part 6% bleach to 5-10 parts water

Dwell Time: 10-15 minutes

CRITICAL: Colored pavers may fade. ALWAYS test first on hidden area.

Sandstone

Recommended SH: 1-2% (maximum)

Dilution: 1 part 6% bleach to 2-5 parts water

Dwell Time: 10-15 minutes maximum

CRITICAL: Very porous - rinse thoroughly. Can cause discoloration. Always test first.

Limestone

Recommended SH: <1% (very dilute only)

Dilution: 1 part 6% bleach to 10+ parts water

Dwell Time: 10 minutes maximum

CRITICAL: Can dissolve minerals and discolor. Consider alternative cleaners.

Granite (sealed)

Recommended SH: 0.5-1% (very dilute)

Dilution: 1 part 6% bleach to 10-15 parts water

Dwell Time: 5-10 minutes, rinse promptly

CRITICAL: Only if sealed. Can damage or strip sealant. Test first. Consider pH-neutral cleaner instead.

Travertine

Recommended SH: <0.5% (extremely dilute)

Dilution: 1 part 6% bleach to 15-20 parts water

Dwell Time: 5 minutes maximum

CRITICAL: Highly porous calcium-based stone. Can etch and discolor. Consider professional cleaning instead.

DO NOT USE BLEACH - WILL CAUSE DAMAGE

Marble

Why: Bleach causes permanent discoloration, etching, and structural damage to marble.

Alternative: pH-neutral stone cleaner only

Slate

Why: Bleach causes severe discoloration and can delaminate layers of slate.

Alternative: Water and mild detergent or specialized slate cleaner

Bluestone

Why: Bleach etches and permanently discolors bluestone surfaces.

Alternative: Low-pressure washing with water only

Flagstone

Why: Causes severe discoloration and weakens stone structure.

Alternative: Oxygen-based cleaners or low-pressure washing

Natural Stone Monuments/Headstones

Why: Sodium salt deposits cause irreversible breakdown of stone structure.

Alternative: Professional stone conservator only

Unsealed or Polished Granite

Why: Bleach will etch polished surfaces and stain unsealed granite.

Alternative: pH-neutral granite cleaner

Quick Dilution Reference Chart

Common dilution ratios for 6% household bleach

Target Final SH% Ratio (Bleach:Water) Example Mix Best For
0.5% (very weak) 1:11 1 cup bleach + 11 cups water Sensitive stone, test areas
1% (weak) 1:5 1 cup bleach + 5 cups water Limestone, delicate surfaces, light cleaning
2% (moderate) 1:2 1 cup bleach + 2 cups water Concrete, moderate mold, general cleaning
3% (strong) 1:1 1 cup bleach + 1 cup water Heavy mold on concrete, stubborn stains
4% (very strong) 2:1 2 cups bleach + 1 cup water Severe mold on concrete only

Converting for 8.25% Concentrated Bleach

If using concentrated 8.25% bleach instead of regular 6% bleach:

  • Use about 75% of the bleach amount (or add more water)
  • For 1% solution: Change from 1:5 ratio to approximately 1:7 ratio
  • For 2% solution: Change from 1:2 ratio to approximately 1:3 ratio

Formula: (6% ÷ 8.25%) = 0.73, so use 73% as much bleach or add proportionally more water

Required Equipment & Supplies

Essential Safety Equipment

  • Safety goggles or face shield - MANDATORY for eye protection
  • Chemical-resistant gloves - Nitrile or rubber, not latex
  • Long sleeves and pants - Protect skin from splashes
  • Closed-toe shoes - Protect feet from chemical spills
  • Respirator (optional) - For confined spaces or heavy fumes

Application Equipment

  • Pump sprayer - Garden pump sprayer (1-2 gallon capacity)
  • Stiff brush - For scrubbing stubborn mold
  • Garden hose - For rinsing
  • Plastic buckets - For mixing solutions
  • Plastic tarps - To cover plants and sensitive areas

Recommended Products (Amazon Affiliate Links)

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Pump Sprayer (1-2 Gallon)

Chemical-resistant pump sprayer perfect for applying bleach solutions to stone surfaces.

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Safety Goggles

Chemical splash goggles with full eye protection. Essential for preventing chemical burns to eyes.

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Safety Glasses

Protective safety glasses for eye protection from chemical splashes and debris.

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Nitrile Gloves

Chemical-resistant nitrile gloves. Protects hands from bleach burns and skin irritation.

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Step-by-Step Soft Washing Process

1

Preparation & Safety

  • Work on cool, overcast day (60-75°F ideal) - avoid direct hot sun
  • Check weather - don't apply before rain
  • Put on ALL safety equipment: goggles, gloves, long sleeves, closed-toe shoes
  • Thoroughly saturate all nearby plants with clean water
  • Cover sensitive plants with plastic tarps
  • Have helper available to rinse plants if needed
  • Keep children and pets indoors
2

Test on Inconspicuous Area

  • CRITICAL STEP - NEVER SKIP THIS
  • Choose hidden area (behind plants, under furniture, etc.)
  • Apply small amount of diluted solution
  • Wait 24 hours and check for discoloration, etching, or damage
  • If no damage appears, proceed with full application
  • If damage occurs, DO NOT PROCEED - consult professional
3

Mix Solution

  • Check bleach label for sodium hypochlorite percentage
  • Calculate proper dilution ratio for your stone type
  • ALWAYS add bleach TO water (never water to bleach)
  • Mix in well-ventilated outdoor area
  • For pump sprayer: mix directly in sprayer tank
  • Example: For 2% solution with 6% bleach, mix 1 cup bleach + 2 cups water
4

Apply Solution

  • Start from bottom and work upward (prevents streaking)
  • Apply evenly across surface with pump sprayer
  • Ensure complete coverage of mold/algae affected areas
  • Avoid over-application (creates excess runoff)
  • Watch for wind - don't let spray drift onto plants
  • If runoff occurs, have helper rinse plants immediately
5

Dwell Time

  • Concrete/Pavers: 15-20 minutes
  • Manufactured Stone: 10-15 minutes
  • Sandstone: Maximum 30 minutes
  • Limestone: Maximum 10 minutes
  • Watch for mold/algae to begin breaking down (color change)
  • NEVER let solution dry on surface - mist with water if drying
6

Scrub (if needed)

  • For embedded mold, use stiff brush during dwell time
  • Scrub in circular motions
  • Work solution into porous surfaces
  • Be gentle on delicate stone types
7

Rinse Thoroughly

  • Rinse with garden hose or low-pressure washer
  • Start from top, work downward
  • Ensure ALL bleach residue is removed
  • Multiple rinses recommended
  • No visible bleach residue or odor should remain
  • CRITICAL: Re-soak all nearby plants with clean water
  • Flush surrounding soil with water to dilute any runoff
8

Post-Treatment

  • Rinse plants again 24 hours later
  • Keep pets and children away until completely dry
  • Monitor plants for damage over next few days
  • Consider applying stone sealer after cleaning (wait 48 hours)
  • Clean and store all equipment properly

Critical: Protecting Plants & Landscaping

Bleach runoff WILL kill plants if not properly managed

Before Application

  • Saturate all plants thoroughly with water
  • Soak soil so plants can't absorb bleach
  • Water all foliage to create protective barrier
  • Cover delicate plants with plastic sheeting
  • Secure coverings against wind

During Application

  • Have helper spray plants with clean water
  • Immediately dilute any visible runoff
  • Monitor wind direction
  • Watch for overspray
  • Stop work if conditions worsen

After Application

  • Spray all plants with clean water
  • Multiple rinses recommended
  • Rinse again after 24 hours
  • Flush surrounding ground with water
  • Monitor plants for damage

When to Call a Professional

Unsure About Stone Type

If you're not certain what type of stone you have, professional assessment prevents costly damage.

Valuable/Historic Stone

For valuable, antique, or historic stone surfaces, always consult a professional stone conservator.

Large or Complex Areas

Large surface areas or complex landscapes with extensive plantings require professional equipment and expertise.

Professional soft washing ensures proper dilution, application, and protection for your property.

Learn About Our Professional Service

Not Sure You Want to DIY?

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