In exterior cleaning and soft washing, "SH" stands for Sodium Hypochlorite. It is the active chemical ingredient in household laundry bleach and liquid pool shock. In sodium hypochlorite pressure washing, SH kills green algae, mold, and black roof streaks right at the root. You don't have to blast surfaces with gouging high pressure. Bleach kills spores. Pressure cleans dirt. Dilution is everything. Once you understand what is SH in pressure washing and master your ratios, you can safely wash a two-story house in under an hour. Best of all, your ladder stays on the truck.
The biggest beginner mistake I see on jobs is spraying too hot of a mix and scorching perimeter plants. Say you're pulling 12.5% pool shock from a 5-gallon pail. If your downstream injector pulls at a 10:1 ratio, the mix hitting the vinyl lands right at 1.14% active SH. That's the sweet spot. It cleans siding in five minutes flat without bleaching painted trim or harming the homeowner's shrubs.
The Workbench Golden Rules: Core SH Realities
- Never Run Bleach Through the Pump: Raw bleach carries a caustic pH above 11. Feed it into your pump intake, and you'll pit brass manifolds, ruin ceramic plungers, and melt rubber packings in minutes. Always introduce chemical downstream of the unloader.
- The On-Wall Target: Vinyl siding only needs 0.8% to 1.2% active SH on the wall. A 10:1 injector pulling 12.5% pool shock delivers 1.14% automatically. Weak 20:1 factory injectors deliver only 0.60%, leaving stubborn mildew behind.
- Heat Kills Bleach: Sodium hypochlorite decomposes steadily into saltwater and oxygen. Leave a 12.5% jug in your truck bed on a 90°F (32°C) summer day, and it loses half its punch in three weeks. Buy fresh stock, keep jugs cool, and store them out of direct sunlight.
How to Mix Sodium Hypochlorite for Pressure Washing: Bleach to Water Ratio Guide
Contractors and DIYers constantly ask how to mix sodium hypochlorite for pressure washing without roasting shrubs or under-treating tough mildew. Nailing your bleach water ratio for pressure washing comes down to basic volumetric math. You match the concentration of your supply jug—usually 10% or 12.5% pool shock—to the target percentage needed for the surface.
Here is the formula for batch mixing in a tank or 5-gallon bucket:
Don't want to run algebra on the job? Use this 5-gallon batch cheat sheet. It covers both fresh 12.5% commercial SH and 10.0% retail pool shock:
| Target Surface & Substrate | Target Active SH % | 12.5% Stock Bleach (5-Gal Mix) | 10.0% Pool Shock (5-Gal Mix) | Fresh Water | Surfactant / Soap |
|---|---|---|---|---|---|
| Vinyl Siding, Gutters & Soffits | 0.8% – 1.0% | 0.40 gal (51 fl oz) | 0.50 gal (64 fl oz) | 4.50 – 4.60 gal | 2 fl oz house wash soap |
| Stucco, Dryvit & Painted Brick | 1.5% – 2.0% | 0.80 gal (102 fl oz) | 1.00 gal (128 fl oz) | 4.00 – 4.20 gal | 3 fl oz cling surfactant |
| Concrete Flatwork (Post-Treat Biocide) | 2.5% – 3.0% | 1.20 gal (154 fl oz) | 1.50 gal (192 fl oz) | 3.50 – 3.80 gal | 1 to 2 fl oz soap |
| Asphalt Shingle Roofs (Gloeocapsa magma) | 3.5% – 4.5% | 1.60 – 1.80 gal | 2.00 – 2.25 gal | 2.75 – 3.40 gal | 4 fl oz roof cling surfactant |
| Wood Decks & Fences (Cedar / Pine) | 0.5% – 0.8% | 0.25 – 0.32 gal (32–41 oz) | 0.30 – 0.40 gal (38–51 oz) | 4.60 – 4.75 gal | None (avoid foaming agents) |
Need Custom Tank Sizes or Exact Injector Draw Math?
Running a 35-gallon soft-wash skid, dialing in an X-Jet M5 proportioner, or checking your injector draw with a test bucket? Plug your specs into our free interactive tool:
Chemical Concentration Matrix: How to Mix Bleach for Siding, Roofs & Concrete
Wondering how to mix bleach for siding versus stained concrete or a blackened roof? Don't guess. Guessing will scorch surfaces or waste expensive chemical. Soft washing is all about matching active chemical strength to the substrate. Too weak, and algae survives. Too hot, and you risk oxidizing paint or yellowing wood. Use our field-tested matrix below to lock in your target on-wall SH percentage, dwell time, and injector setup:
| Substrate & Target Biofilm | Target On-Wall Active SH % | Optimal Dwell Time | Downstream Setup (12.5% Stock SH) | Downstream Setup (10.0% Pool Shock) | Dedicated 12V Batch Mix (5-Gal Ratio) | Substrate Precaution |
|---|---|---|---|---|---|---|
| Vinyl Siding & Soffits Green Algae & Mildew |
0.8% – 1.2% | 5–8 Minutes | Pull straight 12.5% through 10:1 injector (yields ~1.14%) | Pull straight 10.0% through 8:1 high-draw injector (yields ~1.11%) | 0.4 gal SH + 4.6 gal Water + 2 oz Surfactant | Don't apply at high noon. Hot siding flash-dries and leaves chalky surfactant residue. |
| Stucco, Dryvit & EIFS Porous Spore Encrustation |
1.5% – 2.0% | 10–12 Minutes | Requires 5:1 high-draw injector or dual-injector bypass | Requires 4:1 high-draw injector or dedicated 12V pump | 0.8 gal SH + 4.2 gal Water + 3 oz Surfactant | Keep rinse pressure under 100 PSI. High wand pressure punctures synthetic EIFS stucco coatings. |
| Brick & Concrete Flatwork Pre- & Post-Treat Biocide |
2.5% – 3.0% | 15 Minutes | X-Jet M5 nozzle with proportioner plug or 12V pump | X-Jet M5 without proportioner plug (yields 2.5%–3.0%) | 1.2 gal SH + 3.8 gal Water + 2 oz Surfactant | Post-treating stops spore regrowth and eliminates swirl marks for up to 12 months. |
| Asphalt Shingle Roofs Gloeocapsa magma Streaks |
3.5% – 4.5% | 15–20 Minutes | Cannot achieve via downstream; dedicated 12V pump required | Cannot achieve via downstream; dedicated 12V pump required | 1.6 to 1.8 gal SH + 3.2 to 3.4 gal Water + 4 oz Cling Surfactant | Zero high-pressure rinsing. Apply low-pressure chemical dwell only, then let rainfall rinse the shingles. |
| Cedar & Treated Softwood Surface Lichen & Gray Mold |
0.5% – 0.8% | 3–5 Minutes | Pre-dilute stock SH 50:50 in supply bucket, then downstream at 10:1 | Pre-dilute stock SH 50:50 in supply bucket, then downstream at 10:1 | 0.3 gal SH + 4.7 gal Water (No foaming soap) | Mixes over 1.0% dissolve wood lignin, furring the grain and yellowing timber. Always neutralize with oxalic acid. |
Technical Schematic: Venturi Injector Fluid Dynamics & Dilution Curve
Here is the mechanical cutaway inside a downstream chemical injector operating on Bernoulli's principle. It contrasts high-pressure bypass with low-pressure suction, alongside the physical dilution curve:
Interactive Chemical Dilution & Tank Batch Estimator
Need exact water and bleach proportions for 15, 35, 55, or 100-gallon batch tanks? Want to determine your injector siphon ratio with a bucket draw test? Calculate precise batch specs with our free interactive tool:
Pro Example: To mix 35 gallons of a 3.0% concrete pre-treat mix using 12.5% pool shock: (3.0 × 35) ÷ 12.5 = 8.4 Gallons SH, combined with 26.6 Gallons Water and 16 oz surfactant.
1. What Bleach Do Professional Pressure Washers Use? Pool Shock vs. Laundry Bleach for House Wash
I get asked this across the shop bench constantly: Can I just use regular grocery store Clorox to wash my house?
Technically yes, but practically no. Standard laundry bleach contains only 5% to 6% sodium hypochlorite. Worse, modern store jugs often contain "splash-less" additives. Those thickeners clog injector valves and foam erratically. Pull 6% grocery bleach through a 10:1 downstream injector, and you get barely 0.5% SH on the wall. That won't cut it. It is too weak to melt tough green algae and black mildew without scrubbing.
When comparing pool shock vs laundry bleach for house wash jobs, professionals always choose 12.5% commercial sodium hypochlorite or liquid pool shock. Here's why. At 12.5%, a single gallon packs more than double the punch of store bleach. It cuts dwell times down to five minutes. You can downstream straight from the jug without pre-mixing, cutting chemical costs in half.
Why Does Sodium Hypochlorite Lose Its Punch Over Time?
Bleach doesn't stay potent forever. Sodium hypochlorite (NaOCl) is chemically unstable. From the moment it's bottled, it steadily breaks down into ordinary table salt (NaCl) and either oxygen gas or inactive chlorate:
Heat is the number one enemy of SH. Every 18°F (10°C) bump in temperature roughly triples the decomposition rate:
- Stored in a cool basement at 60°F (15°C): A 12.5% jug holds strength for 5 to 6 months.
- Stored in a garage at 75°F (24°C): Usable shelf life drops to 90 to 120 days.
- Baking in a hot trailer at 95°F (35°C): Bleach degrades rapidly. Within 3 to 4 weeks, that 12.5% jug drops below 9%. Your mix will suddenly take twice as long to clear siding.
The workbench takeaway: buy fresh pool shock from high-turnover pool suppliers in vented, UV-resistant HDPE jugs. Don't stockpile bleach over the winter. Keep jugs out of direct sunlight.
2. How to Downstream Sodium Hypochlorite: Venturi Physics Made Simple
Wondering how to downstream sodium hypochlorite safely? The core tool is a compact brass fitting called a downstream chemical injector. It connects to your pump outlet, right before your high-pressure hose.
The injector runs on Bernoulli's Principle. Inside sits a conical nozzle narrowing to a 2.1mm throat. High-pressure water shoots into this restriction, accelerating rapidly. As fluid speed spikes, static pressure plunges. That drop creates a vacuum inside the throat, often pulling −20 inHg.
The vacuum lifts a ceramic check ball off its seat. It draws raw bleach up your siphon line, blending it directly into the water stream heading to your wand. Raw chemical never touches your pump. Your plungers, check valves, and manifold stay completely safe.
The Nozzle Secret: Why Backpressure Controls Chemical Flow
The biggest hurdle for beginners is grasping backpressure. Downstream injectors are backpressure-sensitive:
- Snap in a tight high-pressure tip (0°, 15°, 25°, or 40°): The tiny orifice chokes the water flow. Hose pressure spikes above 2,500 PSI. That backpressure slams the check ball shut against its seat. Suction stops instantly, letting you rinse with pure water.
- Snap in a wide low-pressure soap tip (J-Rod #30 or #40 orifice): Water dumps freely out of the wand. Line backpressure drops below 150 PSI. The venturi vacuum kicks back in, unseating the check ball. Bleach begins siphoning within seconds.
You don't need to walk back to your machine to turn valves. You switch between chemical soaping and fresh water rinsing simply by swapping your spray nozzle at the wand tip.
10:1 High-Draw vs. 20:1 Standard Injectors
Most cheap injectors included with homeowner pressure washers pull at a weak 20:1 ratio (roughly 5% chemical draw). Pull 12.5% pool shock through a 20:1 injector, and your on-wall mix drops to: 12.5 ÷ 21 = 0.59% active SH. That's too dilute for heavy green algae on shaded vinyl.
Professional contractors replace factory injectors with a high-draw 10:1 or 8:1 unit. A 10:1 injector draws approximately 10% chemical volume. Pulling raw 12.5% pool shock delivers: 12.5 ÷ 11 = 1.14% active SH at the wand tip. That's the ideal strength. It melts organic growth in a single pass while protecting paint and window trim.
3. Soft Wash Surfactants: Why Water Needs Soap to Cling
Water has high surface tension—roughly 72 dynes/cm. Spray plain water and bleach onto vertical vinyl siding or a pitched shingle roof, and it beads up instantly. It sheets off to the ground in under 60 seconds. The bleach drains away before it can kill spores.
Adding a bleach-stable surfactant breaks that surface tension down to about 30 dynes/cm. Here is why you need surfactant in your bucket:
- Vertical Cling: The surfactant creates a rich foam lather that clings to vertical siding and shingles for 10 full minutes without sliding off. The bleach stays put and does the heavy lifting.
- Deep Pore Penetration: Lower surface tension allows the solution to seep into microscopic crevices in brick, stucco, and wood grain where mold roots take hold.
- Odor Masking & Spot-Free Glass: Commercial wash soaps mask sharp chlorine fumes with cherry or citrus scents. Built-in sheeting agents prevent chalky water spots on window glass.
4. Will Pressure Washer Bleach Kill Grass and Plants? The Hydration Shield
Homeowners always ask: will pressure washer bleach kill grass, boxwoods, and garden flowers?
The straight answer: yes, if you're careless. Concentrated sodium hypochlorite strips the protective waxy coating off leaves. It pulls moisture from root systems, turning green foliage brown within 48 hours.
The good news? You don't have to smother every shrub in plastic tarps. Heavy plastic tarps in direct sunlight can cook plants faster than chemical overspray. Instead, professional soft washers protect surrounding greenery using basic plant biology: The Plant Hydration Shield.
The Engineer's 4-Step Plant Hydration Shield
- Pre-Soak All Surrounding Greenery: Before opening your chemical valve, thoroughly soak lawns, shrubs, and flower beds with fresh garden hose water. Saturated soil and bloated root cells can't absorb chlorinated runoff. Wet leaves also dilute accidental overspray on contact.
- Bag Downspouts on Roof Jobs: Washing roofs or gutters with hot 3% to 4% mixes? Wrap heavy contractor trash bags around the bottom of all gutter downspouts. Catch the concentrated chemical runoff instead of dumping it onto lawns or flower beds.
- Keep Leaves Wet While Soaping: While one tech sprays siding with the soft wash wand, keep a second hose running to mist delicate shrubbery continuously. Constant dilution is your best defense.
- Post-Wash Drench: Once the siding is clean, spend 3 to 5 minutes drenching all foliage and bed soil with clean water to wash away residual salts. For delicate Japanese maples or prized hydrangeas, mist the leaves with a mild bleach neutralizer (sodium thiosulfate).
Engineer's Bill of Materials: Precision Downstream & Soft Wash Hardware
To apply sodium hypochlorite safely without harming your pump or burning surfaces, keep these verified commercial-grade components in your rig:
| Component Name | Engineering Specification | Mechanical Purpose | Material Grade | Verified Link |
|---|---|---|---|---|
| Commercial 12.5% Sodium Hypochlorite | 12.5% Available Chlorine (NaOCl), Vented Jug | Primary oxidizing biocide; eliminates Gloeocapsa magma, lichen, and algae at the cellular root | Industrial Grade Liquid in HDPE | Check Amazon |
| High-Draw Downstream Chemical Injector | 2.1mm Orifice, 3/8" QC, 10:1 to 8:1 Draw Ratio | Siphons chemical downstream of pump unloader via Bernoulli venturi; protects pump internals | Nickel-Plated Brass, Ceramic Ball, Hastelloy Spring | Check Amazon |
| J-Rod 4-Way Soft Wash Nozzle Assembly | 1/4" QC: 0040 (Soap Stream), 2540 (Soap Fan), 0010 (Rinse Stream), 2510 (Rinse Fan) | Provides low backpressure (<150 PSI) to trigger chemical siphoning, plus 2-story reach | 304 Forged Stainless Steel | Check Amazon |
| Professional Bleach-Stable Soft Wash Surfactant | Concentrated Non-Ionic Wetting Agent (1–2 oz per 5 gal) | Lowers surface tension to 30 dynes/cm; produces cling lather, extends dwell, masks chlorine odor | Biodegradable High-Cling Formula | Check Amazon |
Field-Tested Hardware Recommendations
- Industrial 12.5% Concentration: Packs double the punch of standard 6% grocery bleach, cutting chemical costs in half.
- Optimal Downstream Dilution: Hits a true 1.14% active chlorine mix through a 10:1 injector—ideal for single-pass siding washes.
- UV-Resistant Vented Packaging: Shipped in heavy-duty HDPE containers with breathable caps to prevent pressure buildup during storage.
- High-Draw 10:1 Ratio: Outperforms weak 20:1 factory injectors by pulling roughly 10% chemical volume. You wash houses fast without pre-mixing batch tanks.
- Chemical-Resistant Internals: Fitted with a precision ceramic check ball and Hastelloy spring that resist chlorine pit corrosion far longer than stainless steel.
- Standard 3/8" Quick Connects: Plugs directly between your unloader discharge port and high-pressure hose line with zero pipe threading.
- Instant Backpressure Drop: High-orifice soap tips (0040 stream and 2540 fan) drop line backpressure below 150 PSI to pull chemical immediately.
- Two-Story Chemical Reach: Shoots a tight soap stream up to 30 feet high. Clean two-story vinyl siding with both feet on the turf.
- Integrated Stainless Rinse Tips: Switch between chemical soaping and low-pressure rinsing (0010 and 2510) in seconds with a quick flip of the holder.
- Bleach-Stable Formulation: Won't curdle, separate, or break down the active hypochlorite in concentrated stock buckets.
- Maximum Vertical Cling: Produces a rich shaving-cream foam that keeps active bleach pinned to vertical siding for full dwell time.
- Masking & Rinsing Agents: Features fresh scent additives to mask chlorine odors, plus wetting agents that promote spot-free window drying.
Step-by-Step Checklist: How to Downstream SH Safely
Follow this field-tested sequence to wash residential siding quickly without damaging equipment or delicate property plantings:
- Hook Up Your Rig: Connect your garden hose to the pump inlet. Click your downstream injector into the pump outlet, and attach your 50- or 100-foot hose to the injector. Set your 12.5% pool shock jug beside the machine and drop in the siphon line with its weighted filter.
- Pre-Soak the Perimeter: Check that all house windows are shut tight and tape over outdoor electrical outlets. Grab your garden hose and drench all shrubs, grass, and flower beds around the work area.
- Purge Air and Start the Engine: Squeeze the spray gun trigger to bleed air from the pump and hose for 30 to 45 seconds. Once water flows steadily, start the pressure washer engine.
- Engage Chemical Draw: Click your low-pressure soap tip (0040 or 2540) into the wand. Within 15 to 20 seconds, line backpressure drops. The stream turns pale yellow with a light foam as the injector pulls bleach.
- Apply Bottom to Top: Spray the siding horizontally, working from the bottom foundation upward toward the gutters. Applying bottom-to-top ensures the chemical coats dry algae evenly without streaks running down dry walls.
- Let It Dwell for 5 to 8 Minutes: Watch the chemistry work. Green algae turns brown, shifts to dull yellow, and vanishes. Never let bleach dry completely on siding or glass. If the sun is beating down on the wall, mist it lightly with fresh water to keep it damp.
- Rinse Top to Bottom: Snap a wide low-pressure rinse tip (such as the J-Rod 2510) into the wand, or switch to your high-pressure nozzle to shut off chemical draw. Pull the siphon tube out of the bleach bucket and drop it into clean water. Rinse the house thoroughly from the gutters down.
- Final Plant Flush: Spend 3 to 5 minutes drenching all surrounding shrubs, foundation soil, and window frames with fresh garden hose water.
System Decontamination: Post-Wash Rig Flush Protocol
Leaving sodium hypochlorite inside a downstream injector will ruin it. As water evaporates, razor-sharp sodium chloride (salt) crystals precipitate out. Those crystals freeze the check ball to its seat and pit the spring. Protect your rig with this 2-minute shutdown protocol:
- Flush the Siphon Tube with Fresh Water: Pull the weighted chemical strainer out of your SH jug and drop it into a bucket of clean fresh water. With a low-pressure soap tip installed, pull the trigger for 60 to 90 seconds. That flushes raw bleach out of the siphon tube, injector chamber, and high-pressure hose.
- Neutralize with Silicone Spray: After flushing, disconnect the chemical tubing. Spray a short burst of silicone lubricant or WD-40 into the injector's brass hose barb to keep the check ball floating freely on its spring.
- Depressurize the System: Shut off the engine, turn off the water spigot, and squeeze the spray gun trigger into the grass to vent trapped hydrostatic pressure. Never store pressure hoses under static pressure.
