Pressure Washing Chemicals
Table of Contents
What you will learn
💡 Frequently Asked Questions
Find quick answers to common questions about pressure washing chemicals.
Why Chemistry Matters More Than PSI
When most people think about pressure washing, they focus on the hardware: pump GPM, nozzle spray angle, and PSI rating. But veteran contractors know a different truth—the chemical does 80% of the work, and the water does the remaining 20%. The right chemistry breaks molecular bonds, lifts embedded contaminants, kills biological growth at the root, and protects the surface for months afterward.
Using water pressure alone to blast away oil stains, algae, or mineral deposits often damages the substrate before the stain is fully removed. Chemical pre-treatment (known as "downstreaming" or "soft washing") loosens contaminants so lower pressure can rinse them away cleanly. This approach preserves concrete aggregate, prevents wood fiber damage, and extends the life of painted and vinyl surfaces.
In this guide, we cover every major chemical class used in professional pressure washing, the correct surfaces and dilution ratios for each, and the safety protocols that protect both the operator and the environment. Whether you run a commercial fleet-wash operation or you are a homeowner tackling your annual driveway cleaning, this resource will help you select and apply the right products.
The Six Chemical Classes for Pressure Washing
Professional pressure washing chemicals fall into six broad categories. Each targets a different family of contaminants, and understanding their strengths helps you avoid wasted product, surface damage, and safety incidents.
1. Alkaline Cleaners (Sodium Hydroxide / Caustic Soda)
Alkaline cleaners are the workhorses of commercial pressure washing. Sodium hydroxide (NaOH) solutions in the 25–50% range saponify fats, dissolve proteins, and cut through heavy grease layers that acids cannot touch. They are the go-to choice for restaurant hoods, loading docks, and fleet-wash bays. Caustic soda at lower dilutions (1–3%) also excels at stripping oxidized paint from wood decks before refinishing.
- Best for: Grease, oil, animal fats, carbon buildup, oxidized paint
- Typical dilution: 1:5 to 1:15 depending on task
- Products: Sodium Hydroxide 25% and 50% Solutions
2. Oxidizing Agents (Sodium Hypochlorite / Bleach)
Sodium hypochlorite (NaOCl) at 12.5% concentration is the gold standard for soft washing roofs, vinyl siding, and concrete affected by algae, mold, mildew, or lichen. The hypochlorite ion penetrates organic growth and destroys it at the cellular level, which means the stain does not return for 12–18 months—far longer than pressure-only cleaning. For pressure washers, 12.5% sodium hypochlorite is diluted downstream to a final strength of roughly 0.5–1.5% on the surface.
→ Deep Dive: Using Sodium Hypochlorite—Concentration, Dilution, and Safety- Best for: Algae, mold, mildew, lichen, organic stains
- Typical dilution: 1:4 to 1:10 (downstream) yielding 0.5–1.5% on surface
- Products: Sodium Hypochlorite 12.5% and 5.25%
3. Acid Cleaners (Hydrochloric / Muriatic Acid)
Acid-based cleaners dissolve mineral deposits, rust, efflorescence (the white powder that forms on masonry), and hard-water scale. Hydrochloric acid (HCl, also called muriatic acid) is the most common choice for concrete and brick. Phosphoric acid is a milder alternative for sensitive surfaces. Oxalic acid handles rust stains on wood decks without bleaching the wood fibers.
→ Related: The Complete Guide to Cleaning Stone and Concrete with Muriatic Acid- Best for: Efflorescence, rust, mineral scale, hard-water stains, concrete etching
- Typical dilution: 1:5 to 1:20 depending on acid strength
- Products: Hydrochloric Acid, Full Acids Collection
4. Surfactant-Based Detergents (TSP and Blends)
Trisodium phosphate (TSP) and surfactant-based detergent blends are versatile, moderate-strength cleaners for general-purpose work. TSP boosts the cleaning power of both alkaline and oxidizing washes, improves chemical "cling" on vertical surfaces, and is a proven pre-paint surface prep agent. Many professional house-wash mixes combine TSP with sodium hypochlorite for a one-pass clean-and-sanitize approach.
→ Learn More: The Ultimate Guide to TSP Cleaner for Powerful Cleaning- Best for: General dirt, grime, chalky paint, pre-paint prep
- Typical dilution: 1/2 cup per gallon (general), 1 cup per gallon (heavy duty)
- Products: Salts and Inorganic Compounds
5. Solvent-Based Degreasers (D-Limonene, Acetone, Toluene)
Solvent-based products dissolve petroleum-based contaminants that water-based chemicals cannot break down. D-Limonene (citrus solvent) is the eco-friendly option—derived from orange peels, it handles light-to-moderate grease, adhesive residue, and tar spots. For heavier industrial work, acetone and toluene cut through paint overspray, epoxy residue, and hardened coatings. These solvents are typically applied by hand or low-pressure sprayer before the pressure rinse.
→ Eco-Friendly Option: D-Limonene—The Citrus-Based Cleaning Powerhouse- Best for: Tar, adhesive, grease, paint overspray, petroleum stains
- Application: Direct spray or wipe, then low-pressure rinse
- Products: D-Limonene, Acetone, Full Solvents Collection
6. Organic Acids (Citric, Vinegar/Acetic, Oxalic)
When you need acidic cleaning power without the intensity of muriatic acid, organic acids offer a safer, more eco-friendly path. Citric acid removes hard-water scale from glass and stainless steel. White vinegar (acetic acid at 10–30% concentration) dissolves light mineral deposits and neutralizes alkaline residues left by previous cleaning passes. Oxalic acid is unmatched for removing tannin stains and rust from wood decks.
→ Versatile Cleaner: The Many Uses of 10% and 30% Vinegar in Cleaning- Best for: Hard-water spots, tannin stains, rust on wood, light mineral deposits
- Typical dilution: Varies; citric acid 2–5% solution, vinegar often used full-strength
- Products: Organic Acids, Acetic Acid Glacial
Chemical Selection by Surface Type
Choosing the wrong chemical for a surface can cause etching, discoloration, or structural damage. The table below maps each surface type to its recommended chemical classes and critical cautions.
| Surface | Recommended Chemicals | Avoid | Max PSI |
|---|---|---|---|
| Concrete (driveways, sidewalks) | Sodium hydroxide (degreaser), sodium hypochlorite (bio stains), muriatic acid (efflorescence) | Citrus solvents on fresh concrete (<30 days) | 3000-4000 |
| Brick & Masonry | Muriatic acid (1:10), oxalic acid (rust), sodium hypochlorite (algae) | Strong alkalis on lime-mortar joints | 1500-2500 |
| Wood Decks & Fences | Sodium percarbonate (oxygen bleach), oxalic acid (brightener), mild detergent | Sodium hypochlorite >1% (damages fibers), muriatic acid | 500-1200 |
| Vinyl Siding | Sodium hypochlorite 0.5-1% (soft wash), TSP surfactant blend | Acetone, toluene (melts vinyl), high PSI | 1000-1500 |
| Painted Surfaces | Mild detergent, TSP (prep), sodium hypochlorite <0.5% | Strong acids, strong alkalis, solvents | 800-1200 |
| Metal / Steel | Phosphoric acid (rust converter), alkaline degreaser, citric acid | Muriatic acid (causes flash rust), sodium hypochlorite on bare steel | 2000-3000 |
| Stucco / EIFS | Sodium hypochlorite soft wash (<1%), gentle surfactant | All acids, high PSI, scrubbing | 500-800 |
| Asphalt / Roofing | Sodium hypochlorite soft wash, surfactant for cling | Pressure over 100 PSI, petroleum solvents | 60-100 (soft wash only) |
Professional Dilution Ratios Reference
Proper dilution ensures maximum cleaning power without surface damage or chemical waste. These ratios assume a downstream chemical injector with a typical 10:1 draw ratio. Adjust for your specific equipment.
| Chemical | Stock Concentration | In-Bucket Ratio | On-Surface Strength | Primary Use |
|---|---|---|---|---|
| Sodium Hypochlorite | 12.5% | 1:3 (bucket) | ~1% on surface | House wash, vinyl, stucco |
| Sodium Hypochlorite | 12.5% | 1:1 (bucket) | ~1.5% on surface | Roof wash, heavy mold |
| Sodium Hydroxide | 25% | 1:5 to 1:10 | 2.5–5% | Degreasing concrete, hoods |
| Sodium Hydroxide | 50% | 1:15 to 1:20 | 2.5–3.3% | Fleet wash, heavy grease |
| Muriatic Acid (HCl) | 31.45% | 1:10 to 1:20 | 1.5–3% | Efflorescence, rust, etching |
| Citric Acid | Powder (dissolve) | 2–5 oz per gallon | 2–5% | Hard-water spots, brightening |
| Oxalic Acid | Powder (dissolve) | 4–6 oz per gallon | 3–5% | Wood brightening, rust removal |
| TSP | Powder (dissolve) | 1/2–1 cup per gallon | N/A (surfactant boost) | General cleaning, paint prep |
Pressure Settings by Application
Matching your PSI and nozzle selection to the job prevents damage and maximizes chemical contact time. Lower pressure with the right chemistry almost always outperforms high pressure without chemistry.
| Application | Recommended PSI | Nozzle Tip | Chemical Method | Dwell Time |
|---|---|---|---|---|
| Roof Soft Wash | 60–100 | Black (65°) or dedicated soft-wash nozzle | 12V pump or batch sprayer | 15–20 min |
| House / Vinyl Siding | 800–1200 | White (40°) | Downstream injector | 10–15 min |
| Concrete Flatwork | 2500–4000 | Surface cleaner attachment | Pre-treat + downstream | 10–15 min |
| Wood Deck | 500–1200 | White (40°) or Green (25°) from distance | Pump sprayer pre-soak | 10–20 min |
| Fleet / Vehicle Wash | 1200–2000 | White (40°) | Foam cannon or downstream | 5–10 min |
| Graffiti Removal | 2000–3000 | Yellow (15°) or Turbo nozzle | Direct chemical application | 15–30 min |
| Brick / Masonry | 1500–2500 | Green (25°) | Pre-wet + pump sprayer | 5–10 min |
| Heavy Equipment | 2500–3500 | Green (25°) or Yellow (15°) | Foam cannon | 10–15 min |
Application Guide: Matching Chemicals to the Job
Different jobs require different chemical strategies. Below are step-by-step approaches for the most common pressure washing applications.
Residential House Wash
The bread-and-butter of professional pressure washing. A soft-wash approach with sodium hypochlorite and TSP surfactant handles 90% of residential exteriors.
- Pre-wet plants and landscaping
- Mix 12.5% SH at 1:3 with TSP surfactant
- Downstream apply bottom-to-top
- Dwell 10–15 min, rinse top-to-bottom
- Neutralize plants with water rinse
Commercial Building Wash
Larger scale, tougher stains, and often stricter environmental regulations. Reclaim wastewater when required by local ordinance.
- Assess surface type (EIFS, brick, metal panel)
- Select appropriate chemical for substrate
- Section building into manageable zones
- Apply and rinse zone by zone to prevent dry lines
- Document before/after for client
Fleet & Vehicle Washing
Truck fleets, trailers, and heavy equipment accumulate road grime, diesel soot, and bug splatter. Alkaline two-step processes are the industry standard.
- Step 1: Apply alkaline presoak (NaOH 1:10)
- Step 2: Rinse and apply acidic brightener
- Use foam cannon for maximum dwell
- Rinse thoroughly with high volume
- Reclaim water for compliance
Graffiti Removal
Graffiti removal requires solvent-based chemistry. Acetone, MEK, or proprietary graffiti removers dissolve spray paint and marker ink from masonry, metal, and coated surfaces.
- Test chemical on inconspicuous area first
- Apply solvent, allow 15–30 min dwell
- Agitate with stiff brush if needed
- Pressure rinse at 2000–3000 PSI
- Apply anti-graffiti coating after
Concrete Restoration
Oil stains, tire marks, rust, and efflorescence require a multi-chemical approach. Degrease first, then treat specific stains, then brighten.
- Apply NaOH degreaser to oil stains
- Treat efflorescence with muriatic acid 1:10
- Remove rust with oxalic or phosphoric acid
- Surface-clean at 3000+ PSI
- Post-treat with citric acid to brighten
Eco-Friendly & Sensitive Areas
Near waterways, gardens, or where children and pets are present, choose biodegradable chemistry. D-Limonene, citric acid, and sodium percarbonate offer effective cleaning with minimal environmental impact.
- Use D-Limonene for grease and adhesive
- Sodium percarbonate for organic stains
- Citric acid for mineral deposits
- Capture and filter all runoff
- Follow local environmental regulations
Safety Protocols for Pressure Washing Chemicals
Chemical handling is the single biggest safety concern in the pressure washing industry. More injuries occur from chemical contact and inhalation than from pressure-related incidents. Follow these protocols on every job.
⚠️ Required Personal Protective Equipment (PPE)
- Chemical-resistant gloves – Nitrile minimum; PVC or butyl rubber for strong acids/bases
- Safety goggles or face shield – Splash-proof, not just impact-rated
- Rubber boots – Chemical-resistant footwear for ground-level application
- Respirator – Half-face with organic vapor/acid gas cartridges for enclosed areas
- Long sleeves and pants – Chemical-resistant apron for mixing operations
The Cardinal Rules of Chemical Mixing
- Never mix acids with bleach (sodium hypochlorite). This reaction produces chlorine gas, which is toxic and potentially fatal even in small concentrations. If switching from an acid wash to a bleach wash, thoroughly rinse all equipment and surfaces between applications.
- Always add chemical to water, never water to chemical. Adding water to concentrated acid or caustic can cause violent exothermic reactions, splashing, and boiling.
- Label every container. Pressure wash chemicals in unmarked buckets are responsible for numerous accidental exposures each year.
- Keep SDS sheets on-site. Every chemical you use must have a Safety Data Sheet accessible at the job site. This is not optional—it is an OSHA requirement.
- Neutralize before disposal. Acid and alkaline wash water should be pH-tested and neutralized before entering storm drains (where permitted) or collected for proper disposal.
Environmental Compliance
The Clean Water Act and local regulations govern what can enter storm drains and waterways. In most jurisdictions, no pressure wash wastewater may enter a storm drain without treatment, regardless of the chemicals used. Best practices include:
- Use berms and containment mats to capture runoff
- Filter wastewater through sediment bags before disposal
- Test pH of wastewater (must typically be 6.0–9.0 for discharge)
- Document disposal methods for each job
- Consider reclaim systems for high-volume commercial work
Frequently Asked Questions
Can I use household bleach (sodium hypochlorite 5.25%) instead of professional 12.5%?
Technically yes, but it is far less cost-effective and requires much higher proportions in your mix to achieve the same on-surface concentration. Professional 12.5% sodium hypochlorite delivers roughly 2.4 times the active chlorine per gallon. Household bleach also often contains fragrances and thickeners that can clog downstream injectors. For any job beyond a small patio, 12.5% is the professional standard.
What is the "two-step" process in fleet washing?
The two-step method uses an alkaline presoak (sodium hydroxide solution) followed by an acidic rinse (typically hydrofluoric acid blend or phosphoric acid). Step one breaks down organic soils and grease. Step two dissolves mineral deposits and road film while brightening aluminum and stainless steel. This approach delivers a showroom finish on commercial vehicles and is the industry standard for fleet wash operations.
How do I prevent chemical damage to landscaping?
Pre-wet all plants, grass, and soil thoroughly before applying chemicals. Sodium hypochlorite is the biggest landscaping risk—it kills vegetation on contact at working concentrations. After the wash, rinse all nearby vegetation again. For added protection, apply a plant-safe neutralizing agent (like a dilute sodium thiosulfate solution) to plantings adjacent to the work area. Some contractors also cover sensitive plants with plastic sheeting during application.
What chemical removes oil stains from concrete driveways?
Fresh oil stains respond well to sodium hydroxide (caustic soda) at 1:5 dilution, applied and allowed to dwell for 15–20 minutes before pressure rinsing at 3000+ PSI with a surface cleaner. Old, deeply penetrated oil stains may require a poultice treatment: apply a sodium hydroxide solution, cover with an absorbent material (cat litter or diatomaceous earth), let it draw out the oil for 24 hours, then sweep and pressure wash. Multiple treatments may be necessary for stains that have set for years.
Is it safe to use muriatic acid on colored or stamped concrete?
Proceed with extreme caution. Muriatic (hydrochloric) acid can etch the surface finish and lighten integral color in stamped and colored concrete. Always test a small, inconspicuous area first. For colored concrete, phosphoric acid or citric acid at a weaker dilution is usually the safer choice. If muriatic acid is necessary, use a very dilute solution (1:20 or weaker), keep dwell time under 5 minutes, and neutralize immediately with a baking soda rinse.
Source Your Pressure Washing Chemicals from Alliance Chemical
Professional-grade sodium hypochlorite, sodium hydroxide, muriatic acid, D-Limonene, citric acid, and more—available in sizes from quarts to 55-gallon drums. Fast shipping nationwide.
Shop Cleaning ChemicalsFrequently Asked Questions
What chemicals are used in pressure washing?
Common pressure washing chemicals include sodium hydroxide (heavy degreasing, house washing), sodium hypochlorite (mold, mildew, and algae killing), surfactants (improving chemical adhesion to surfaces), oxalic acid (rust and tannin stain removal), phosphoric acid (concrete etching), and citric acid (light descaling). Choose chemicals based on the surface and type of stain.
What is the best chemical for pressure washing a house exterior?
For vinyl, aluminum, or painted siding: sodium hypochlorite (bleach) at 1-3% with surfactant kills mold, mildew, and algae (soft wash technique). For heavy organic soils: sodium hydroxide-based housewash detergent. Apply chemicals at low pressure (soft wash), dwell 5-10 minutes, then rinse at 1,000-1,500 PSI. Never use high pressure on siding—it causes damage.
How do you remove oil stains from concrete with pressure washing?
Pre-treat oil stains with sodium hydroxide-based degreaser (10-15% concentration), let dwell 10-15 minutes, agitate with stiff brush, then pressure wash at 2,500-3,500 PSI with a 15° nozzle. For old, set-in stains, apply degreaser overnight before washing. Heated pressure washing (200°F) dramatically improves oil removal on concrete.
What safety precautions are needed when using chemicals with pressure washers?
Wear chemical-resistant gloves, safety glasses, and rubber boots. Never mix bleach with other chemicals (especially ammonia or acids). Protect landscaping by pre-wetting plants and rinsing after chemical application. Use downstream injection for chemical application (low pressure) and clear water for high-pressure rinsing. Contain runoff per local regulations.
