Pressure Washing Guide

PSI selection by surface, nozzle tips, detergent usage, and technique for common surfaces

Understanding Pressure Washing Basics

Pressure washing (also called power washing) uses high-pressure water spray to remove dirt, grime, mold, loose paint, and other contaminants from surfaces. The combination of PSI (pounds per square inch—force of water), GPM (gallons per minute—volume of water), and proper technique determines cleaning effectiveness and safety.

Power washing technically refers to using heated water, while pressure washing uses unheated water. For most residential applications, cold-water pressure washers are sufficient and more affordable.

Key Principle: More pressure is not always better. Using too much pressure or the wrong nozzle can damage surfaces, strip paint, etch concrete, splinter wood, break windows, and cause serious injury. Matching PSI, nozzle, and technique to the surface is critical for safe, effective cleaning.

PSI Recommendations by Surface Type

Surface	PSI Range	Recommended Nozzle	Notes
Windows & Screens	500-1,000 PSI	40° (white) or soap nozzle	Use very low pressure. Stay 2-3 ft away. Never use narrow nozzles—can break glass instantly.
Vinyl Siding	1,300-1,600 PSI	25° (green) or 40° (white)	Spray from bottom up, rinse top down. Never spray up under siding edge. Avoid pressure on seams.
Aluminum Siding	1,200-1,500 PSI	25° (green)	Lower pressure than vinyl. Can dent easily. Use wider angle nozzle and keep 3+ ft distance.
Wood Siding & Fencing	500-1,200 PSI	25° (green) or 40° (white)	Very low pressure to avoid splintering. Follow wood grain. Test inconspicuous area first.
Wood Decks	500-1,500 PSI	25° (green) or 40° (white)	Use lowest effective pressure. Follow grain direction. 8-12" distance. Higher PSI strips wood fibers.
Composite Decking	1,500-2,000 PSI	25° (green) or 40° (white)	More durable than wood but still avoid narrow nozzles. Follow manufacturer recommendations.
Brick & Masonry	1,500-2,500 PSI	15° (yellow) or 25° (green)	Hard surfaces tolerate more pressure. Avoid deteriorated mortar. Can use rotating nozzle for heavy stains.
Stucco	1,200-1,600 PSI	25° (green) or 40° (white)	Moderate pressure. Cracked or damaged stucco can be blown off by high pressure. Test first.
Concrete Driveways	2,500-3,000 PSI	15° (yellow) or 25° (green)	Can handle high pressure. Rotating turbo nozzle excellent for oil stains and heavy grime.
Asphalt Driveways	1,500-2,000 PSI	25° (green)	Lower than concrete. Old/deteriorated asphalt can be damaged by high pressure. Keep moving.
Roof Shingles	1,000-1,500 PSI	40° (white) ONLY	Low pressure critical—can dislodge granules and shorten roof life. Spray downward only. Consider soft washing instead.
Cars & Vehicles	1,200-1,900 PSI	40° (white) or soap nozzle	Detergent first, rinse top to bottom. Keep 12-18" away. Never use narrow nozzles—strips paint and damages trim.
Patio Furniture (plastic)	1,000-1,500 PSI	25° (green) or 40° (white)	Moderate pressure safe for most resin furniture. Test first on underside.

Choosing the Right Pressure Washer

Light-duty (1,000-1,900 PSI): Electric, budget-friendly, good for cars, patio furniture, light house washing
Medium-duty (2,000-2,800 PSI): Electric or gas, most versatile for homeowners—decks, siding, driveways
Heavy-duty (2,900-3,200+ PSI): Gas-powered, professional-grade, concrete, heavy stains, commercial use
GPM matters too: Higher GPM (gallons per minute) = faster cleaning. 2.0-2.5 GPM typical for residential.
Cleaning units: PSI × GPM = cleaning power. 2,500 PSI @ 2.5 GPM = 6,250 cleaning units.

Nozzle Tip Color Coding and Spray Angles

Pressure washer nozzles are color-coded by spray angle. Narrower angles = higher pressure at impact point. Always start with the widest angle (lowest pressure) and work down if needed.

Color	Angle	Pressure Impact	Best Uses	Dangers
🔴 Red (0°)	0° (Pinpoint)	MAXIMUM (100%)	Extremely stubborn stains, concrete, rust removal, crevices. Professional use mainly.	⚠️ EXTREME DANGER. Can cut skin, break glass, damage nearly any surface. Causes most injuries. Use with extreme caution.
🟡 Yellow (15°)	15° (Narrow)	Very High (75-90%)	Heavy-duty concrete cleaning, paint stripping, masonry, deep stains.	Can etch concrete, strip paint aggressively, splinter wood. Keep moving. Not for soft surfaces.
🟢 Green (25°)	25° (Medium)	High (50-60%)	General purpose—driveways, decks, siding, fences. Most common nozzle for everyday cleaning.	Can still damage soft wood, delicate surfaces. Test first on inconspicuous area.
⚪ White (40°)	40° (Wide)	Medium (30-40%)	Windows, vehicles, vinyl siding, boats, delicate surfaces. Safest for most applications.	Lower risk but can still break windows if too close. Maintain proper distance (2-3 ft).
⚫ Black (Soap)	65° (Widest)	Very Low (10-15%)	Applying detergent/soap. Low pressure allows detergent to dwell without running off.	None—safe for all surfaces. Detergent only—does not clean by itself. Must switch to pressure nozzle to rinse.
🔵 Rotating Turbo	0° rotating in 4-8" circle	Very High (concentrated)	Concrete, heavy stains, oil spots, graffiti. Combines 0° power with 15° coverage.	Can etch concrete in one spot. Keep moving at steady pace. Never use on wood, siding, or soft materials.

Critical Safety Rule: Never use red (0°) or yellow (15°) nozzles on windows, siding, wood, vehicles, or any soft material. These narrow angles can cause instant, irreversible damage and serious injuries. Always test on inconspicuous area first when using a new nozzle or surface.

Nozzle Selection Rule of Thumb

• Start wide, go narrow if needed: Begin with 40° (white) or 25° (green), only increase pressure if surface isn't getting clean
• Match to hardness: Softer surfaces = wider angles (lower pressure impact)
• Distance compensates: Can use narrower nozzle if you stay farther away (pressure decreases with distance)
• Keep moving: Never hold any nozzle in one spot—causes streaks, etching, or damage
• Turbo nozzle caution: Extremely effective but can damage almost anything if misused. Only for concrete and masonry.

Detergent Types, Dilution, and Proper Usage

Pressure washer detergents (also called soaps) are specially formulated to work with pressure washers. Regular household cleaners create excessive suds and can damage the pump. Detergents break down dirt, grease, mold, and mildew, allowing water pressure to rinse them away more effectively.

Detergent Type	Best For	Dilution Ratio	Notes
All-Purpose Cleaner	General cleaning—siding, decks, driveways, fences	1:10 to 1:20 (concentrate:water)	Most versatile. Good starting point for most jobs. Biodegradable formulas available.
House Wash / Siding Cleaner	Vinyl, aluminum, painted siding	Ready-to-use or 1:4 dilution	Often contains mildewcide. Safe for most painted surfaces. Rinse thoroughly.
Concrete & Driveway Cleaner	Concrete, brick, stone, asphalt	1:3 to 1:10 depending on soil	Higher alkalinity for oil/grease. Can contain degreasers. Protect plants—can damage landscaping.
Wood Deck Cleaner	Wood decks, fences, outdoor wood furniture	Ready-to-use or 1:4 dilution	Mild formula to avoid damaging wood fibers. Often contains brightener. Follow with deck brightener for best results.
Vehicle Wash Soap	Cars, trucks, boats, RVs	1:20 to 1:50 (very dilute)	pH-neutral, won't strip wax or damage paint. Extra-gentle formulation. Specific automotive pressure washer soap recommended.
Mold & Mildew Remover	Heavy mold/mildew on any surface	Ready-to-use or 1:3 dilution	Contains bleach or sodium hypochlorite. Very effective but protect plants and landscaping. Rinse thoroughly.
Degreaser	Engine blocks, garage floors, oil stains	1:4 to 1:10	Heavy-duty alkaline cleaner. Excellent for petroleum-based stains. Can damage plants—contain runoff.

Detergent Application Process

Step 1: Pre-Rinse (Optional but Recommended)

• Use pressure nozzle (25° or 40°) to remove loose dirt and wet surface
• Makes detergent more effective by allowing better surface contact
• Skip this step for delicate surfaces like wood

Step 2: Apply Detergent

• Switch to black soap nozzle (low pressure) or use downstream injector
• Fill pressure washer detergent tank with properly diluted soap
• Apply detergent from bottom to top (prevents streaking)
• Work in sections small enough to keep wet before dwell time expires
• Apply generously but avoid excessive runoff

Step 3: Dwell Time (Critical)

• Allow detergent to sit and work (typically 5-10 minutes)
• Don't let detergent dry on surface—rewet if needed
• Check product instructions—some require longer dwell for heavy soil
• On hot days, work in shade or smaller sections to prevent drying

Step 4: Agitate if Needed

• For heavy soil, use soft brush to agitate while detergent is on surface
• Especially effective for vertical surfaces (siding, fences)
• Don't scrub wood decks hard—can damage softened fibers

Step 5: Rinse from Top to Bottom

• Switch to pressure nozzle (25° or 40° for most surfaces)
• Rinse from top to bottom (gravity helps remove soap)
• Rinse thoroughly—soap residue attracts dirt and looks streaky
• Overlap rinse strokes for even cleaning
• Protect plants—rinse nearby vegetation with garden hose after

Detergent Safety and Environmental Considerations

Protect landscaping: Many detergents (especially concrete cleaners and degreasers) can harm plants. Pre-wet plants, cover delicate vegetation, rinse thoroughly after
Prevent runoff: Soaps and chemicals entering storm drains flow directly to waterways. Use biodegradable products when possible. Contain runoff if using harsh chemicals
Never use dish soap: Creates excessive foam, doesn't rinse cleanly, can damage pressure washer pump
Wear PPE: Splashback is common. Wear safety glasses, closed-toe shoes, long pants. Chemical-resistant gloves for harsh detergents
Read labels: Mixing incompatible chemicals (bleach + ammonia) creates toxic fumes. Follow manufacturer instructions

Proper Technique, Distance, and Common Mistakes

Distance Guidelines by Surface

• 6-12 inches: Concrete, asphalt (with appropriate nozzle)
• 8-12 inches: Wood decks (following grain), composite decking
• 12-18 inches: Brick, stone, masonry
• 12-24 inches: Siding (vinyl, aluminum), painted surfaces
• 18-24 inches: Vehicles, windows (with 40° nozzle only)
• 24-36 inches: Screens, soft wood, delicate surfaces
• Rule: Start farther away and move closer until surface cleans effectively. Never start close.

Proper Technique

• Angle the spray: 45° angle works best for most surfaces. Perpendicular (90°) can drive water under siding or into cracks.
• Overlap strokes: Overlap each pass by 6-8" for even cleaning and no streaks
• Consistent speed: Move at steady pace—too slow etches concrete, too fast misses dirt
• Smooth, sweeping motion: Long horizontal or vertical strokes. Avoid jerky movements.
• For decks: Always follow wood grain direction. Cross-grain cleaning causes furry texture.
• For siding: Work in sections from bottom to top (soap application), top to bottom (rinsing)
• For driveways: Work in sections, push water toward drainage. Use turbo nozzle on heavy stains.

Common Pressure Washing Mistakes

❌ Too much pressure: Causes etching, splintering, paint removal, damage. More pressure ≠ better cleaning.
❌ Wrong nozzle: Using narrow nozzle (red or yellow) on soft surfaces causes instant damage
❌ Holding in one spot: Creates uneven cleaning, tiger stripes, etching, or holes in wood
❌ Spraying upward under siding: Drives water behind siding, causes mold and rot inside walls
❌ Not testing first: Always test on inconspicuous area before doing entire surface
❌ Skipping detergent: Trying to blast dirt off with pressure alone—detergent does the work, pressure just rinses
❌ Wrong detergent: Using dish soap (foams excessively) or harsh chemicals on wrong surface
❌ Insufficient rinse: Soap residue attracts dirt and looks hazy. Rinse until water runs clear.
❌ Too close to electrical: Water and electricity = danger. Stay away from outlets, fixtures, service panels
❌ Ignoring ladder safety: Pressure washer kickback on ladder = fall risk. Use extension wand instead.

Testing Pressure and Technique

Before cleaning any new surface:

Choose widest nozzle appropriate for surface (usually 40° or 25°)
Test on hidden area (side of house, under deck, corner of driveway)
Start 3 feet away and gradually move closer while cleaning
Observe results—if not cleaning, move closer or switch to narrower nozzle
If seeing damage (streaks, etching, splintering), back away or use wider nozzle
Once you find effective distance and nozzle, maintain that throughout job

Surface-Specific Pressure Washing Guides

Wood Decks

• Pressure: 500-1,200 PSI max. Use lowest effective pressure.
• Nozzle: 25° or 40°. Never use red, yellow, or turbo nozzle.
• Distance: 8-12 inches from surface
• Technique: Follow grain direction always. Consistent speed. Overlap strokes.
• Detergent: Wood deck cleaner. Let dwell 10-15 minutes. Agitate with brush if needed.
• After cleaning: Apply deck brightener (oxalic acid) to restore color and neutralize cleaner
• Timing: Allow 48 hours dry time before staining or sealing
• Warning: High pressure "fuzzies" wood by raising fibers. Requires sanding to smooth.

Vinyl Siding

• Pressure: 1,300-1,600 PSI
• Nozzle: 25° or 40°
• Distance: 12-18 inches
• Technique: Spray from bottom to top when applying detergent (prevents streaks). Rinse from top to bottom.
• Angle: Never spray upward under siding edges—drives water behind siding
• Detergent: House wash or mild all-purpose cleaner. Mildewcide if needed.
• Caution: Cracked or loose siding can be ripped off by high pressure. Inspect first.

Concrete Driveways

• Pressure: 2,500-3,000 PSI (concrete can handle it)
• Nozzle: 15° or 25°. Turbo nozzle excellent for oil stains.
• Distance: 6-12 inches
• Technique: Work in sections. Push water toward drainage. Consistent speed to avoid stripes.
• Detergent: Concrete cleaner or degreaser. Let dwell 10-15 minutes on oil stains.
• Oil stains: Pre-treat with degreaser, agitate with brush, pressure wash with turbo nozzle
• Sealing: Consider sealing concrete after cleaning for easier maintenance

Vehicles

• Pressure: 1,200-1,900 PSI. Lower is safer.
• Nozzle: 40° (white) ONLY. Never use narrow nozzles.
• Distance: 12-18 inches minimum
• Technique: Rinse top to bottom. Soap with black nozzle. Let dwell 5 min. Rinse top to bottom.
• Detergent: Automotive pressure washer soap only (pH-neutral, won't strip wax)
• Avoid: Don't pressure wash engine bay without covering sensitive electronics. Don't spray direct at body seams, trim, or emblems (can strip off).
• After: Dry with microfiber to prevent water spots

Roofs (Shingles)

• Caution: Pressure washing roofs is controversial—can shorten shingle life by removing granules
• Alternative: "Soft washing" (low-pressure chemical cleaning) is safer and often more effective
• If pressure washing: 1,000-1,500 PSI max, 40° nozzle only, spray downward only (never upward), stay 3+ feet away
• Detergent: Roof cleaner with mildewcide. Let dwell 15-20 minutes. Light rinse only.
• Safety: Hire professional for roof cleaning—fall risk is high. Wet shingles extremely slippery.
• Best practice: Soft wash (chemical only, minimal pressure) by professional

Tools, Accessories, and Pressure Washer Maintenance

Essential Tools & Accessories

Pressure washer (appropriate PSI for your needs)
Complete nozzle set (0°, 15°, 25°, 40°, soap)
Turbo/rotating nozzle (optional, for concrete)
Extension wand (reaches high areas safely)
Surface cleaner attachment (for large flat areas)
Soft wash nozzles (for roof cleaning)
Pressure washer detergents (various types)
Safety glasses and closed-toe shoes
Chemical-resistant gloves
Garden hose with good flow rate

Maintenance Tips

Flush pump after every use (run clean water through detergent system)
Release pressure before storage (trigger gun, relieve hose pressure)
Use pump saver/antifreeze for winter storage (prevents freeze damage)
Change oil in gas models per manufacturer schedule
Clean/replace water inlet filter regularly
Inspect nozzles for wear—replace if spray pattern changes
Check hoses for cracks, leaks, damage before each use
Never run pump without water (burns seals)
Store indoors or covered (protect from elements)
Use fuel stabilizer for gas models (prevents carburetor issues)

Critical Safety Warnings

Injection Injuries: Pressure washers can inject water under skin, causing serious medical emergencies requiring immediate surgery. Never point at people, pets, or yourself. Never spray hands or feet (even through shoes). Maintain proper distance from nozzle. These injuries may appear minor but can lead to amputation if untreated.

Electrical Hazards: Water and electricity are lethal combination. Never spray electrical panels, outlets, fixtures, meters, or overhead power lines. Turn off outdoor electrical circuits when pressure washing near outlets. Assume all wires are live. Maintain 10+ feet from power lines.

Fall Hazards: Wet surfaces are extremely slippery. Pressure washer kickback can knock you off balance. Never use from ladder—use extension wand instead. Wear non-slip shoes. Be aware of kickback when pulling trigger. Roofs are especially dangerous when wet.

Chemical Exposure: Detergents and cleaners can cause skin/eye irritation or burns. Always wear safety glasses—splashback is common and unpredictable. Wear gloves when handling concentrated chemicals. Never mix chemicals (bleach + ammonia = toxic gas). Rinse skin immediately if exposed.

Carbon Monoxide (Gas Models): Gas pressure washers produce carbon monoxide—a deadly, odorless gas. Never run gas pressure washer indoors, in garage, or in any enclosed space. Always operate outdoors in well-ventilated area. CO poisoning can cause death within minutes.

Note: Pressure washers are powerful tools that can cause serious injury, property damage, and environmental harm if misused. This guide provides general information—always read your specific pressure washer's manual and follow manufacturer safety instructions. When in doubt about a surface or technique, consult a professional or test on hidden area first. Some surfaces should never be pressure washed—hire professionals for roofs, historic materials, delicate surfaces, and high/dangerous areas.

Quick Reference Summary

Golden Rules

Start wide angle (low pressure), increase only if needed
Test on hidden area first, every time
Keep moving—never hold nozzle in one spot
Soap bottom to top, rinse top to bottom
Match nozzle and pressure to surface hardness

Quick Nozzle Guide

Red (0°): Danger zone—extreme caution only
Yellow (15°): Concrete, heavy stains only
Green (25°): General purpose—most common
White (40°): Delicate surfaces, windows, cars
Black (soap): Detergent application only

Disclaimer: This guide provides general information about pressure washing techniques and safety. Pressure washers are powerful tools capable of causing serious injury and property damage. Surface materials, conditions, and appropriate cleaning methods vary widely. Some surfaces should not be pressure washed at all. Manufacturer instructions for your specific equipment supersede this general guidance. When in doubt, hire a professional pressure washing service. Improperly cleaned surfaces may require expensive repairs or replacement.