Pressure washers blast away dirt, mildew, and old paint from siding, decks, driveways, and patio furniture. The water pressure (1500-3000+ PSI) does the cleaning. The wrong nozzle or technique causes real damage: stripped paint, splintered wood, eroded grout, and serious injury (skin lacerations are surprisingly common). Used correctly, pressure washers cut hours off cleaning time and prep surfaces for painting.

This guide covers electric and gas pressure washers for typical residential exterior cleaning.

Before you start

Three things to settle:

1. PSI matters per surface. 1500-1900 PSI: cars, decks, patio furniture, vinyl siding. 2000-2800: concrete, hard surfaces, paint stripping. 3000+: industrial use, masonry, heavy-duty cleaning. More isn't better — high PSI on softwood erodes the grain.

2. Nozzle colour codes. Red (0°): pinpoint, very narrow stream — paint stripping, can damage almost anything. Yellow (15°): narrow, aggressive — paint stripping, masonry. Green (25°): standard cleaning — most surfaces. White (40°): wide, gentle — cars, vinyl, wood. Black: low-pressure, soap detergent application.

3. Don't point at people, pets, or yourself. 0° (red) nozzle at close range can lacerate skin and inject water under skin (medical emergency). 15° (yellow) is dangerous too. Even gentler nozzles cause eye injury at close range. Always away from people.

What you'll need

Tools

Pressure washer (electric 1500-2000 PSI or gas 2500-3200 PSI)
Garden hose (for water supply)
Spray gun and lance (typically included)
Variety of nozzles or adjustable nozzle

Materials

Pressure washer detergent (for soap-applying)
CSA safety glasses
Closed-toe non-slip footwear
Long pants and long-sleeve shirt
Hearing protection (gas units are loud)
Optional: surface cleaner attachment (for driveways)

Start with the gentlest nozzle and work up

When uncertain about a surface: start with white (40°) at maximum stand-off distance (3+ ft).

If cleaning is too slow: shorten distance OR step up to green (25°). Don't jump to yellow or red without testing.

Step-by-step instructions

Connect water supply

Attach garden hose to pressure washer's water inlet.

Open the water spigot fully — pressure washer needs continuous flow.

Pull trigger on spray gun for a few seconds to clear air from the system.

Connect spray gun and lance, install nozzle

Connect quick-connect spray gun and lance.

Install nozzle: pull collar back on lance, insert nozzle, release.

Verify nozzle is locked in.

Start with white (40°) for testing.

Wear PPE

CSA safety glasses (water + debris flies back).

Closed-toe shoes (water is dirty and pressurized).

Long pants and sleeves (overspray on skin is uncomfortable).

Hearing protection if gas unit.

Start the unit and test on inconspicuous area

Electric: plug in, switch on, pull trigger.

Gas: pull starter cord per manufacturer.

Test on hidden corner of work area: assess cleaning effectiveness without risking visible damage.

Spray technique: 24 inches, smooth passes

Hold nozzle 18-24 inches from surface for moderate cleaning.

Move at steady pace — about 1 ft per second.

Sweep parallel to the surface, not at angles — perpendicular angles drive water under siding or trim.

Overlap passes 30-50% for even cleaning.

Apply detergent if needed

Switch to black detergent nozzle.

Activate detergent siphon per manufacturer instructions.

Apply low-pressure soap, working bottom-up to prevent streaks.

Let dwell 5-10 minutes (don't let dry).

Switch to green or white nozzle to rinse top-down.

Surface-specific technique: vinyl siding

White (40°) nozzle at 18-24 inches.

Direct spray downward at 30-45 degree angle (not upward — drives water behind siding).

Top-down: rinse soap or dirt downward.

Move steadily; don't dwell on one spot.

Surface-specific: decks (be cautious)

Decks are softwood; high pressure splinters and erodes grain.

Use white (40°) at 12-18 inches max — anything closer damages.

Sweep along grain, not across.

After washing: deck must dry 48-72 hours before sealing.

Surface-specific: concrete and driveways

Surface cleaner attachment is best — produces even cleaning, no streaks.

Or: green (25°) at 12 inches in slow passes.

Don't dwell — high PSI on concrete erodes the surface.

Power off and store

Disconnect water supply, run trigger to relieve pressure.

Pull starter cord with engine off OR cycle electric unit briefly to clear water.

In freezing weather: drain unit fully or run RV antifreeze through (frozen water cracks pump).

Common mistakes that cost you

Red (0°) nozzle on residential surfaces. Etches concrete, strips paint, lacerates skin. Use for industrial only.
Spraying upward into siding. Drives water behind siding into wall cavity. Spray downward at 30-45° angle.
Holding nozzle too close. Damage on every surface. 18-24 inches typical.
Pressure washing painted surfaces with high PSI. Strips good paint along with bad. Use moderate pressure if washing painted siding.
Not draining for winter storage. Frozen water cracks pump. Drain or use RV antifreeze.

Frequently asked questions

Electric or gas pressure washer?

Electric (1500-2000 PSI): light to medium duty, quieter, easier to maintain. Great for vinyl, decks, vehicles.

Gas (2500-3200 PSI): heavy duty, more cleaning power, requires more maintenance. Better for driveways, big jobs.

For most homeowner use, electric is enough.

Can I pressure wash my roof?

No — high pressure damages shingles, lifts edges, drives water under flashing.

For moss/algae: use a roof-cleaning solution (like sodium hypochlorite or specialty product) with a low-pressure pump sprayer.

Pressure washing roofs voids most shingle warranties.

How often should I pressure wash my deck?

Once a year for cleaning and prep before re-staining.

Use lowest effective PSI and white (40°) nozzle.

Wait 48-72 hours for deck to dry before staining or sealing.

When to call us instead

Exterior cleaning and prep is part of our exterior renovation work. We pressure wash before painting, staining, or re-cladding.

Book a free 60-minute site visit →

Related Ottawa services

If your renovation includes exterior work, our team handles cleaning, prep, and finish. Book a free 60-minute consultation.