Pressure washing guides
The correct method is: identify the surface, pick the lowest pressure that works, apply a cleaning solution and let it dwell, then rinse. ARMA's roof method is a 50:50 laundry-strength bleach and water solution, 15 to 20 minutes of dwell, then a thorough rinse with low pressure water. For wood, Today's Homeowner recommends 1,200 to 1,500 PSI with a wide-angle nozzle about two feet away at a 45-degree angle. Fixr recommends 1,500 PSI for wood and composite decking.
Chemistry does the cleaning; water removes it. On anything organic - algae, mildew, moss - the solution and its dwell time do the work. Today's Homeowner's mixing guidance uses a quarter gallon of chlorine to a gallon of water at roughly 1:9 with a 25 to 30 minute dwell, or a quarter gallon of bleach to a gallon of water with a 15 to 30 minute dwell. ARMA's roof method is a 50:50 bleach and water mix with a 15 to 20 minute dwell, rinsed with low pressure water. If a crew is not letting anything dwell, they are relying on pressure instead.
Pressure by surface. Fixr's fence figures give a useful ladder: softwoods like pine and cedar 500 to 600 PSI, hardwoods 1,200 to 1,500, composite under 1,500, aluminum under 1,800, steel 1,800 to 2,000, wrought iron under 2,300. Its house data notes the range runs from around 500 PSI for brick to 3,500 for concrete, and its deck guidance sets wood and composite at 1,500 PSI. Today's Homeowner treats anything above 2,000 PSI as excessive for wood.
Technique. Distance and angle matter as much as the dial. Today's Homeowner recommends a wide-angle nozzle about two feet from cedar siding at a 45-degree angle. Polymeric Exteriors guidance says to hold the washer straight at eye level on vinyl siding and not aim upward, because that forces water behind the panels. NPS guidance on masonry notes that nozzle distance and flow rate significantly affect the outcome, and gives the field test: stone grains or sand in the runoff means the pressure is too high.
Preparation. ARMA advises protecting landscaping from the bleach solution. NPS advises confirming mortar joints are sound and the building is watertight before any water cleaning, because otherwise water seeps through the wall and damages interior finishes. Both of those checks happen before anyone turns a machine on.
Steam and hot water. NPS describes steam cleaning as effectively low-pressure hot water washing - its example shows under 100 psi - and calls it a gentle, effective method for stone, particularly acid-sensitive stone. Heat is a tool for grease and stubborn deposits, not a shortcut for using less care.
Choosing pressure washing an approach
The judgement calls that decide the bill, before anyone quotes you.
- Judge a crew by whether they let solution dwell Apply, wait, rinse. If they're spraying and immediately blasting, they're cleaning with pressure and that's what damages surfaces.
- Ask for the PSI they'll use, surface by surface There should be a different number for concrete, brick, siding, wood and composite. One number for the whole job is a warning sign.
- Watch the nozzle angle and distance Wide-angle tip, appropriate distance, never angled up under siding or shingles. Close-in narrow tips are where the damage happens.
- Insist on plant and opening protection first Landscaping covered or pre-wet, windows and doors accounted for, electrical fixtures avoided. This should happen before mixing, not after.
- Start low and step up Test in a hidden area at the low end of the range. You can always add pressure; you cannot take etching back out of brick.
All pressure washing guides
Pressure Washing Planning Guide
House Washing Guide
Soft Washing Guide
Driveway Cleaning Guide
Deck Cleaning Guide
Siding Safe Cleaning Guide
Pressure Washing Safety Guide
Hiring a Pressure Washing Company
Seasonal Exterior Cleaning Guide
Curb Appeal Pre Sale Cleaning Guide
Climate and Exterior Dirt Guide
Water Restrictions and Pressure Washing
Where these figures come from
Sources last checked
- ARMA - Algae and Moss Prevention and Cleaning of Asphalt Roofing Systems · retrieved 2026-07-26
- Fixr - Cost to Pressure Wash a Fence (PSI by material) · retrieved 2026-07-26
- Fixr - Cost to Pressure Wash a Deck (PSI guidance) · retrieved 2026-07-26
- Fixr - Cost to Pressure Wash a House (PSI range) · retrieved 2026-07-26
- Today's Homeowner - Pressure Washing Cedar Siding · retrieved 2026-07-26
- Today's Homeowner - Chlorine vs Bleach for Pressure Washing · retrieved 2026-07-26
- NPS Preservation Brief 1 - Cleaning and Water-Repellent Treatments for Historic Masonry (PDF) · retrieved 2026-07-26
- Polymeric Exteriors Association - Cleaning · retrieved 2026-07-26
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