What PSI Should You Use on a Pressure-Treated Deck?
- Stay on the lower end if the wood is older, weathered, or has been exposed for several years
- Avoid going higher just because the wood is "treated" — the chemical treatment doesn't prevent surface damage from too much force
- Going above 1,500 PSI is when most people start seeing fuzzing, gouging, and stripped fibers
How Do You Prep a Deck Before Pressure Washing?
- Sweep away leaves, dirt, and debris
- Move furniture, planters, and rugs off the deck
- Check for loose boards, popped nails, or splintered wood that could worsen under pressure
- Cover or wet down nearby plants and grass to protect them from runoff
What Nozzle and Distance Should You Use?
- Use a 25–40 degree fan tip, never a narrow jet (a 0-degree "pencil jet" will tear up wood fibers almost instantly)
- Keep the nozzle 8–12 inches from the surface
- Avoid lingering in one spot — this is the #1 cause of gouging and etching
Why Spraying With the Grain Matters
- Hold the nozzle at roughly a 45-degree angle
- Move in smooth, overlapping passes following the direction of the wood grain
- Don't spray straight down or across the grain at high pressure — this drives water into the wood and tears up fibers, leading to that "fuzzy" raised-grain look
How Do You Remove Mildew and Graying Before Rinsing?
- Apply a deck cleaner with mild bleach or oxygen bleach (sodium percarbonate) to lift mildew, algae, and gray, weathered wood
- Let it sit for 10–15 minutes (check product label) before rinsing
- This reduces how much pressure you need for a clean result, which means less risk to the wood
Which Areas of the Deck Need Extra Care?
- Newer pressure-treated wood (under 1 year old) — it's softer and more prone to fiber damage
- Joints, screws, and nail heads — high pressure can drive water into gaps and cause swelling
- Railings and balusters — thinner and more fragile than deck boards
Should You Test a Spot First?
Yes. Try your settings on a small, hidden section before tackling the whole deck. Check that you’re not stripping wood fibers or removing existing stain/sealant too aggressively. This takes five minutes and can save you from redoing an entire deck’s finish.
How Long Should You Wait Before Sealing?
Allow at least 48 hours of drying time before applying stain or sealant. Pressure-treated wood holds more moisture than other woods, so don’t rush this step — sealing over damp wood can trap moisture and lead to peeling or mold underneath the finish.
Once dry, apply a water-repellent sealant, since washing strips away any existing protective coating.
PSI Recommendations by
Deck Material
|
Material
 |
Recommended PSI
 |
Nozzle
 |
Notes
 |
|---|---|---|---|
|
Pressure-treated wood  |
1,000–1,500 |
25–40° fan |
Tougher than cedar/redwood, but still prone to fuzzing above 1,500 PSI |
|
Cedar / redwood  |
500–1,200 |
25–40° fan |
Softer wood, more prone to gouging |
|
Composite decking  |
500–1,200 |
40° fan |
Check manufacturer guidelines — some void warranty above certain PSI |
|
Concrete  |
3,000+ |
15–25° fan |
Much higher tolerance, not comparable to wood |
Quick Reference Glossary
PSI (pounds per square inch)
A measure of water pressure output from the washer. Higher PSI means more force.
Fan tip / fan nozzle
A nozzle that spreads water into a wide spray pattern, reducing the concentration of force on any one spot.
Oxygen bleach (sodium percarbonate)
A cleaning agent that breaks down mildew and algae without the harshness of chlorine bleach, safer for wood and surrounding plants.
Fuzzing
When pressure washing raises and roughens the wood grain, leaving a fuzzy texture on the surface.
Bottom Line
Not Comfortable Doing It Yourself?
Pressure washing a deck the right way takes the correct equipment, the right cleaning solution, and a steady hand. If you’d rather leave it to the pros, Grato Property Care offers professional deck and pressure washing services throughout Irwin, Greensburg, and Pittsburgh. We use the right PSI and technique for pressure-treated wood, so your deck gets clean without the risk of damage.
Learn more about Grato Property Care or reach out to schedule a free estimate for your deck.
