Wood decks and fences in Miami can be cleaned with a pressure washer, but only at low pressure: most guidance for pressure-treated lumber stays at roughly 800 to 1,200 PSI with a wide fan tip held about a foot or more from the boards. Go harder or closer and the soft surface fibers tear, leaving a fuzzy, streaked finish that holds even more dirt. In this climate the bigger job is usually not the washing but the drying that follows, because wood that is sealed while still damp tends to trap moisture and fail early.
Why wood is a different job from concrete
Concrete and pavers shrug off a strong jet. Wood does not. Its surface is made of fibers running along the grain, and a narrow or close spray lifts them, carves grooves into the softer spring growth and leaves lines that show for years. Miami adds three complications: near-constant humidity, heavy summer rain and strong sun. Together they feed mildew and algae in the shade, gray out the surface in the sun and keep boards damp far longer than in a dry state.
Some sources suggest pressure up to 1,500 PSI is acceptable on certain woods, but those are contractor and retailer blogs rather than independent testing, and they disagree with each other. Treat 1,200 PSI as a sensible ceiling for ordinary pressure-treated pine and start lower on older, softer boards. If your deck is composite, the rules are different; see the manufacturer note below.
What you are actually cleaning off
- Black or green film. Mildew and algae, common on shaded fence panels and north-facing deck boards. The same organisms are covered in our guide to exterior mold and mildew.
- Gray, silvery surface. Sun and rain weathering the top layer of wood. It is cosmetic and often cleans up with a wood brightener.
- Rust-colored spots. Often irrigation water or metal fasteners. Sprinkler overspray on a fence is a frequent source; the same issue on slabs is explained in the driveway stains guide.
- Old stain or sealer. A cleaner made for wood is needed to strip failing finish. Pressure alone usually leaves it patchy.
Pressure, tips and distance
These figures are typical ranges from the sources we reviewed, not rules. Always test a hidden board first.
| Setting | Typical guidance | Why it matters |
|---|---|---|
| Pressure, pressure-treated pine | About 800 to 1,200 PSI | Higher pressure raises fibers and etches soft growth rings |
| Nozzle | Wide fan tip, 25 or 40 degrees | A zero-degree pencil jet can shred wood almost instantly |
| Distance | Roughly 12 to 18 inches | Closer than about a foot tends to fuzz the surface |
| Direction | Along the grain, wand always moving | Lingering in one spot is a leading cause of gouging |
| Composite decking | Follow the manufacturer's care guide | Limits differ by brand and affect warranties |
If you need more cleaning power, increase the distance or switch to a wood cleaner and a soft brush rather than raising the pressure. This is the same logic behind soft washing versus pressure washing on delicate surfaces.
A sensible sequence for a deck or fence
- Check the boards. Probe with a screwdriver. If the tip sinks in, the wood is rotting and cleaning will not fix it.
- Protect plants and fixtures. Wet nearby landscaping first and cover outlets and lights. Cleaners made for wood can harm plants.
- Apply a wood cleaner. Let it work for the time on the label without drying on the surface, usually in shade or on an overcast morning.
- Rinse along the grain at low pressure, working from the top down.
- Brighten if needed. A wood brightener helps restore color and neutralize the cleaner.
- Let it dry fully. This is the step that matters most.
Drying time before you stain or seal
Vendor and contractor sources commonly aim for wood moisture of about 12 to 15 percent before a finish goes on, and recommend a wood moisture meter because a board can feel dry on top while staying wet inside. Typical advice is about 48 hours of drying in good conditions and three to four days in humid weather, so in Miami plan on at least two to four dry days, longer for shaded fences and dense hardwood.
After sealing, the surface may feel dry in 6 to 24 hours, but a full cure takes longer: often several days for water-based products and up to a couple of weeks for heavy oil-based ones. Read the product label, and avoid starting a job when afternoon thunderstorms are forecast. Our hurricane season exterior guide covers the calendar, since the wet season is the hardest time to get a clean dry window.
New pressure-treated lumber is a special case. Recommendations range widely, from a few weeks to several months, before it takes a finish well. A simple test is to sprinkle water on the board: if it soaks in within about a minute, the wood is ready to absorb sealer, and if it beads, wait.
Costs, in general terms
Pricing varies by company, wood condition, access and square footage, and a fence is often quoted by linear foot while a deck is quoted by area. We do not publish a figure here because published numbers vary too widely; see typical pressure washing price ranges for the general picture, and ask any provider whether cleaning, brightening and sealing are quoted separately. Verify any price with the provider.
Mistakes that cost money
- Sealing over damp or dirty wood, which traps moisture and encourages peeling.
- Using high pressure on old, soft boards to speed things up.
- Cleaning a shared fence without checking with the neighbor who also owns or maintains it.
- Skipping repairs: loose boards and rusted fasteners are cheaper to fix before sealing than after.
- Letting wash water run into the street; see the wash water rules.
If a repair goes beyond cleaning, such as replacing a section of fence or rebuilding stairs, check with your city or county building department first, since permit requirements for fences and raised decks depend on the type of structure and the municipality.
Frequently Asked Questions
Can I pressure wash a wood fence in Miami?
Yes, at low pressure. Most guidance for pressure-treated wood is roughly 800 to 1,200 PSI with a wide fan tip about a foot or more away, working along the grain. Test a hidden spot first.
How long should wood dry before I seal it?
Typical advice is at least two to four dry days in Miami's humidity, or until a moisture meter reads about 12 to 15 percent. Shaded areas and dense hardwoods take longer.
Why does my deck turn green so quickly?
Warm temperatures, frequent rain and shade let algae and mildew grow on wood throughout the year. Improving airflow, trimming plants back and cleaning before heavy growth builds up all help.
Is it safe to pressure wash composite decking?
Often, but the limits vary by manufacturer, and exceeding them can void a warranty. Check the brand's care instructions before cleaning.
Should I clean and seal in the same day?
Generally no. Wood needs time to dry after cleaning, and sealing too soon can trap moisture in the boards. Many providers quote cleaning and sealing as separate steps.