Clean timber at 500 to 1,200 PSI with a 25–40° tip — far lower than most people assume, and lower than any driveway setting. Wood is soft, and Florida weathering makes the surface fibres softer still. Go above that and you tear the soft spring wood out from between the grain lines, leaving a raised, furry texture that no stain hides and sanding rarely fully recovers.
Below: the right pressure by material, why timber goes grey in the first place, the two-product method, the steps, composite and vinyl, and what to do before you stain.
The right pressure for wood
The mistake is treating a deck like a driveway. Concrete wants force. Wood wants chemistry and a gentle rinse.
| Material | PSI | Tip | Notes |
|---|---|---|---|
| Softwood decking (pine, cedar) | 500 – 800 | 40° | Most Jacksonville decks. 12 in. back, with the grain. |
| Pressure-treated pine fencing | 800 – 1,200 | 25–40° | Harder than deck boards but still furs if you linger. |
| Hardwood (ipe, mahogany) | 800 – 1,200 | 25° | Dense, but shows wand marks readily. |
| Composite decking | 500 – 1,000 | 40° | Clean cold. Heat and harsh chemicals cause chalking. |
| Vinyl fencing | Under 1,000 | 40° | Soft wash usually enough — the green film wipes off. |
| Aluminium / wrought iron | Under 1,200 | 25–40° | Check for loose paint and existing rust first. |
| Cedar shake siding | 500 – 800 | 40° | The most delicate — common in Atlantic Beach. |
Three habits matter as much as the number: keep at least 12 inches back, always move along the grain rather than across it, and never stop moving with the trigger down.
Why timber goes grey
Grey wood isn't dirty. It's oxidised.
UV breaks down lignin — the compound binding the wood fibres together — in the top fraction of a millimetre. Those degraded fibres go silver-grey and lose their bond with the wood beneath. That's why grey timber feels slightly rough and why a hard blast removes the greyby removing the wood.
Understanding that changes the approach entirely. You aren't trying to wash something off. You're trying to break down and lift a degraded surface layer chemically, then rinse it away with as little force as possible.
Alongside the oxidation you'll usually have mildew and algae, especially on the shaded side of a fence or under a tree. Same organism as on house siding, same solution.
The two-product method
This is the part most DIY jobs miss, and it's why professional results look even rather than patchy.
Step one — the cleaner. Either a sodium percarbonate (oxygen bleach) or a dilute sodium hypochlorite solution with a surfactant. Percarbonate is gentler on the wood and better on oxidation; hypochlorite is stronger on mildew. Apply, dwell 10–15 minutes, don't let it dry.
Step two — the brightener. An oxalic-acid based wood brightener. This does two jobs: it neutralises the alkaline cleaner and returns the wood to a neutral pH, and it chemically reverses the darkening that cleaners cause, pulling the colour back toward the natural tone.
Skip the brightener and you get a deck that's clean but washed-out and slightly blotchy, with a raised pH that will interfere with any stain you apply. It's a cheap product and it's the single biggest visual difference between an amateur and a professional result.
Step by step
- Sweep and clear. Move furniture and planters. Check for protruding nails or screws and loose boards — flag anything that needs a repair before you wet it.
- Pre-wet planting around and beneath the deck or fence, and the lawn line.
- Wet the timber with plain water so the cleaner absorbs evenly instead of soaking into dry patches.
- Apply the cleaner, dwell 10–15 minutes, re-wetting if it starts to dry.
- Rinse at low pressure, 40° tip, 12 inches back, moving along the grain in long overlapping strokes. Follow each board end to end rather than working across.
- Apply the brightener to the still-damp wood, leave a few minutes, rinse.
- Rinse the planting again and let the timber dry.
For fencing, do both faces if you can reach them. Cleaning only the side you see leaves the shaded side as a reservoir of mildew that recolonises the clean face.
Composite and vinyl
Both are easier than timber, with one trap each.
Composite decking — clean cold, under 1,000 PSI, with a 40° tip and a mild detergent. The trap is heat and harsh chemicals: hot water and strong solvents cause chalking and can void some composite warranties. Most composite only needs a wash and a rinse. Note that older composite does develop genuine surface mould in Florida shade, which needs a hypochlorite solution, not scrubbing.
Vinyl fencing — a soft wash is normally enough. The green film builds on the shaded side and lifts with solution and a low-pressure rinse. The trap here is pressure at the joints: vinyl fence panels are usually a friction fit into the posts, and high pressure can pop them apart.
Before you stain or seal
Wait 48 to 72 hours of dry weather. This is the most common mistake on Jacksonville decks and the most expensive one, because fixing it means stripping a failed finish before you can start again.
Freshly cleaned timber holds a lot of water, and our humidity means it releases it slowly. Seal too early and you trap moisture under the film. The coating peels within a season.
The test takes ten seconds: sprinkle water on the boards. If it beads and sits, the wood is still saturated and can't accept a finish. If it soaks straight in, you're ready.
Two other things worth knowing:
- Brand-new pressure-treated timber needs longer — often several months — before it will accept a stain, because it's still wet from the treatment process.
- Don't stain in direct summer sun. The finish flashes off before it penetrates and you get lap marks.
My honest take
Decks are where I see the most avoidable damage, and it's almost always someone who did a great job on their driveway last weekend and used the same setup on the deck the following weekend. The settings that make concrete look brilliant will wreck a pine board in about two seconds.
If you do one thing differently after reading this: buy the brightener. It costs about $25, it takes five extra minutes, and it's the difference between a deck that looks cleaned and one that looks restored.
Honest opinion on fences: cleaning both faces genuinely costs close to double, and for a lot of properties it isn't worth it. If the far side faces a neighbour's shed and nobody looks at it, clean the side you see and accept slightly faster regrowth. We'll quote it either way and we'll tell you when we think the cheaper option is fine.
Full detail on our deck and fence cleaning service, or see how it compares to everything else in the Jacksonville price guide. To get a fixed price for your own deck, send us the dimensions.
