Wood is the easiest surface on a property to ruin with a pressure washer, and a furred, splintered deck is the most common way it happens. Proper deck and fence cleaning is chemistry first, low pressure second — in that order, always.
Why wood tears
Timber is not uniformly hard. Softwood decking alternates dense latewood grain with much softer earlywood, and a pressure stream erodes the soft bands far faster than the hard ones. Push too much pressure — or hold the tip too close — and you carve the soft grain out, leaving raised ridges, fuzz and splinters.
The reason sits in how the tree grew. Every annual ring is two bands. Earlywood is laid down fast in spring, with wide, thin-walled cells and a lot of air in it. Latewood is laid down slowly late in the season, with narrow, thick-walled cells packed tight — it is the dark line you can see running across the end of a board. Earlywood is lighter, more porous and mechanically weaker in every direction. A water jet does not distinguish between grain and grime; it removes whatever resists it least, and that is always the earlywood.
What you are left with is a washboard: latewood ridges standing proud, earlywood troughs cut between them, and severed fibres standing upright out of the surface. Those upright fibres are the fuzz. They hold water instead of shedding it, they trap dirt, and they find bare feet.
Once the grain is torn, washing cannot fix it. The repair is sanding, which on a full deck is a serious project. Prevention is the entire game.
Species changes how much room you have
The same tip at the same distance behaves differently on different boards, and the difference is density contrast rather than hardness alone.
Pressure-treated southern yellow pine — the standard deck board across this region — has the steepest contrast between its soft and hard bands of anything you are likely to be standing on. That is exactly the condition that produces ridging, so treated pine furs at pressures that would leave other timbers untouched. It is also the timber most often washed by someone who has just rented a machine, which is why treated pine decks account for most of the damage we are asked to look at.
Cedar is soft throughout rather than banded. It does not ridge the same way, but it dents and gouges readily, and a stalled wand leaves a permanent shadow on it. Dense tropical hardwoods sit at the other end: they tolerate more force, but they are oily, they grey uniformly rather than in patches, and they want a gentler chemistry and a longer dwell rather than a stronger one. Knowing which of the three you own tells you where the ceiling is before anyone starts.
The sequence that works
A percarbonate or hypochlorite-based deck cleaner goes on first and does the actual work: breaking down the grey oxidised surface layer and killing algae and mildew. After proper dwell time, a wide-fan, low-pressure rinse carries it all away — the water is transport, not the tool.
Percarbonate or hypochlorite
Both are alkaline, and they solve different problems. Sodium percarbonate releases hydrogen peroxide in solution — oxygen bleach. It is the right call when the complaint is colour: the flat grey layer of oxidised, UV-degraded surface wood that makes a sound deck look dead. It works slowly, wants a longer dwell and a scrub, and it is comparatively easy on the plantings around the deck.
Sodium hypochlorite kills biology fast and thoroughly, which makes it the right call when the deck is genuinely colonised — black mildew, green algae film, shaded boards that never dry. It does less for oxidation and it needs discipline: controlled dilution, plants pre-wet and rinsed, and an eye on anything downhill of the work. Reading a deck properly means deciding whether you are looking at a dead surface layer, a living colony, or both, and mixing accordingly.
Why the brightener is not optional
Badly greyed wood gets a brightener afterwards — usually oxalic acid — which neutralises the cleaner’s alkalinity and pulls the timber’s colour back toward fresh-cut. If staining is planned, the brightening step is not cosmetic: coatings bond poorly to alkaline wood.
Wood sits naturally on the acidic side. An alkaline cleaner pushes it well past that, and alkaline wood darkens, raises its grain and takes finish unevenly. Oxalic acid brings the pH back down and, as a bonus, dissolves the iron tannate stains that show up as blue-black marks around fasteners and as rust runs below hardware. Skipping the brightener is how a deck ends up clean, dull and slightly muddy in colour, and it is one of the reasons a new finish lets go inside a single season.
Reading a deck before touching it
Board condition dictates everything. Sound timber takes the standard process; soft, spongy boards, popped fasteners and wobbling rails mean the deck needs a carpenter before it needs a cleaner.
Age matters too — older, weathered decks have less sound surface to spare, so pressure discipline gets stricter as the wood gets older. A deck that has already been furred once by a previous wash has lost its dense surface fibre and will fuzz again at even lower pressure, so it gets treated as the fragile thing it now is. Where the question is bigger than the finish, work through whether the structure is worth cleaning at all before spending money on the surface.
Fences are the same problem at a different angle
A fence is decking stood on end, and the physics do not change — but three things do.
Grain runs vertically, so damage runs vertically too, and a furred picket sheds splinters at hand height rather than underfoot. Solution runs off a vertical surface instead of sitting on it, so dwell time is short and the work is usually a wetter mix and more passes rather than more pressure. And pickets are thin, often nailed rather than screwed, so the same jet that only marks a deck board can rack a whole panel loose.
Then there is the other side. A fence has two faces and usually two owners. We clean what we can lawfully reach, and if the far side belongs to a neighbour, that is a conversation to have before the day rather than during it — most neighbours say yes when asked in advance, and a fence cleaned on one face only reads as two-tone from the street. Where a shared fence runs alongside a driveway or patio, it is worth pairing the work with the concrete cleaning underneath it, because rinse water off the pickets lands there anyway.
What Southeast Missouri does to a deck
Our decks are shaded, damp and constantly fed. Mature oak and pine cover means spring pollen, then leaf and needle drop, then tannin bleeding out of everything that sits on a board through a wet week. In the river-valley damp around Cape Girardeau and Perryville, morning fog keeps a shaded deck wet into the middle of the day for weeks at a stretch, and a surface that never dries is a surface that grows mould. Those decks lean toward a hypochlorite-led clean; a sun-exposed deck in an open field outside Patton is usually an oxidation problem instead, and percarbonate suits it better.
Freeze-thaw is the reason furring here is not merely ugly. Winter water sits in that torn, upright fibre, freezes, expands and levers the surface apart a little further each cycle — so a deck damaged in July looks appreciably worse by March. Well water matters too: much of the water around Patton, Marble Hill and Fredericktown carries iron, and rinsing a deck with it can leave a faint orange cast on pale timber. That is a brightener problem rather than a scrubbing problem, and it is the same chemistry that lifts the orange staining well water leaves on concrete.
Common questions
Can a deck that has already been furred be saved?
Often, yes — partially. A brightener plus a light sanding of the worst boards knocks the raised fibre down and restores a usable surface, and stain over the top hides a great deal. What sanding cannot do is put the eroded earlywood back, so a deep washboard stays slightly ridged under your hand. That is the honest ceiling.
Will deck cleaner kill the plants around the deck?
Not if the work is managed. Beds get soaked with clean water before the cleaner goes on and rinsed again afterwards, and dilution is set for the job rather than poured strong for speed. Percarbonate is the gentler option where planting is tight against the boards, which is one of the things we look at in your photos.
How long after washing before the deck can be stained?
Roughly forty-eight dry hours, and longer in humid weather. Dry to the touch is not dry through, and a coating applied over trapped moisture fails from underneath. The timing of the whole clean-and-stain sequence is worth planning as one job rather than two.
Are the rotating brush attachments sold for decks any safer?
They are safer than a bare wand in the sense that they hold a fixed standoff distance, but they still put concentrated force on softwood, and the ones with stiff bristles will polish the earlywood out just as effectively over a few passes. The pressure is not the problem in isolation — the problem is force per unit area held in one place.
Does every deck need sanding?
No, and most do not. Sanding is a repair for torn grain, not a routine step. A deck cleaned with chemistry and rinsed at low pressure comes out smooth because nothing tore in the first place, which is precisely why the sequence is worth insisting on.
If a previous wash already furred the surface, ask us to look — sometimes a brightener and light sand rescue it. Read more about deck and fence cleaning →