Composite Deck Cleaning: What the Manufacturer’s Guide Should Tell You
There is no composite deck cleaning method. There is your board’s method, and the maker wrote it down. Four answers decide the work: whether a washer is permitted and at what ceiling, which brush, which cleaner class, and what the warranty excludes.
The three makers read for this page publish four pressure figures between them — 1,500 psi, 2,500 psi, 3,000 psi and 3,100 psi — and two different brushes for boards all marketed as composite. The bottle in the shed is labelled for a material, and that word may not be the material on your deck. The deck and fence guide owns the prior question, whether the structure is worth cleaning; this page owns what the maker permits.
Two materials, and one misleading word
“Composite” covers at least three different things: an uncapped wood-plastic composite, a capped one, and a solid PVC board. They do not take the same cleaner, and the difference is published.
TimberTech states that the capping material on its current products “is not composed of a wood/plastic composite”, and instructs that composite deck cleaners — it names several by brand — should not be used on them. AZEK’s installation guide is blunter about its PVC decking: “AZEK Deck is a PVC/polymer deck plank and not a wood/plastic composite”, and composite deck cleaners “SHOULD NOT be used” with it.
Meanwhile the makers selling wood-plastic composites recommend that class of product: one directs a composite deck cleaner for its early-generation boards and a deck brightener, containing oxalic acid, for tannins.
So the first question is not what is growing on the boards. It is what the boards are, which collection they belong to, and whether it is capped. The collection name is on a board edge or the original paperwork; the maker’s current guide is on the maker’s site, and it governs the warranty.
| The guide has to answer | Why it changes the work |
|---|---|
| Is a washer permitted, at what ceiling, at what distance? | Four published ceilings between 1,500 and 3,100 psi, and one maker permits a washer for rinsing only |
| Which brush? | One maker specifies stiff natural fibre for its PVC boards and medium-to-stiff nylon for its composite boards |
| Which cleaner class, dilution and dwell? | Capped and PVC boards reject cleaners that uncapped composite needs; dwell and rinsing decide whether a film is left |
| What voids the warranty, and what has a deadline? | One maker allows seven days on a food spill; another voids coverage for damage a washer causes |
The pressure question: three makers, four numbers
None of these figures is a target.
| Maker’s document | Published limit |
|---|---|
| Trex, care page | No greater than 3,100 psi, fan tip no closer than 8 in (203 mm), with soap; the maker does not recommend a pressure washer on its early-generation boards, and damage one causes voids coverage |
| TimberTech, care page and installation guide | Maximum 1,500 psi, fan tip, spray with the grain and never across it — and a power washer is for rinsing only |
| Fiberon, general FAQ and maintenance page | Under 3,000 psi, wide fan tip, 12 in above the deck (FAQ) or 10 in (maintenance page) |
| Fiberon, care article | Less than 2,500 psi at 12 in above the deck |
The same maker publishes three distances and two ceilings across three of its own pages: the figure you find is the figure in the document you happened to open, not a property of composite decking.
Two rules survive the disagreement. None of these documents describes pressure at the surface; each pairs its figure with a fan tip and a stand-off distance, so the number alone does not say what reaches the board. And a ceiling is a limit, not an instruction.
Two cautions come from the makers. Fiberon states that pressure washing is not recommended where mold or mildew is present, because the pressure drives it further into the pores, and that improper use voids warranty coverage. TimberTech permits the machine for rinsing only. Where a washer is restricted to rinsing, a garden hose does the same work.
Brushes: the cap decides
The same company that warns against a stiff natural-fibre brush on its composite boards tells you to use one on its PVC boards. TimberTech lists a stiff natural-fibre brush for its Advanced PVC decking and a medium-to-stiff nylon brush for its composite collections, warning that a stiff natural-fibre brush “can dull the surface” of the composite.
Trex asks for a soft bristle brush and warm soapy water. Fiberon asks for a non-metal scrub brush, and states that metal shovels or sharp-edged tools should never be used to clear ice from its boards.
The rule underneath is about the surface. A capped or PVC board carries a thin cosmetic skin; a bristle stiff enough to scour dirt out of an embossed grain also scuffs that skin. An uncapped composite has no skin to lose. Buy the brush the guide names, not the one the shelf calls a deck brush.
Cleaner, dwell, and the film that will not rinse out
All three makers name one failure: cleaner or dirty water left to dry on the boards. Trex states that dirty water left to dry leaves a film. TimberTech states that a cleaner allowed to dry causes a white film that can be difficult to remove. Fiberon asks for small sections, the decking kept wet throughout, and each section rinsed completely.
TimberTech publishes the working numbers: dilute one part cleaner to three parts water, saturate the area, let it stand 30 to 60 seconds, scrub with the recommended brush and rinse immediately — roughly one gallon of solution to 1,000 square feet. It also states not to clean in direct sunlight, because the heat dries the surface before the rinse arrives.
In practice, all decking gets hot in the sun, TimberTech notes, and darker colours feel hotter, so a board in full afternoon sun works against you. Its warning goes further than cleaning. Sunlight reflected from low-emissivity windows can raise surface temperatures far above normal exposure and melt, sag, warp or discolour decking, and hot debris from cutting metal on the deck can become embedded in it. If a patch has distorted with no cleaner near it, establish the cause before cleaning it again.
Never mix products. Fiberon states the rule without qualification, adding that bleach must never be mixed with acids. One maker’s guide notes that bleach or acid will lighten the surface, and asks for a test in an inconspicuous area first.
Stains that are not dirt
Most marks are one of six things, and the remedy differs by maker as well as by stain.
| What it is | What the makers publish |
|---|---|
| Tannin or extractive bleed, brown streaking near a damp edge | TimberTech states it weathers away with rain and UV, usually in 8 to 10 weeks, and can also be cleaned; Trex directs a deck brightener containing oxalic acid |
| Hard-water spotting, white where tap or sprinkler water dried | Trex directs white vinegar and thorough rinsing, warns against rinsing with hard water, and suggests a brightener where vinegar fails |
| Rust or metal marks | AZEK directs a rust-removing household cleaner |
| Oil, grease and food | Trex states the surface must be cleaned within seven days to maintain the stain warranty; Fiberon suggests an all-purpose cleaner or one formulated for the decking type |
| Concrete, mortar or stucco dust | Trex asks that decking be protected during masonry work, stating the particles can react with the surface once hot or wet; TimberTech asks that masonry not be cut on or near the deck |
| Sunscreen and insect repellent | TimberTech and Fiberon both warn these can alter or stain the surface and ask the reader to check labels and keep application off the boards |
Three more marks come from things left on the deck. All three makers warn that rubber-, vinyl- or latex-backed mats can discolour the surface, and point to colourfast woven or polypropylene mats instead. Flower pots and anything else sitting flat block evaporation and can stain, Fiberon states. One maker warns that PVC glue or solvent on the surface discolours it permanently.
Ice, snow, and a second disagreement
Where a deck carries snow and ice through the winter, the de-icer question returns every year, and the makers split on it. All three read here permit a calcium chloride-based melt. Trex and Fiberon also permit rock salt; TimberTech instructs the reader to avoid rock salt and other abrasive ice-melt products.
Fiberon adds two rules: never use sand, because the abrasion grinds into the surface, and avoid ice melt with an added colourant, because the dye can stain.
Two points hold. Metal shovels, and plastic shovels with a metal leading edge, can damage the surface. And the residue the melt leaves is cleaned with water and light scrubbing, not a pressure washer, Fiberon states directly.
What cleaning will not fix
Cleaning restores a surface; it does not repair one. A chip, a gouge, a scratch, a board faded unevenly, a board lifted at a butt joint, a loosened stair nosing — none is a stain, and no cleaner addresses them. One maker publishes a separate chip-and-scratch repair bulletin, which is the point: a chip is a repair with its own method.
Sealers are the other false remedy. Fiberon states that its products require only periodic cleaning and that deck sealants are not required or recommended. Sanding is not a remedy either: Trex states that it does not recommend sanding, that sanding changes the surface’s appearance, and that it voids the warranty for any condition the sanding caused.
Structural symptoms — movement underfoot, a loose guard, a ledger pulling away, soft material at a post base — come before any surface work, and belong to the deck and fence guide.
The next useful action
Write down the product line and collection, open the maker’s current care document, and answer the four questions above. Test the cleaner in a corner. Work out of direct sun, in sections small enough to keep wet, with the brush the guide names. Rinse until the water runs clear, and let the boards dry before anything else goes on them.
Then deal with where the water went. Rinse water carrying a cleaner is not the same as rain, and in Washington what is allowed is decided locally; the wash-water page works through it.