How to clean composite decking
Composite does not need sealing, but it does need cleaning, and the cap that makes it stain-resistant is also easy to scratch. The tool you use matters more than the product.
Routine cleaning
Once or twice a year, and more often under trees:
- Clear the surface — leaves, pollen, seed pods.
- Wash with warm water and a mild dish soap, using a soft-bristle brush or a medium-pressure nozzle.
- Rinse thoroughly. Detergent residue attracts dirt.
- Let it dry before walking on it, which takes longer than wood because the surface is non-porous.
A pressure washer is acceptable at low pressure — under 1,500 psi — with a wide fan tip, held at least 12″ from the surface and kept moving. Held close, it will etch the cap, and the mark is permanent.
The three stains people actually get
| Stain | Treatment | What not to do |
|---|---|---|
| Rust (from furniture or fasteners) | Oxalic acid cleaner, dwell, rinse | Do not scrub hard — it spreads into the cap texture |
| Grease or oil | Degreaser, then dish soap | Do not use solvent, which dulls the cap |
| Mildew or tannin | Oxygen bleach (sodium percarbonate), not chlorine | Chlorine bleach can lighten the colour permanently |
For anything stubborn, test in an inconspicuous corner first. Composite colour is in the cap, and a cleaner strong enough to remove a stain can also remove the colour.
What scratches it permanently
- Wire brushes and stiff bristle brushes. They leave a dull patch that does not come back.
- Steel wool. Leaves embedded fragments that rust.
- Snow shovels with a metal edge. The single most common cause of a scratched composite deck. Use a plastic-edge shovel.
- Dragging furniture. Felt pads on every leg, and lift rather than drag.
- Pressure washer at close range, as above.
Scratches in a capped board cannot be sanded out, because sanding removes the cap and exposes the core, which is a different colour and absorbs water. This is the single biggest practical difference between composite and wood.
Mould, and why composite still gets it
Composite does not feed mould the way wood does, but pollen, dirt and sap sit on the surface and mould grows on that. Shaded decks in humid climates get it worst. Oxygen bleach and a soft brush handle it; the goal is removing the food source, which is the dirt, not treating the board.
Winter
- Clear snow with a plastic shovel, not metal.
- Avoid de-icing salt where possible; calcium chloride is less damaging than rock salt but both can leave residue.
- Do not use an ice chipper. It will gouge the surface.
What this page leaves out
- It does not cover PVC, which cleans similarly but scratches more easily.
- It does not recommend brands; formulations change.
- It does not cover refinishing, which is not possible on composite.
- It does not cover installation defects such as telegraphing joist lines, which look like dirt but are not.
Questions people actually ask
Can I pressure wash composite decking?
Yes, at low pressure — under 1,500 psi with a wide fan tip held at least a foot away. Held close it etches the cap, and the damage is permanent.
How do I remove rust stains from composite decking?
Oxalic acid cleaner, applied and left to dwell, then rinsed. Do not scrub hard, because it works the rust into the cap texture.
Can scratches be sanded out of composite decking?
No. Sanding removes the coloured cap and exposes a different-coloured core that also absorbs water. Prevention — felt pads, plastic shovels — is the only real strategy.
Does composite decking get mould?
It grows on dirt and pollen sitting on the surface, not on the board itself. Cleaning removes the food source; oxygen bleach handles what is already there.