Pressure Washing
What PSI to Pressure Wash a Composite Deck (1,000 to 1,500)
Quick answer
Composite decking takes 1,000 to 1,500 PSI and about 1.2 GPM with a 40 degree fan held 8 to 12 inches away. Check your decking brand first: several makers cap pressure or warn that pressure washing voids the warranty. A 250 square foot deck takes about 69 minutes at 1.2 GPM.
Composite and PVC boards do not gouge the way pine does, but they are not indestructible either. The capped surface layer is what gives the board its stain resistance and color, and grinding at it with high pressure leaves dull patches you cannot sand out the way you can with wood. Some manufacturers publish a maximum pressure, and some say pressure washing can void the warranty.
Look up your board brand before you start, then size the job in the pressure washer PSI calculator. The comparison with real wood is in what PSI a wood deck takes.
On this page
What PSI is safe on composite decking?
| Setting | Composite deck |
|---|---|
| Pressure | 1,000 to 1,500 PSI |
| Minimum flow | 1.2 GPM |
| Nozzle | 40 degree fan |
| Distance from the surface | 8 to 12 in |
| Cleaning rate | About 3 sq ft per minute for each 1 GPM |
| Surface cleaner | No |
| Detergent | A composite deck cleaner, or soap and water on a soft brush |
| Watch for | Maker limits on pressure, and warranty language about pressure washing |
Some composite and PVC decking makers limit pressure or warn that pressure washing can void the warranty. Read your decking maker's care guide first; it overrides anything here.
Which nozzle should I use on composite boards?
| Tip | Color | Use on composite |
|---|---|---|
| 40 degree | White | The only tip to use. Wide fan, kept moving along the board. |
| 65 degree or soap | Black | Applies composite deck cleaner at low pressure, which is where most of the cleaning happens. |
Narrower tips concentrate pressure on the capped surface and can leave permanent dull streaks that no amount of cleaning brings back. A 0 degree tip has no use on any deck.
How long does it take to clean a composite deck?
| Deck size | 1.2 GPM | 1.5 GPM | 2.0 GPM |
|---|---|---|---|
| 150 sq ft (10 x 15) | 42 min | 33 min | 25 min |
| 250 sq ft (12 x 20) | 69 min | 56 min | 42 min |
| 400 sq ft (16 x 25) | 111 min | 89 min | 67 min |
| 600 sq ft (20 x 30) | 167 min | 133 min | 100 min |
Minutes = area divided by (GPM x 3 square feet per minute per GPM), the same formula the pressure washer PSI calculator uses. Heavy staining, mildew and detergent dwell time add to every figure, and a pass with detergent plus a rinse pass doubles the wand time.
How do I clean a composite deck step by step?
- Find your decking brand. Look for the brand on a leftover board, the build receipt or the underside of a step, then read that maker's care page for a pressure limit before you set up.
- Sweep the gaps. Clear leaves and grit from between the boards. Trapped debris holds moisture, which is what feeds the mold that shows up as black speckling.
- Wet the deck and apply cleaner. Rinse first so the cleaner spreads, then apply a composite-safe cleaner with the soap tip or a pump sprayer and let it dwell per the label.
- Rinse with the 40 degree tip. Hold 8 to 12 inches off the boards and work along the board length, overlapping passes so there are no lines where you stopped.
- Spot-treat what remains. Grease and berry stains usually need a soft brush and cleaner rather than more pressure. Rinse again afterward so nothing dries on the surface.
Does pressure washing void a composite deck warranty?
It can, which is why this page starts with the manufacturer's care guide. Composite warranties usually cover staining and fading of the capped surface, and makers protect themselves against damage caused by equipment they did not recommend. Language varies by brand: some publish a maximum PSI and a minimum nozzle distance, some ask for a soft brush and soapy water instead. The safe default is the lowest setting that works, with cleaner doing the lifting.
The one thing every brand agrees on is drainage. Keep the gaps between boards clear, keep planters and mats from trapping water, and the deck will need washing far less often. For the patio around the deck, see what PSI pavers take, and for the chairs that sit on it, patio furniture.
Which pressure washers suit composite decking?
Mid-range electric machines with adjustable pressure. Bigger is not better on a capped board. Tiered options are in the best pressure washers.
Kärcher K 5 Premium Electric Pressure Washer with Hose Reel
$386.01Vario Power adjusts pressure at the wand, which makes it easy to stay under a decking maker's published limit, and the hose reel keeps 25 feet of hose off the boards.
Best for: capped composite and PVC decking
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Greenworks 2000 PSI 1.2 GPM Electric Pressure Washer
$194.99PWMA-rated 2,000 PSI and 1.2 GPM with auto stop, so the pump is not running while you reposition furniture, and an onboard soap tank for composite cleaner.
Best for: mid-size decks cleaned once or twice a year
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Westinghouse ePX3500 Electric Pressure Washer
$169.00A 19 pound anti-tip body with a 25 foot braided hose, rated 2,000 PSI and 1.2 GPM. Light enough to carry up deck stairs and set down without marking boards.
Best for: raised decks and second story balconies
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Sun Joe SPX3000 Electric Pressure Washer
$169.00Two detergent tanks and five tips including 40 degree and soap. Keeping the deck cleaner loaded means you use chemistry instead of reaching for a narrower tip.
Best for: small decks and first-time buyers
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We did not test these products in person. Picks are researched from manufacturer specifications and owner manuals, engine and safety certifications where they apply, warranty terms, public recall records, and the recurring themes in verified owner reviews. We favor established brands with large review counts and parts support, match each pick to a real yard size or task, and place it in the tier where its price and capability actually belong.
Frequently asked questions
Can you pressure wash Trex or other composite decking?
Often yes, at low pressure, but the decking maker decides. Several composite and PVC brands publish a maximum pressure and nozzle distance, and some warn that pressure washing can affect the warranty. The general range for composite is 1,000 to 1,500 PSI with a 40 degree fan held 8 to 12 inches away. Check your brand first and use their cleaner if they name one.
What is the black speckling on my composite deck?
Usually mold or mildew growing in organic film on the surface, which is why it appears worst in shade and where leaves collect. Pressure does not solve it on its own. Clear the gaps between boards so water drains, apply a composite-safe cleaner and let it dwell, then rinse with a wide fan. Keeping debris out of the gaps prevents most of it coming back.
Is composite decking easier to clean than wood?
Generally yes. Composite does not gouge or fuzz the way soft pine does, so a wider safe pressure range applies, 1,000 to 1,500 PSI against 500 to 1,200 for wood. The trade-off is that damage to the capped surface cannot be sanded out. With wood you can sand and re-stain; with composite a dull streak stays.
Researched, not professional advice. This page is compiled from published specifications, manuals, labels and owner-review consensus, not hands-on testing. Follow the manufacturer's instructions and product label, and consult a qualified professional where safety, chemicals, fuel or structures are involved. As an Amazon Associate we earn from qualifying purchases.