Composite decking is one of the most popular decking materials, and with good reason—it's durable, attractive and inexpensive. But even the most ardent fan of this type of deck won't be a fan of cleaning composite decks. That said, if you follow the recommended instructions for cleaning your composite deck, you can expect it to stay looking great for years.
It's generally suggested that you use a power washer to clean a composite deck. Be sure to check with your deck's manufacturer or installer to determine the recommended tip to and pressure setting to use.
Once you've swept all debris from your deck, you're ready to power wash. Be sure to start washing in a place that you wouldn't have too much trouble replacing—a smaller board or a step, perhaps—in case your setting is off for some reason. Better to damage a small portion of the wood in a less prominent location than a centrally located, larger piece.
Once power washing is done, you'll want to apply a degreaser/stain remover, or a professional grade deck cleaning solution. Be sure to follow the manufacturer's instructions for mixing. One other factor to consider is that it's often recommended that you apply the cleaner in the early morning or evening hours so that the cleaner doesn't evaporate in the sun.
Once the cleaner has been on the boards for the period the manufacturer recommends, spray the deck clean with the power washer. You should then allow at least 24 hours before applying any further treatments or stains to the deck, in order to ensure that it's completely dry.