Here are the dos and don'ts of to keep your composite deck looking great.
Tools and Techniques for Cleaning Composite Decking
Composite decking is durable and low-maintenance. But low maintenance doesn’t mean zero maintenance. You still have to clean it to keep it looking its best.
This is a struggle I know first-hand. I’m lucky enough to have two big, beautiful oak trees near our home. But that also means that every year, our composite decking is coated with oak pollen. And every year, I have to scrub that pollen off.
Whether you’re struggling with pollen, falling leaves, dirty shoe prints, or simply want your deck to look great, the good news is that deck cleaning is straightforward and makes for a great DIY project. I reached out to a deck cleaning pro and consulted composite decking manufacturers to get the low-down on the best tools and techniques to extend the life and beauty of a composite deck.
Cleaning a composite deck requires three things: water, agitation, and a cleaning chemical. How much of each and what type you use will depend on the type of deck and what you’re cleaning off of it.
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Composite Deck Cleaning Chemicals
“The key to cleaning a composite deck is the cleaner itself,” says Scott Paul, owner of DeckStainHelp.com. In his view, the cleaner should do the bulk of the work, separating dirt from the deck surface so you can easily wash it away.
The trick to selecting the right cleaner is avoiding anything that might discolor the deck. Start with the least aggressive solution, such as dish soap. If the dirt or stains persist, then move up to a dedicated deck cleaner.
At this point, Paul advises checking the ingredients of any potential deck-cleaning chemical. “Avoid using bleach or any deck cleaners using bleach unless necessary,” he says. Instead, Paul recommends looking for a cleaner that lists sodium percarbonate as a key ingredient. This makes for a more gentle treatment than a bleach-based cleaner. (Watch for the ingredient “sodium hypochlorite” — that’s full-on bleach, the same stuff that’ll ruin your jeans if you put too much in the wash.)
Composite decking made in the last five to ten years is almost entirely plastic, making it particularly susceptible to aggressive cleaners. Scott Paul advises against using any bleach-based deck cleaners on these newer decks.
Older composite decking has their vulnerabilities as well. Because of their lower plastic-to-wood ratio, says Paul. “These older composites are very porous and are prone to UV discoloration and mildew/mold issues.” If the mildew has gotten deep into the composite decking, it may require a bleach treatment. “In these cases,” says Paul, “we suggest mixing a solution of 1 part bleach to 4 parts water. Apply to the composite decking with a pump sprayer and lightly pressure wash off after 10–20 minutes.”
When in doubt, always test the cleaner on an out-of-the-way section of the deck first, to see how it reacts.
Composite Deck Agitation
In an ideal world, you could simply apply a cleaner and then wipe away any dirt by spraying the deck with a garden hose. In reality, you’ll need at least some level of scrubbing, so have a soft-bristle nylon brush close by.
I reached out to composite deck manufacturer Trex, and spokesperson Leslie Adkins provided extensive resources on how to care for their specific lines. One of the most striking elements is how the appropriate level of agitation can depend on the specific decking line.
For example, early-generation Trex composite products should never be cleaned with a pressure washer, as doing so can damage the material and void the warranty. But newer lines can be pressure washed, as long as the pressure isn’t too high.
We’ll discuss pressure washing in more depth later. For now, remember that you can start with gentle spraying and then move on to scrubbing as needed.
Water
Using water to clean a deck may seem self-evident, but if you have very hard water, it can leave mineral residue on the decking after you clean. If that happens to you, wipe the decking down with white vinegar, then rinse again with soft water.
Composite Deck Cleaning Challenges
Food and Grease
Clean these spills ASAP! Grease can react with the plastics in composite decking. When caught quickly the clean-up doesn’t take much effort – simply treat the spill with warm, soapy water and spray clean with a hose.
General Dirt
The most common type of deck mess is also the easiest to clean. Light dirt and soiling can typically be removed with soapy water and a garden hose.
Leaf Residue and Tannins
Leaves are easy enough to sweep away, but if allowed to sit for too long they can leave a tannin residue, staining the surface of composite decking. Trex recommends using a deck “brightener” to the deck as directed by the manufacturer. Apply some on an inconspicuous area first to see if you like the look.
Pollen
The experts at Trex told me that pollen can feed mold, making it even more important to keep it off composite decks. They advise, “To remove pollen, sweep the deck clear and then scrub the surface with warm soapy water and a soft bristle brush. You can also try power washing with a 1500 PSI pressure washer.”
Can you Pressure Wash a Composite Deck?
“Yes,” says Paul, “you can pressure wash after using a proper deck cleaner and at a very low pressure.” He recommends washing at no higher than 1200 PSI (pounds per square inch), and stresses that you should keep the pressure washer tip at least eight to twelve inches from the decking.
Manufacturers often give for specific product lines. For example, TimberTech suggests a maximum 1500 PSI, while Trex recommends 1500 PSI for basic cleaning and up to 3100 PSI max for serious cleaning on newer lines like Transcend. But for their older lines, Trex advises no pressure washing at all.
Regular Maintenance
One of the great things about composite decking is that there’s not much maintenance required.
Composite decking manufacturer Trex recommends maintenance cleaning in the spring (to get ready for outdoor living) and in the winter, shortly before the first snowfall.
Speaking of snow, both Trex and TimberTech strongly recommend against using a metal or metal-edge snow shovel to clear your deck. It’s too easy to scratch the deck surface.
Sealing a Composite Deck
Many readers wonder if they need to reseal their composite decks like a wooden deck.
While newer composite decks don’t ever need to be sealed (and, in fact, can’t be stained or sealed) Paul says there may be an option to seal decks that are over ten years old.
“The older, porous composites can be sealed with a clear deck coating or even a penetrating semi-transparent deck stain,” he says. “This will help prevent mold/mildew and with the penetrating semi-transparent deck stains, it can help restore the appearance if UV faded from the sun damage.”
FAQs
Besides cleaning, what other maintenance does composite decking require?
Very little! Clean any spills as soon as possible, especially if they involve grease or oils. Both Trex and TimberTech caution against leaving oil-based items (like welcome mats with a rubber backing) directly on the decking, as they can discolor the surface.
Is composite decking easier to clean than wood?
“Cleaning composite decks is very similar to cleaning wood decks,” says Paul. The basic steps and tools are largely the same.
About the Expert
Scott Paul has been cleaning and restoring decks since 1993. Today he is the owner of DeckStainHelp.com, and is an authority in the deck restoration industry, contributing to numerous wood restoration forums and informative sites. Scott and his companies have restored over 10,000 decks in the Metro Detroit area.
Sources
Leslie Adkins is the Group Vice President of Marketing and ESG Development at Trex Company. Via electronic interview.
