Cleaning composite decking material is an increasing service being requested due to mold growth which starts in the pours and over time resembles black quarter size spots usually clumped in certain areas of the deck. What I have found to work quite well as a cleaner is oxyout mold cleaner. Follow the directions on the package for best results. Next, powerwash the deck similar as you would any other decking material. Do not attemt to use a powerwasher if you dont have enough experience as the damage you may cause is not reversable. A medium bristle brush and some elbow grease will due just fine, rinse when complete. Let the deck dry for 48 hours and apply either oxyshield mold and algae barrier to prevent the onset of new mold growth, or if you just want to fill the pours and have water and other liquids bead off, a good protectant to seal the deck would be a siloxane type sealer such as superseal m. Neither product will change the appearance of the deck when dry. If your deck is fairly new and all of the boards do not match, dont worry, as with any decking material over time they all fade together.

Chris-

Have you tried using any of the Composite Wood Stains? These are helpful for the 10 year old Trex decks that have lost all of their color.

Yes I have, they are good too, I like to stick with similar colors though, I havent tried to switch colors yet. Still these products are newer to the market and I anticipate they will get better in time.

If you have any pictures of your work please post them in the Scrapbook section.

Another cleaner that I have tried and worked well is one half cup of household bleach, per gallon of water. If this process may make you nervous for some reason, just try an area which is out of site [like the underside of the deck], it kills the mold on contact, allowing it to be lifted off with a light wash.

Can you please explain a few things so we have a better understanding of why certain procedures need to be taken. For instance "If you do not have experience with a powerwasher, and as you suggest it can damage the deck. Would the only option be to pay someone to do it? and if so how can you be sure you are getting someone with experience?"

Ask for references, call the bbb, look at some of their local work, good guys usually wont ask for payment up front, unless it is a very large job, ask neighbors, friends, look them in the eye, just to name a few. Get a few bids [like 3] and go from there.