How to Minimize and Prevent Mold Growth on Decks

Just like wood, uncapped composite decking can develop mold. Learn how and why this can happen, what to do to remove it, and the steps you can take to prevent mold from returning.

Mold is a natural environmental occurrence. If the conditions are right, it can show up almost anywhere – on wood, vinyl, sheetrock, or even decking. It’s not a product defect, so it’s rarely, if ever, covered under most product performance warranties.

Mold can occur on almost any material, including wood decking and uncapped composite decking. 

There are steps you can take to minimize the likelihood of mold growth. Mold is much more pervasive on wood and uncapped decking products, so choosing a capped composite deck board is a smart first step.  “Cap” is a common industry term used to describe the protective outer layer that surrounds the wood-plastic core of the deck board. At Fiberon, our patented cap layer is called PermaTech®, and it contains a special formulation of biocides, anti-oxidants, and other proprietary ingredients. This unique blend of ingredients helps the composite decking resist staining and fading, as well as inhibits mold growth. And while no one can guarantee a deck will never develop mold, a capped composite board does provide significant advantages over wood and uncapped products.

What causes mold?

Most often, mold results from airborne pollen, fertilizer overspray, or leaf litter (although not exclusively). Mold spores are lightweight and become airborne easily. If they are in the surrounding environment -- the eaves of a home, the roof, or a fence, for example -- they can settle onto the decking. Once there, it takes only a few key ingredients for the mold to grow.

 How does mold grow on decking?

To thrive, mold and mildew need four things: air, water, 40°-100° temperatures, and a food source. Leaves, debris, pollen, and other organic materials are an excellent food source for mold development, so it pays to keep your deck clean. Even so, there is no way to completely eliminate all of these environmental conditions.

The porous nature of decking aids the process, as mold spores will settle into these pores and root. Once moisture, heat, and a food supply are introduced, the spores will bloom and create dark spots on the boards. Eventually this will spread across the deck. If the boards are not thoroughly cleaned of mold and its rooting, the mold will return -- especially if it is prevalent in the environment around the deck.

Clean your deck regularly to minimize mold

Fiberon Horizon Composite Decking (shown in Ipe with Tudor Brown accents) features a four-sided PermaTech cap layer for added protection against staining and fading, as well as superior mold resistance. 

To minimize mold on the decking, clean the deck as often as needed but at least twice each year. Climate conditions vary in different regions of the country and may necessitate more periodic cleaning. In some situations, you may need to repeat the cleaning process multiple times until you are no longer able to see any “shadows” of the spots on your deck while it is wet. You would also want to apply a mold inhibitor to retard future growth. Once the decking has been thoroughly cleaned, you will need to maintain it in much the same way you would adhere to a cleaning schedule for any other significant item in or around your home.


Should a deck with mold be power-washed?

No. Power-washing will only worsen the mold problem. The pressure of the power washer actually pushes the mold further down into the pores of the material. We DO NOT recommend power washing the decking while mold or mildew is present.  If a pressure washer has been used, we recommend at least two applications of cleaner to ensure that the roots of the mold are thoroughly neutralized. A pressure washer can also, if used improperly, damage the deck surface. We recommend exercising extreme caution when using a pressure washer for deck cleaning. Remember to keep the tip at least 12 inches from the deck surface to prevent damage.

Power-washing mold from a deck doesn’t work. You’ll only exacerbate the problem.

What products are recommended for removing mold from a deck?

Fiberon recommends the following two products:

•  30 Seconds® Outdoor Cleaner
•  30 Seconds® Spray and Walk Away

When used in combination, these two products provide a “one-two” punch to help control mold and mildew. Both are heavy duty, mildly alkaline, chlorinated mold and mildew removers/cleaners that are biodegradable once rinsed into the soil. Both have been tested and perform very well in removing mold and mildew and retarding its return on our uncapped composite decking. Consumers can find these products on the manufacturer’s website, at most Home Depot® locations, and through They are also available at most Walmart® stores and Ace® Hardware locations.

30 Seconds® Outdoor Cleaner works on composites, as well as wood, vinyl, concrete, brick, stucco, and outdoor fabrics. Homeowners may choose to use this on other outdoor materials that are exhibiting mold/mildew/algae growth, such as deck furniture, siding, or gutters.

An annual (or bi-annual) thorough cleaning is a smart way to minimize the chance of mold. Shown here: Fiberon Symmetry Composite Decking in Warm Sienna with Symmetry Railing in Tranquil White.

When using this cleaner, be aware that the porous nature of uncapped decking demands a minimum of 5-10 minutes of wetting time, not "30 seconds" as the product name suggests.
Once the deck is thoroughly cleaned and dry, we recommend applying an inhibitor such as the 30 Seconds® Spray and Walk Away. This product is activated when it gets wet (i.e. when it rains) and helps to keep the mold growth at bay for longer periods of time; therefore, fewer cleanings are required. You would only apply this product when needed, but no more than six times per year. Even so, we do recommend Fiberon composite deck owners clean their decking with an approved cleaner at least twice a year. For more composite deck cleaning tips, download the Care and Maintenance Guide.


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