Mold on Trex Deck - Knowledgebase Question

commerce twp., Mi
Question by jackiekbowen
April 14, 2010
I had a trex deck installed several years ago. It has mold all over it. I cleaned it last year with a bleach solution, but it came right back. What can I do?

Answer from NGA
April 14, 2010


Mold is a lower form of plant life that can settle and grow on any surface, including Trex? decking. Mildew is a form of mold that grows on damp surfaces.

Mold spores are similar to seeds, but cannot be seen until colonies form. Air currents, insects, animals and water transport the spores easily. Due to mold?s adaptability and large number of species, it is very hard to control and impossible to totally eliminate. Mold will not affect the structural performance of Trex decking.

In order to form visible colonies, mold needs food, moisture, and temperatures between 40 and 90? F. Trex decking is not a food source for mold, but can collect food in the form of dirt and debris such as the overflow from flowerpots and gutters. Trex decking can also supply moisture if the gaps between deck boards are too small or clogged.

All exterior building materials require cleaning and Trex is no exception. Periodic cleaning of Trex decking will remove dirt and pollen that can feed mold. If mold colonies appear, clean the deck with a commercial deck wash containing a detergent and sodium hypochlorite, commonly known as bleach. This chemical will remove the mold, but be aware it will also lighten the wood on the surface. In some cases it will require several treatments with the deck wash to completely remove all mold colonies. Even if the spots are no longer visible, there may still be mold spores on the surface that could re-grow, so periodic cleaning is important.

The following brands of deck cleaners have been found to be effective in removing mold from Trex decking: Olympic Deck Wash; Expert Chemical?** Composite Deck Cleaner & Enhancer.

You may need to clean your deck every spring to keep mold from growing. Best wishes with your deck.

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