Mold. The word can cause panic among wood users and especially among pallet manufacturers whose customers often demand mold-free wood. 

BY JEFF MORRELL, PH.D.

Mold means different things to different wood users. There are literally thousands of fungi that can land on a wood surface and grow. Some of these fungi degrade the structural polymers that give wood its unique properties. Others only use sugars, proteins or other compounds stored within the wood, and others still may just be growing on material on the wood surface (such as dust or pollen). Some are not visible to the naked eye, while others markedly discolor the wood.

For the purposes of this short review, we will consider molds to be those fungi that produce pigmented spores on the wood surface. These spores are typically capable of becoming airborne and can land on any wet wood where they germinate to produce hyphae that grow into the wood to use stored sugars, proteins and other compounds. Once the fungus obtains enough energy, it produces spores on the wood surface to start the cycle again on another piece of wood. This process can take a few days but can also extend to months or years, depending on the fungus and the environmental conditions.

Wood species can also affect the risk of mold. Species with more sapwood or more stored sugars are at a higher risk of fungal attack. Mold spores can usually be brushed from the wood surface, leaving little evidence of their presence; however, the fungus is still very much alive in the wood and can continue to grow and produce new spores if the wood remains wet.

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