Biocides and Mold Resistance

Some WPC materials contain biocides to inhibit microbial growth, while others do not. However, it is not always easy to tell whether those biocides in chosen amounts in the given composite material are actually effective. 

Biocides are often called—depending on their assumed application—as fungicides, mildewcides, antibacterials, or preservatives. Biocides essentially suppress the growth of different microorganisms, but in a different extent, depending on mechanisms of action of biocides and life features of microorganisms. 

The whole area of mold resistance in composite materials is rather ill-defined. Typically, it is not clear, what resistance is under consideration resistance to microbial degradation of the composite material (weight loss, loss of the integrity of the material) or resistance to mold growing at the surface, without penetration into the matrix, without violation of the structural integrity of the material. 

In other words, microbial degradation of WPC means deterioration of the material, while mold growing at the surface does not mean actual deterioration but brings about a merely visual factor, though aesthetically repulsive. The composite material in the last case is still intact, as well as the original material. A plain pressure-washing would remove mold from the surface of a composite material. 

There is a wide variety of biocides recommended (by manufacturers) for application in WPCs. Some of those biocides are totally ineffective in the real world some are effective but only toward certain microbial species, not necessarily troublemakers for the particular composite in a given geographical region. Some of them will leach out of the composite rather soon. Some of them, on the contrary. 

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