Zinc borate (ZB) is being used as an antifungal and insecticidal wood preservative for flake/strand-based composites. Data is reported on the laboratory and field leaching behavior of ZB when contained in apen flake composites. In general, the performance results correlate with leaching hazard. Although the boron in ZB is more resistant to depletion than in sodium borates, the ZB boron will deplete over time under severe leaching conditions. In climates and/or exposures with higher leaching hazard, more depletion and corresponding fungal/insect attack is observed. The zinc component of ZB is much more resistant to depletion, but does not contribute as much to the preservative efficacy. Some depletion data indicates that a "reservoir" effect can occur, where boron from regions with a high ZB loading diffuses into regions of the test specimen with low loadings due to depletion. The good level of performance under these test conditions continues to support the use of ZB in protected exterior wood composite applications.

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