Eastern white cedar (Thuja occidentalis L.) is a naturally durable wood species due to toxic compounds present in the heartwood. These compounds may serve as natural fungicides to protect nondurable wood products from biodegradation. This study was intended to improve the effectiveness of posttreating aspen oriented strand board (OSB) panels with white cedar heartwood extracts against mold and decay by co-applying a protective coating. The results showed that aspen OSB samples treated with the white cedar water-soluble heartwood extracts had little mold infection. No mold growth was detected on any samples that were dip treated with the extracts and then brushed with a coating. The decay test showed that most samples treated with both white cedar heartwood extracts and a coating had significantly less weight loss than untreated control samples. Using coating products alone also reduced mold and decay growth on OSB samples; however, adding cedar extracts to the treatment significantly improved the performance of one of the three coating products tested against mold and decay.