Water Soak Versus Wicking Test for Hardboard Siding

Occasional hardboard siding failures, as the result of biological deterioration, are a major concern to siding manufacturers. These failures have occurred in material which had passed the industry water absorption and thickness swelling specifications with the ASTM 24-hour water soak test. An exploratory study was conducted with hardboard siding to evaluate the applicability of the 24-hour water soak test to this product. The penetration of water into siding samples was determined by cutting successive perimeter strips from the edges of the 24-hour submersion sample and determining the moisture content of each perimeter strip. These results were compared to the moisture content of successive edge strips removed from a wicking specimen of the same siding suspended vertically so that only one edge was submerged in water. The 24-hour submersion test resulted in similar penetration for all samples tested but significant differences between samples were noted with the edge wicking test. Siding which had failed in service had a much larger quantity of water wicking into the sample than was found for the more recently produced material. Water wicked more than 6 inches above the waterline in one of the failed samples. A hypothesis is presented that entrapped air is responsible for the limited penetration inherent in the 24-hour water soak test.

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