An experimental set-up for real-time continuous moisture measurements of plywood exposed to outdoor climate

Plywood used in exterior conditions is prone to water uptake and release. The influence of moisture on the strength properties and the decay risk is substantial. Therefore it is crucial to gather knowledge on the moisture behaviour of plywood in service, especially considering the fact that the intrinsic durability of the wood species used, is not exclusively determining outdoor performance. An automatic measurement set-up is proposed. The concept relies on a logger system recording the weight of plywood samples mounted on calibrated load cells. Mass changes are attributed to changes in moisture content induced by monitored environmental conditions such as solar irradiation, wind, rain and relative humidity. Pre- and post-processing of 10 plywood types is elaborated on. Logically, the length of a rain event has an influence on the moisture content of plywood. Differences in moisture dynamics of different plywood types are attributed to veneer thickness, glue type and wood species and their susceptibility to weathering. Further straightforward correlation was found between plywood moisture content, temperature and relative humidity. Time of wetness calculation based on these data illustrates the moisture dynamics of plywood and is a potential basis for service life prediction of plywood. (C) 2009 Elsevier Ltd. All rights reserved.