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

Abstract

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 outdoorperformance. 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.

Combining electrical resistance and 3-D X-ray computed tomography for moisture distribution measurements in wood products exposed in dynamic moisture conditions

“…To continuously record the MC distribution using the electrical method under inservice conditions, a combination with other measurement methods is most useful. For example, CMM (continuous moisture measurement) and a weather station can be used to record the average MC of the specimens and all possible weather information [3]. As such the data recorded by the electrical method can be further optimized e.g.…”

“…[3]). Contrary to solid wood, the glue lines separate the veneers and hamper water movement between them.…”

“…), all measuring 70 x 50 x 15 mm 3 and 50 mm along the grain direction. Also PF (phenol formaldehyde) glued plywood, and OSB panels with isocyanate glue, were prepared and sawn to the size of 70 x 50 x panel thickness mm 3 (Table 1). All specimens were without decay, knots and obvious defects.…”

“…Hence it is crucial to monitor MC when wood is used outdoors to better understand its behaviour when subjected to dynamic outdoor conditions with possible liquid water ingress. Previous study by Van den Bulcke and co-workers [3] introduced the CMM method, with continuously weighing of plywood exposed outdoors for calculation of the average MC of the samples. Moisture distribution is a key factor as well.…”

Moisture behavior and structural changes of plywood during outdoor exposure

“…Knowledge on moisture behavior is thus essential to protect plywood panels and predict their changing properties in service. To obtain the average moisture content (MC) of wood samples and from wood derived materials, a continuous moisture measurement (CMM) set-up was developed, which can continuously weigh specimens' mass and simultaneously record the local climate (Van den Bulcke et al 2009). Based on the data from this CMM setup, the relation between weather data and the amount of days with an average MC higher than 20% or 25% was further analyzed (Van den .…”