Influence of Artificial and Natural Weathering on the Moisture Dynamic of Wood

Abstract

Wood that is used in outdoor applications is frequently exposed to weathering and is thus prone to fungal degradation. Ways to prevent fungal degradation include keeping the wood dry. The majority of hydrophobic and wood modification systems have been tested only on freshly treated wood. Little information is available on how various woodbased materials perform after a certain period of weathering. To elucidate this question, 17 wood samples were tested from the following species: oak (Quercus), sweet chestnut (Castanea sativa), European larch (Larix decidua), Scots pine heartwood and sapwood (Pinus sylvestris), Norway spruce (Picea abies), and beech (Fagus sylvatica). Moisture performance of the wood samples was improved with thermal modification, wax, oil, and biocide treatment. Specimens were exposed to various degradation-aging factors (blue stain fungi, decay fungi, artificial weathering, and natural weathering). Various moisture performance tests were applied before and after aging: short-term water uptake (tensiometer), long-term water uptake, water vapor tests, drying tests, etc. The water exclusion efficacy of wood was decreased after aging. Aging factors were found to act synergistically and to have a more prominent influence on less durable wood compared to durable or preservative-treated wood. Wax-treated wood performed best, regardless of which moisture performance test was applied.

Moisture behavior of weathered wood surfaces during cyclic wetting: measurements and modeling

“…The results of the present study show the effects of weathering to be most pronounced at the surface, which is in agreement with the results by Žlahtič and Humar (2016) where it was shown that mainly the short-term water uptake increased due to weathering. In one-dimensional capillary absorption, such as in the floating test, the moisture uptake of porous materials is generally found to be proportional to the square root of the time, t 1/2 .…”

“…Most of the photodegradation and checking occurs within weeks of exposure, but can continue for at least 6-12 months before developing to continuous slow erosion (Evans 2013;Evans et al 2008;Kalnins and Feist 1993). Žlahtič and Humar (2016) recently found a difference in moisture absorption between specimens that had been subjected to outdoor weathering for 9 months and for 18 months, respectively. However, these tests did not exclude the occurrence of effects stemming from staining fungi.…”

“…Similar long-term trends have been observed in other publications where they were attributed to cracks, surface checks, staining fungi or weathering in general (Brischke and Melcher 2015;Meyer et al 2015). Although it has been widely established that such effects increase the volume of water absorbed during wetting (Žlahtič and Humar 2016), it is not clear how the depth and nature of the damaged surface layer affect the liquid moisture uptake, the accumulation of moisture in the wood core and consequently the risk of the moisture content exceeding critical thresholds in the overall cross section of the element with respect to decay.…”

The Performance of Wood Decking after Five Years of Exposure: Verification of the Combined Effect of Wetting Ability and Durability

“…We assume that the decreased moisture performance may be associated with fungal decay. Fungi open up new voids in the cell matrix, which results in better permeability [48]. One possible explanation for increased electrical conductivity (hence, increased MC) could be the consequence of fungal colonisation, due to the presence of electrolytes excreted by the fungi.…”

Assessment of efficacy and effectiveness of some extracted bio-chemicals as bio-fungicides on wood

“…Furthermore, the elemental composition of some wood species, Pinus rigida, Juglans nigra, and Fagus sylvatica, Citharexylum spinosum and Morus alba, changed after inoculation with Penicillium selerotigenum, Paecilomyces variotii, and Aspergillus niger (Mansour et al, 2015a;Salem, 2016). Other studies reported that the aging factors act synergistically to have a more prominent infl uence on less durable-wood compared to durable or preservativetreated wood (Žlahtič and Humar, 2017). Also, there is a strong correlation between the moisture content of the cell wall and the ability of microorganisms to degrade wood (Schmidt, 2006;Van Meel et al, 2011; Meyer and Brischke, 2015).…”