Linda Meyer

Critical moisture conditions for fungal decay of modified wood by basidiomycetes as detected by pile tests

Abstract The aim of cell wall modification is to keep wood moisture content (MC) below favorable conditions for decay organisms. However, thermally modified, furfurylated, and acetylated woods partly show higher MCs than untreated wood in outdoor exposure. The open question is to which extent decay is influenced by the presence of liquid water in cell lumens. The present paper contributes to this topic and reports on physiological threshold values for wood decay fungi with respect to modified wood. In total, 4200 specimens made from acetylated, furfurylated, and thermally modified beech wood (Fagus sylvatica L.) and Scots pine sapwood (sW) (Pinus sylvestris L.) were exposed to Coniophora puteana and Trametes versicolor. Piles consisting of 50 small specimens were incubated above malt agar in Erlenmeyer flasks for 16 weeks. In general, pile upward mass loss (ML) and MC decreased. Threshold values for fungal growth and decay (ML≥2%) were determined. In summary, the minimum MC for fungal decay was slightly below fiber saturation point of the majority of the untreated and differently modified materials. Surprisingly, T. versicolor was able to degrade untreated beech wood at a minimum of 15% MC, and growth was possible at 13% MC. By contrast, untreated pine sW was not decayed by C. puteana at less than 29% MC.

The potential of moisture content measurements for testing the durability of timber products

Traditionally, the durability of timber is determined in laboratory decay tests or ground contact field tests. Since it is commonly accepted that results from those tests are not directly transferable to less severe above-ground exposures, this study aimed at assessing alternative durability measures related to the moisture performance of wood. Results from above-ground tests including continuous wood moisture monitoring were analyzed. Decay ratings determined in double-layer field tests were compared with time of wetness, and temperature- and moisture-induced dose according to a dose–response model for above-ground decay. Significant differences between European wood species were found in façade, decking, sandwich, lap-joint, and double-layer tests with respect to their moisture performance. It is concluded that for many wood-based products intended for above-ground use, a combination of short-term laboratory decay tests and mid-term moisture performance field tests may serve as time-saving alternative to long-term decay tests in the field.

Testing the durability of timber above ground: A review on methodology

Abstract The majority of timber products in outdoor use are exposed above ground, e.g. façades, terrace decking, playground equipment, garden furniture, windows, balconies or carports. In contrast, the durability of wood and wood products is most often determined in laboratory against Basidiomycete monocultures or in-ground field tests, where wood samples are submitted to permanent wetting. Worldwide, only a few above ground field test methods evaluating durability against fungal decay have been standardized. Wood used in above ground situations can be exposed to a wide range of moisture loads reflecting different design details such as varying shelter, distance to ground, ventilation and water trapping, whereas temperature and rainfall variations are overall influences on service life performance. The aim of this review was to gather information about standardized and non-standardized above ground field test methods used to determine the durability of wood and wood-based products. In total, more than 60 methods have been evaluated according to different criteria, such as principle set-up and design, severity of exposure and distance to ground. Their suitability to reflect a certain exposure under real-life conditions is discussed as well as practical aspects regarding acceleration measures, decay assessment and practicability, costs and time efforts.

Dynamic and static hardness of wood: method development and comparative studies

Abstract Hardness is considered to be one of the most important surface properties of flooring materials. Numerous methods for hardness testing exist; they vary in terms of load application as well as shape and type of the indenting body. For wood-based materials Brinell hardness tests are used most commonly. Based on the Brinell hardness principle, this study focused on developing a method to determine the dynamic hardness of wooden materials. It aimed to examine differences between static and dynamic loads on hardness as well as the possibility to convert both hardness values into each other. Extensive hardness tests with 24 different native wood species and thermally modified timber were conducted. The method for dynamic hardness testing was found to be easily and reliably applicable on various kinds of wood-based materials. Compared with standard static methods, it is less time and cost consuming and allowed mobility.

Intrasite variability of fungal decay on wood exposed in ground contact

Abstract Timber exposed in the ground faces most severe conditions in terms of exposure to wetting and fungal decay in the terrestrial environment, therefore wood durability tests are often conducted in test fields preferably ensuring the occurrence of all relevant decay organisms. One can also expect differences in decay within an individual field test site due to localised distribution of certain organisms. Therefore, relevant decay parameters were examined on the newly prepared in-ground test field in Herrenhausen, Hannover: Scots pine sapwood and European beech were exposed to record distribution of decay types, decay intensity and soil parameters. Soft and white rot were found to be dominating. Significant differences of the intrasite variability of decay intensity were observed between wood species and over time. In contrast, differences in decay intensity by different rot types were small. It was concluded that spatial differences in decay intensity were due to localised established fungal flora.

Testing the mechanical resistance of timber used for construction in the marine environment

Abstract The paper describes refinements of rapid laboratory assessment of the mechanical performance of timbers used in the marine environment as regards their resistance to indentation, impact abrasion from smooth and sharp abrasives and to dynamic impact loads when wet. Ten tropical and home-grown hardwoods, five softwoods and a wood–polymer compound were examined. Brinell hardness, dynamic hardness, abrasion resistance, and the structural integrity in high-energy multiple impact tests were determined comparatively on dry and wet specimens. A trend was shown where softwoods show a decrease in abrasion resistance with wetting, whilst hardwoods did not. In dry conditions, impact abrasion using steel balls was higher than when using sharp grit. It is suggested that when wet, water in the cells has a hydraulic energy absorbing effect.

Natural durability of timber exposed above ground - A survey [Prirodna trajnost drva izlozenoga iznad zemlje - Pregled istrazivanja]

Besides its inherent resistance against degrading organisms, the durability of timber is infl uenced by design details and climatic conditions, making it diffi cult to treat wood durability as an absolute value. Durability classifi cation is, therefore, based on comparing performance indicators between the timber in question and a reference timber. These relative values are grouped and related to durability classes, which can refer to a high range of service-lives. The insuffi cient comparability of such durability records has turned out to be a key challenge for service-life prediction. This paper reviewed literature data, based on service-life measures, not masked by a durability classifi cation. It focused on natural durability of timber tested in the fi eld above-ground. Additionally, results from ongoing aboveground durability studies in Europe and Australia are presented and have been used for further analysis. In total, 163 durability recordings from 31 different test sites worldwide based on ten different test methods have been considered for calculation of resistance factors. The datasets were heterogeneous in quality and quantity; the resulting resistance factors suffered from high variation. In conclusion, an open platform for scientifi c exchange is needed to increase the amount of available service-life related data.