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Sunday, 22 January 2017

Wood Rot Protection

Protection focuses on fundamentals upon prevention of wood damage by fungi, and protection and preservation of wood (e.g., Willeitner and Liese 1992; Eaton and Hale 1993; Palfreyman et al. 1996; Murphy and Dickinson 1997; Zujest 2003; Goodell et al. 2003; Muller 2005). 

Protection in the broader sense comprises non-chemical methods like organizational measures and measures by design, use of naturally durable woods, application of antagonisms, or wood modifications that do not affect the environment. Preservation predominantly stands for chemical measures.  

The conditions for the development of wood fungi and protection principles that can be deduced from them. The principle of the wood protection consists of changing at least one of the three life prerequisites of fungi in wood in such a way that the development of fungi is impossible or at least inhibited. Fungal attack can be prevented  (Willeitner and Schwab 1981; Erler 2002; Willeitner 2000, 2003; Goodell et al. 2003; BOttcher 2005; Borsch-Laaks 2005; Schmidt 2005) by: - organizational protection (e.g., short and appropriate wood storage), - use of durable wood species (natural methods), - keeping away water by structural wood protection measures by design: appropriate surface and weather protection, use of vapor barriers, avoidance of condensation due to thermal insulations, salient roof to protect timber from rain, drawing off of rain, barrier to avoid direct contact between wood and adjacent material, or inside the wall against raise of moisture from the ground, - chemical wood preservation, - wood modifications that increase dimensional stability of wood, reduce uptake of moisture, or make it hard to digest, - use of antagonisms. 

The moisture conditions in wood are of decisive importance for the develop-ment of wood fungi . The hazard classes of wood [to be replaced by "use classes" according to prEN 335-1 (2004) respectively ISO] that depend on wood use and timber moisture according to the German standard DIN 68800, parts 2 and 3 (1990, 1996), the corresponding potential application of durable timber, and the minimum requirements of chemical preservation measures. 

Natural durability means the wood-own resistance against bacteria, wood-decay fungi, beetles, termites and marine borers, which will differ for a timber species against the various organisms. Wood durability is based on the pres-ence of accessory compounds, whereby it concerns numerous compounds from different chemical classes (Fengel and Wegener 1989; Obst 1998). They are pro-duced in the living tree during transition from the sapwood to the heartwood and are deposited in the heartwood (Taylor et al. 2002). 

Thus only the heart-wood exhibits natural durability, while the sapwood of all wood species is only little or not durable. The European standard EN 350-2 (1994) uses a five-class system to group 128 timbers according to their durability against fungi. Wood with high durability against fungi (durability class 1, very durable) is e.g., greenheart (durable also against termites and marine organisms). 

European oak is durable (class 2), walnut is moderately durable (class 3), Norway spruce is slightly durable (class 4), and European beech not durable (class 5) (also Au-gusta and Rapp 2003, 2005; Willeitner 2005a). Natural durability of some bam-boo species against four decay fungi was investigated by Remadevi et al. (2005). The influence of the felling time on resistance is controversially discussed. It has to be considered that fresh winter-felled wood is less susceptible to damage due to other moisture, drying, and climatic conditions than wood felled in the summer. There are however no differences if the wood is carefully dried (Willeitner 2005a). 

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