Comprehensive protection of timber in seawater
The hazard of wood in seawater can be divided into two areas: Below the water level, shipworm (Teredo navalis) and gribble (Limnoria lignorum) can attack non-resistant or insufficiently protected wood; above the water level, there is a risk by wood-destroying fungi and, to a lesser extent, insects. In a national project funded by the Deutsche Bundesstiftung Umwelt (DBU, German Federal Environmental Foundation), in addition to various laboratory, field and practical experiments, the infestation risks, pest occurrence and protection possibilities of native coniferous wood species were investigated. However, the main focus of this paper is on laboratory studies on the fungicidal effectiveness of sea salt (sodium chloride) against basidiomycetes and in this context the distribution of sodium in roundwood after exposure in artificial sea water. The fungal tests according to EN 113 (1996) against the basidiomycetes Coniophora puteana, Poria placenta, Gloeophyllum trabeum and Coriolus versicolor prove that the mass loss is less than 3% at application rates above 15 kg NaCl/m³. The chemical analyses show that 20 cm above the water level an average sodium content of approx. 40.000 ppm (or the equivalent of more than 40 kg NaCl/m³) was quantified over the whole pine log cross-section, which is significantly above the derived fungicidal threshold value of 15 kg/m³. In addition, a brief overview of the results of field studies and observations on wooden constructions that were partially exposed to seawater in practice is given.