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The influence of microclimate on the moisture conditions in a Norway spruce (Picea abies (L.) Karst.) joint exposed to artificial rain
2013 - IRG/WP 13-20505
Wood structures outdoors are susceptible to decay if they are exposed to high moisture contents during long periods of time. Structures with joints that act as water traps are especially exposed since high moisture contents are reached in such positions. This paper presents a part of a laboratory study that concerns the relationship between the microclimate and the material climate, i.e. the moisture conditions at the surface and the wood moisture content. Norway spruce (Picea abies L. Karst.) joints of different designs were exposed to artificial rain in the laboratory and the duration of water in gaps and on surfaces were monitored as well as wood moisture content profiles. This paper presents moisture content measurements in one joint from this study. The joint consisted of one vertical and one horizontal board and to create different moisture conditions at the surface, three joints with three different gaps (0 mm, 2 mm and 5 mm) between the vertical and the horizontal board were used. These three joints were wetted using two different watering schedules: one long wetting period (6.5 hours) and wetting in cycles (1 hour every twenty-four hours). In some cases, the moisture content during and after the wetting was high irrespective of gap size. However, the moisture content in the specimens with no gap or a 2 mm gap remained at a high level during a longer period of time than the specimens with a 5 mm gap. In other cases, the 5 mm gap gave lower moisture contents also during the wetting periods. In general, the duration of moisture contents above 25% was lower in the specimen with a 5 mm gap, but the magnitude of the reduction varied.
M Fredriksson, L Wadsö, P Johansson