ABSTRACT
The EUREKA-project EU 455 Eurocare Prowood aims at developing environmentally friendly surface coatings for protection of exterior wood materials. The project is coordinated by the Norwegian paint manufacturer Jotun AS. As part of this project the effects of microclimate on moisture conditions in coating and wood substrate are being studied. Sawn test panels of Norway spruce (Picea Abies) with different pretreatments were coated with two types of top coating, a water-borne acrylic/alkyd and a solvent-borne alkyd as a reference. The panels were prepared with various moisture sensing devices, all of which were hooked up to a WETCORR-equipment. The types of sensor employed include nail electrodes with the tips positioned close to the surface as well as in the middle of the panel thickness, platinum-wire electrodes embedded in the topcoat, painted and unpainted time of wetness (TOW) sensors mounted on the surface, including surface temperature transducers, and also unpainted sensors built in from the back of the panels but positioned close to the front surface. All test panels were end-grain sealed using Al-primer. A total of 16 panels are being monitored at the exposure site of the Department of Built Environment, Gävle, Sweden. The exposure environment is characterised in terms of air temperature, relative humidity, ultraviolet radiation (UVAB), wind speed and direction, rainfall and TOW, both according to ISO 9223 and WETCORR. The results presented in this paper cover the first 16 months of exposure. To date, the different coating systems have shown only very small differences in wetting and drying characteristics. Despite extensive periods of rainfall and high relative humidity, moisture uptake of the panels has been very limited. Subsequent periods of drying have shown that the different coatings, including the wood substrate, rapidly resume to low moisture levels in conjunction with the decrease in relative humidity.
