current codes, if rigidly enforced, preclude highway bridge painting on site throughout the winter and much of the spring and autumn in an average year. the temperature must be not less than 4 deg c and the relative humidity not above 90 per cent. as the real criterion is to avoid painting on wet surfaces, a change of emphasis away from relative humidity measurements is suggested. a simple wetness detector has been developed using the principle of a resistance change between two electrodes in the presence of moisture. the complete system enabling readings of surface wetness, air and surface temperatures was installed at various bridge and experimental sites for a period of three years. the results show that the painting season for some structures can be economically extended to the period of march through until the end of october.(a)

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