Experimental techniques were developed for measuring moisture diffusion coefficients of building materials. Results were obtained for white pine, gypsum board, and a latex paint coating at nominal ambient temperatures of 76 deg F and 44 deg F. Moisture transfer rates were measured using a modified ASTM permeance cup procedure. The modifications were implemented to investigate the dependence of moisture diffusivity on moisture content and to take into account the effects of external transfer resistance. Diffusivities were correlated with moisture content using an exponential relationship. The measured diffusivities for both materials depended strongly on moisture content and temperature. At 76 deg F, the diffusivity for white pine increased almost an order of magnitude, for a 20% increase in moisture content (dry basis). The diffusivity of gypsum board decreased by approximately two orders of magnitude, for a 2% increase in moisture content at 75 deg F. At the same moisture content, the diffusivity for white pine was about three times greater at 76 deg F than at 44 deg F. For gypsum board, the diffusivity was from two to six times greater at 75 deg F than at 44 deg F. Moisture transfer rates were also measured for gypsum board specimens with two coats of latex paint on one surface. The data were analysed to determine the permeance of the paint layer. Permeance was also found to depend strongly on ambient relative humidity. At 75 deg F, the permeance increases by approximately a factor of six as the average ambient relative humidity increased from 20% to 90%.

KEYWORDS: measuring, moisture, water permeability, buildings, materials, gypsum plasterboard, paints, ambient temperature, relative humidity