Improvements to Water Vapor Transmission and Capillary Absorption Measurements in Porous Materials

Abstract The vapor permeability (or equivalently the vapor diffusion resistance factor) and the capillary absorption coefficient are frequently used as inputs in hygrothermal or heat, air, and moisture (HAM) models. However, it has been well documented that the methods used to determine these properties are sensitive to the operator, and wide variations in the properties have been reported in round-robin testing. This paper presented an investigation into how these errors can be minimized for porous materials by different edge sealing techniques and also looked at whether automating these techniques can reduce operator artifacts. To automate the measurements, specimens were attached to a balance or load cell and then required no further interaction, which allows massive amounts of data to be collected. The extra data is advantageous for the beginning of the capillary absorption test where the moisture uptake is rapid. Most of the potential for errors in the vapor diffusion tests resulted from uncertainties in how the sample was sealed between the chambers and determining when the steady state region was reached, neither of which can be improved by automation.