Effects of drying conditions, phase transformations, and carbonation reactions on measurements of sorption isotherms of building materials

The sorption isotherm is one of the basic material properties used in hygrothermal modeling of building envelope performance. Measurement of this property Is deceptively simple. Specimens are first dried and then exposed to a series of higher relative humidities to develop a curve of moisture content versus relative humidity at constant temperature. This paper discusses some confounding effects that we have observed while performing measurements on a number of common building materials. Materials studied included gypsum products, wood and wood products, and cementitious materials.