SORPTION HYSTERESIS AND SCANNING IN A FLOORING SCREED - IMPLICATIONS FOR MOISTURE INDUCED DEGRADATION

摘要

Sorption isotherms (moisture content as a function of relative humidity (RH) at equilibrium) are an important tool in designing buildings to limit moisture related problems. Normally only a single sorption curve is used so that each moisture content uniquely corresponds to one RH. Sometimes two curves are used, one curve for absorption and one for desorption, as it is well known that sorption has a strong hysteresis for most materials. However, in most situations, materials do not simply follow either absorption or desorption, but will follow scanning curves within the hystersis envelope. In this paper we discuss data on sorption hysteresis and scanning for a cement based flooring material. These data show that the RH-increase will be many times higher when the flooring material absorbs moisture from, e.g., water based adhesives, than would have been predicted by a model without scanning. Implications for expressing critical moisture levels are discussed.