Equilibrium moisture

From Saltwiki

Author: Hans-Jürgen Schwarz
English Translation by Sandra Leithäuser

back to Physical Principles of Moisture


The equilibrium moisture content of a material is a function of the moisture content of the ambient air and temperature. It is defined by the maximum moisture a material can hold at a certain relative humidity and temperature in equilibrium with its environment

Similar to the equilibrium moisture content of a salt, the equilibrium moisture content of a sample may be defined as follows:

The equilibrium moisture content is the mass-related moisture content of a material at constant boundary conditions.

The sample does not become wetter or dryer. It is thus clear, that the determination of equilibrium moisture content can be more important than the determination of the actual moisture content. In many materials the change in moisture causes expansion or contraction, which then causes damage. If the moisture of the ambient air differs from the equilibrium moisture it re-occurs through moisture uptake or release. The equilibrium moisture content of a sample decreases with temperature increase.