Trotec T500 Manuel D'utilisation page 53

Gypsum plaster
The determination of the moisture content of gypsum plaster is a
special case. As can be seen from the following diagram, the vol-
ume-related moisture content of gypsum plaster changes little at air
humidity values from 0 to 80%:
Sorption
isotherms of
gypsum plas-
ter
Relative air humidity ϕ
Above 80% the moisture content changes rapidly. This has been
confirmed by calibration measurements carried out by the Institute
of Building Materials Research (IBAC). Accordingly, it can be de-
duced that a direct correlation between measured value and mass-
related moisture content is not possible. However, as a sufficient cri-
terion for classifying the measured values, it may be said that
gypsum plaster can be described as "dry" if the resistance value is
smaller than 30 digits. In evaluating the measured values, it is es-
sential to note that different marginal conditions exist for each
Water content
measurement.
u in %
v
Additional factors which influence the size of the measured val-
ue are the coupling of the electrodes to the measured materi-
al, the composition of the building material, the salt content and
the aggregates.
Operating manual – English
B - 20