Lamellar calciumaluminatehydrates are products of the hydration of ordinary Portland cement and play an important role in its hardening process. Due to the fixation ability of inorganic ions the technical features of this lamellar phases are important as reservoir minerals for pollutants (storage minerals). The lamellar calciumaluminatechromatehydrate Monochromate with the idealized formula C3A.Al2O3.CaCrO4.Ca(OH)2.nH2O has been investigated using a Philips Diffraction System X'Pert with the X'Celerator detector to measure the kinetics of the changes in interlayer dimensions in the lamellar calciumaluminatechromatehydrate at room temperature in air. A certain amount of water is weakly fixed in the interlayer depending on the interlayer anion, temperature and relative humidity of the atmosphere. Processes like ion exchange or water-loss in the interlayer cause a variation of the crystal dimension in c-direction. These "processes" can be very fast, therefore an ultra fast data collection and measurement times less than 2 minutes from 2° 2Θ to 70° 2Θ were essential.