Electron paramagnetic resonance (EPR) associated with adsorption gravimetry and X-ray diffraction (XRD) has been used simultaneously to study the dehydration process in a Cu2+-hectorite. The combination of these three techniques has provided information concerning the nature of copper hydrates, the total water content and the clay layers’ stacking order. Three copper hydrates are detected depending on the relative water vapor pressure : bare unhydrated ions in an isotropic environment, square planar tetrahydrates, and octahedral hexahydrates. "Pure" hydration states are observed at P/P-0 = 0.40 (tetrahydrates) and P/P-0 = 0.99 (hexahydrates), concomitantly with regular stacking order. Interstratification is observed in all other hydration states. A significant amount of water is found to be located outside the interlayer space, even after extensive evacuation at room temperature. A model of connected clay platelet stackings is proposed, which accounts quantitatively for the amount of water both inside and outside the interlayer space.