This report describes the construction of multicomposite ultrathin films using the layer-by-layer assembly technique. The films are built-up with two different architectures: with and without a layer composed of the inorganic nanosheets of the clay mineral montmorillonite. Using two techniques of characterization, neutron reflectometry (for deuterated polyelectrolytes) and absorbance spectroscopy (for ion-sensitive dyes), it is demonstrated that the mineral layer acts as a barrier for the transport of ions along the film normal.