We fabricated thick films of cubic garnet solid electrolyte Al y Li7-3y-z La3Zr2-z Ta z O12 (ALLZTO) by the Aerosol Deposition Method (ADM). Due to the room temperature impact consolidation (RTIC) mechanism, the films become dense. A thermal post-treatment of the film revealed the morphological and process-related impact on the ionic conductivity. As-deposited films show a reduced conductivity around 2·10−7 S/cm. Using electrochemical impedance spectroscopy and high-temperature X-ray diffraction, we found the lattice distortion and nano-crystallinity of the films to be the decisive effect for the conductivity reduction. In our case, post-deposition annealing at 400 °C lead to an increase of the ionic conductivity to 2·10−5 S/cm. With a beginning of sintering at 600 °C, the conductivity successively increased further, reaching values of 7·10−5 S/cm.