The radiowave propagation through hollow clay brick walls, which are common in Southern European construc- tion, is analyzed. The brick walls have thicknesses of 11, 15 and 20 cm, common in both interior and exterior walls, and are bound with a portland cement, water and sand mixture. For each brick dimension, three prototypes were assembled, varying in the type of wall finish, i.e.: exposed brick, smooth painted plaster and rough painted plaster. A 10cm concrete wall was also included for comparison purposes. Penetration loss metrics were evaluated in an anechoic chamber at frequencies ranging from 680MHz up to 10GHz. Results demonstrate that the brick wall internal heterogeneity, as well as the type of finish, significantly influence the propagation phenomena and thus the frequency response of the walls, with relatively high penetration losses observed at some relevant commercial frequency bands. Finally, an alternative brick design, with reduced penetration losses, is also proposed and evaluated under simulation environment only.