As far as I know it's only reinforced concrete walls. As for frequencies I have nfc.
Concrete walls usually have iron bars inside as reinforcement. Since the walls are earthed, that will work as a Faraday cage, shielding you out of the wifi signal. :\
^
Is it "wireless N" or "wireless G" (technically N can be 2.4 as well or dual band), then there's AC which I believe (could be wrong as I'm going from memory) is only 5ghz. But yeah if it's reinforced concrete even on the inner walls you may just be boned, you could put in a switch and have an AP in each room, but you'd have to have it professionally done, or learn how to do it (it's not that hard).