@Wash, the amount of signal attenuation in concrete various from 12-27db. This is a huge loss, and if the concrete has metal in it, the attenuation increases. The other problem is that throwing a strong signal at it is going to cause various reflections and noise therefore you could end up with a very slow connection with large dropouts due to errors, no matter the signal strength. Since you are in the floor, give power-line ethernet a try if you can find the devices locally. :-)