The invention is a process for determining the resistivity of a layered structure including a layer of resistive material hidden under a topcoat and a tile layer, the process comprises the steps of; 1) directing electromagnetic radiation over a selected frequency range to the outer surface of the layered structure; 2) measuring the reflection of the electromagnetic radiation from the layered structure surface; 3) converting the signal into the time domain; 4) analyzing the first echo to obtain the topcoat thickness; 5) obtaining the tile thickness from the time delay between the first and second echoes; 6) compensating the second echo with electromagnetic power loss due to the topcoat and tile; and 7) determining the resistance of the resistive layer from the compensated second echo.