Are you referring to cut lines in the concrete? If so without cut lines the concrete will crack. The client for this project did not want any cut lines and did not mind having some cracks.

The concrete floors are beautiful. We just put a concrete floor with radiant heat in a small addition (10'x17'). It was poured last April. Our contractor told us to expect hairline cracks, as we don't have any expansion joints either (except at the perimeter). All was great until yesterday morning my husband heard a loud pop from the next room. There is now a crack down the entire center of the floor, and it looks like there are cracks which are beginning to radiate from that crack. I'm heartbroken and very nervous about what might happen to the rest of the floor. Any advice? Thanks.