Why would a zone have striping ?
Striping will always occur, it just depends on the severity. When pumping hot water through the floor, striping will depend the conductivity (or there lack of) of the surrounding material. So, Warmboard, with aluminum, striping is minimal because the heat is spread out quickly and evenly across the metallic surface. Tubing in concrete is much slower. Tubing in concrete with wood sleepers slower still. To overcome the insulatory qualities, systems use increasing hot water to increase heat transfer. But this cause increased temperature differentials across the surface of the floor. This of course makes the system increasingly less efficient. It can also mean you will feel the difference in floor temperatures as you walk in your home. In dealing with hardwood or tile, these inconsistent surface temperature can cause the wood or stone material to expand and contract at uneven rates, causing warps, squeaks and cracks.