 It really just shouldn't be sitting on the four-inch concrete slab. It should be sitting on the footing below it, be that what it may. Another idea that you might want to consider is PaveStone makes a paver brick that is about half the thickness of a full paver brick. And it's designed for taking a cement slab that maybe doesn't look so hot and creating a beautiful paver patio with it. The way it works is...