Why can you pour concrete over concrete?

November 2, 2007

We have a 12 X 35 concrete patio in the back it was poured in several sections over several years. The original portion is rock solid. The later sections have sank about an inch and were poured over the top of a septic tank. We are going to remove septic and repair/replace the patio with something uniform. The price quotes for removing the tank and concrete have been crazy. I have been told by several people that I can not just pour concrete over the top of the existing patio after the tank has been filled in. I want to know why not. I have been told can not pour concrete over concrete but i want to know why. I have told it will not bond but I want to know ehre the heck a slab that big would go. Why can't you pour concrete over concrete?

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