What about expansion joints? Are they covered up?

Expansion joints and cold or control joints are necessary to prevent cracking of the concrete. Concrete must be allowed to expand and contract with temperature changes. These joints provide a "controlled crack" for this movement. All expansion joints are left in place, we cannot cover them up. We also re-cut all existing joints a little deeper to ensure that when it does move, it moves where we want it to, and not at a different weak spot in the concrete.