Pouring concrete over concrete
Q. I am going to pour 2" of concrete over a 4" cracked slab of concrete behind my back door. If I put wire mesh down first will the concrete I pour crack with such a deep base already present?
A. If the crack in the bottom slab is still active, meaning the bottom slab still moves (expansion & contraction), it is highly likely the crack will mirror through the new 2" of concrete.
If the bottom slab is not moving, it shouldn't crack in the same spot, but possible it may crack somewhere else. If the slab is larger than 8' x 10', I would saw some contraction joints to help prevent it from cracking. If the slab is smaller than this you should be ok.