Repairing Holes in Concrete
The first thing you want to do when repairing large holes in concrete is to break out all of the damaged area with a sledgehammer or jackhammer. Remove the large pieces. The edges of the hole should slope towards its center - you can create this effect using a hammer and chisel. Then, buff the edges with a wire-bristled brush to remove loosened particles.
Remove a few inches of the dirt floor below the concrete slab, deepening the hole. Then, with your sledgehammer, pound the dirt so that it lies smooth and is tightly compacted. Cover the dirt with a layer of gravel up to the bottom of the subfloor.
Place wire mesh, cut to size, in the hole. It should rest against the angled sides of the concrete. You may wish to place large rocks or bricks underneath the wire mesh in order to hold it in place when the concrete is poured.
Apply a good layer of an epoxy bonding agent to the inside edges of the hole. Then pour the concrete, making sure that it fills all crevices, cracks, and meets the sides of the hole. Use a wire coat hanger, a rake, or another hooked tool to pull the mesh up through the concrete, so that it floats about halfway down from the surface of the newly-poured floor.
Smooth the concrete with a 2x4, preferably working with a partner. If you find that your concrete seems uneven, you can add a couple of shovelfuls of concrete to the patch to maintain a smooth surface.
When the concrete begins to look dull, it is ready to be smoothed for the final time. While the patch cures over the next few days, make sure that it stays moist by sprinkling it with water and keeping it covered with a sheet of polyethylene.
Your repaired concrete floor is now ready to take a new surface!