Simply filling a hole in a concrete floor with a concrete mix will not permanently repair the hole. In most cases, the concrete will break loose, and you will be performing the same job over again. Patching the hole correctly the first time will take some preparation and effort on your part. The tools to perform the task are basic, along with the products required.
Remove all of the broken concrete with the hammer and chisel. Level the bottom of the hole and undercut the sides. The undercuts will aid in retaining the concrete patching material for the long run.
Vacuum the hole to remove all loose material. Wash the hole with the garden hose. The hole can remain moist, but remove all standing water.
Coat the interior surfaces of the concrete patch hole with the bonding agent. Follow the label instructions as to application rates and disposal of the excess material. Some bonding agents may come in a spray bottle, while others may have to be brushed on to the surfaces.
Mix the concrete patch material according to label directions. Various products exist on the market with different mixing processes.
Fill the hole with the concrete patch. Work the material into the corners of the hole with the end of the 2-by-4. Level the material in the hole by straddling the hole with the edge of the board. Drag the board across the hole, moving it side to side to level the material.
Smooth the concrete material with the hand trowel. Allow the material to cure without foot traffic for at least 24 hours or according to label instructions.
If the concrete floor is outdoors, place a sheet of plastic over the material as it dries. The plastic sheet will retain moisture for a slow cure. The plastic will also keep rainfall from washing out the fresh concrete. Keep all vehicle traffic from the area for a period of five days. Temperatures below 10 degrees C will cause the concrete to take longer to fully cure.