When patching a concrete floor, it is important to choose the right product. Cracks less than a half-inch wide should be filled with a liquid concrete sealant or a concrete caulk product. Larger cracks and holes should be filled with a sand aggregate concrete mix, and holes more than 1 inch deep should be filled with a gravel aggregate mix.
Step 1: Use a cold chisel and hammer to smooth the rough edges of the concrete and break away any loose particles. Set the chisel at a 45-degree angle along the edges and enlarge the lower portion of the hole enough to make the bottom of the hole larger than the top.
Step 2: Use a coarse brush, vacuum, compressed air or any other means necessary to remove all the dust and debris from the hole.
Step 3: Thoroughly coat the area to be filled with a liquid concrete bonding agent.
Step 4: Once the bonding agent is tacky, fill the hole with the appropriate patching product. For larger holes and cracks, press the cement mixture into crevices and along edges before filling in the main portion. Leave a fair amount of concrete mounded above the surface of the crack or hole.
Step 5: Use a wooden board, wider than the hole, to level the mounded concrete. Moving the board back and forth in a sawlike motion will compact the material better than simply troweling over it.
Step 6: After about an hour, as the fresh concrete loses its sheen, smooth the area with a magnesium or wooden trowel. Feather the new material to blend it in with the existing concrete.
Step 7: Once the concrete has hardened, in approximately two or three hours, mist the concrete lightly with water and use a metal finishing trowel to burnish it or a wet, stiff-bristle brush to texture it.
Clean your tools off immediately and wait at least 24 hours before walking on your newly patched concrete.