[header] How to fill in a small area with concrete [title] You will need to dig the area out to a depth of about 3-4 inches (7.6-10.2 cm). [title] Compact the soil below. [step] Use a dirt tamper. 
Make sure the area has no puddles before you pour the concrete. [title] Form the area by using 2 x 4's on their side, thus creating a box or shape that the concrete will be placed.