Whether you want to add or extend a porch to your backyard, build a new shed or lay a new driveway, you must always prepare the ground before pouring concrete. If you pour concrete on ground that isn't level, the concrete will most likely crack, break apart or sink. Pouring the concrete is easy; framing out the area and prepping the ground can be the difficult part. Depending on the size of the slab, the prep time can take anywhere from a few minutes to a few days.
Collect all of the materials you will need.
Use a measuring tape to lay out the area where the concrete slab will be poured. Add 2 inches to each corner for the wooden frame that will define the area of the slab. Use a hammer to tap a small wooden ruler into the ground at each corner as a marker.
Tie a piece of string from one marker to the next. This provides the outline for the frame into which the concrete will be poured.
Clean up any large objects, such as sticks, garbage or rocks, from the slab area. Rake the area to remove smaller items, such as leaves, stones or mulch.
Use a shovel to dig about 2 to 3 inches down in the marked area. This depth will allow you to pour the concrete level with the ground. Concrete must be at least 2 inches thick to avoid cracking or freezing.
Use a shovel and a rake to smooth the area once you have dug it out. If the area has soft spots, use some of the removed dirt to compress it so that it's be level with the rest of the area.
Place a level in different parts of the slab area to check how level the ground is. If any spots aren't level, fill those in with the removed dirt as needed.
Lay pieces of two-by-four, with the narrow edge facing up, along the edges of the marked-off area to create the frame for the slab. Nail each side together to make the frame secure. Check the level of the ground again before pouring the concrete.
Measure a few times to make sure your frame has not been bumped around before you pour the concrete.