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Now that you know the general dimensions of your steps, you can stake out the area where you will be building your steps. Hammer a wooden stake into the ground at each corner of the base of your stairs.  Measure from corner to corner to ensure that your layout is properly squared up and the dimensions are correct. To make sure that your stakes are evenly lined up, run a length of string between the stakes around the perimeter and use the string to verify your stakes are aligned properly. Not running a line between your stakes to keep alignment can lead to more work on your part. In the worst-case scenario, a poorly aligned perimeter can result in a slanted/angled finished product. You'll need to use a shovel to dig 4-8" (10.2-20.3 cm) below the ground level of the base of your stairs. Dig within the boundary of the string you've set up to prevent digging any more than you have to.  This excavation is intended to clear away rocks, trees, grass, shrubs, and anything else that might interfere with your concrete pouring. You'll also have to lay a sub-base upon which the concrete will rest. Since your sub-base  should be at least 4-8" (10.2-20.3 cm) thick, you'll need to dig down at least this far or the rise of your first step will be larger than you plan. Using the dimensions you've taken for your staircase, cut pieces of scrap wood or low-grade lumber so you have a board for the rise for each step and two boards for the stringers (one for each side of your stair form).  Use 2 in × 6 in (5.1 cm × 15.2 cm), 2 in × 8 in (5.1 cm × 20.3 cm), or plywood that's 3⁄4 in (19 mm) thick. Your form should exclude the top and bottom of the entire stair. The ground-oriented side of your stringer forms should be cut to meet the pitch line (angle) of your stair, and the top should be cut in a zigzag fashion to follow the rise and depth of each tread (step). If you are pouring concrete steps that form a right angle (L-shape), your stringer forms will not need to be cut on an angle. In this case, your stringer will follow the entire run and rise of your stairs. You should shave a slight angle into the bottom of each rise form board, excluding the bottom riser form board. This way, when you pour your concrete, you'll be able to easily smooth the area in the corners of each step. Use screws and a power drill to attach each riser form board to your stringers. You can do this by laying each stringer form so the even, bottom side of each stringer is flat on the ground and the zigzag side of the stringer is oriented with its points facing up.  Screw 2 in × 4 in (5.1 cm × 10.2 cm) planks into the form and fasten them to the ground with wooden stakes to prevent the form from bowing out. Space your stringers to be approximately the planned width of your stairs apart. Then you can lay the riser form boards along the zigzags of the stringer that matches the upward rise of each step. Now you should be able to easily use your power drill to attach each riser form board to the stringer form boards. If your stairs form a right angle (L-shape), you should be able to lean them against a sturdy object base down so each stringer form is oriented like a normal stair. You may have to place a board between the stringers to stabilize them until you screw your first riser form board into place. Be sure there are no gaps in your form and that the boards line up evenly. Any gaps can lead to concrete leaking through your form, and unevenness will result in uneven steps. When you look at your form from the side, it should look like finished steps. Your concrete steps will lie upon a subbase of granular fill, like open-grade stone, which will protect your poured concrete steps from shifts in the earth or deterioration. You'll need between 4-8" (10.2-20.3 cm) of fill for your subbase.  After placing your subbase, you'll need to tamp it down until it is packed extremely firm, level, and stable. Use a long flat board and a level to check the levelness of your subbase. Smaller projects can likely be done with a hand tamper, which is essentially a heavy, flat metal plate attached to a wooden handle. Larger projects might require you to use a plate compactor machine. Failing to lay a sturdy subbase can result in cracking, deterioration, or structural failure in your concrete steps. Your concrete's strength depends on a solid subbase. You may want to lay a thick gauge wire mesh on top of your subbase to reinforce the concrete you'll be pouring. The idea is, even if your concrete cracks, the mesh will hold it in place so integrity of your stairs is maintained.  If you live in a colder climate, you can apply a layer of Styrofoam 2 inches (5.1 cm) deep before adding gravel so frost doesn't freeze underneath your steps and damage them.
Stake out the base of your steps. Excavate the area where your steps will be poured. Cut the pieces for your form. Assemble your concrete form. Lay your subbase.