How to Build Forms for Concrete Stairways

Making the Form

• 1

  Determine the size of the steps you want to use. For a step height (rise) of 4 to 4 1/2 inches, the tread depth should be 18 to 19 inches. For a step height of 5 to 5 1/2 inches, the tread depth should be 16 to 17 inches. For a step height of 6 to 6 1/2 inches, the tread depth should be 14 to 15 inches. For a step height of 7 to 7 1/2 inches, the tread depth should be 10 to 11 inches.

• 2

  Cut the side pieces for the form, known as stringers, using step dimensions from Step 1. Slope each step downward about one-quarter inch so that water can run off. Use one-quarter-inch plywood. Angle each stringer so that the bottom edge slopes upward. You will be making concrete stairs that rise upward rather than a solid mass of concrete.

• 3

  Cut the one-quarter-inch plywood that will support the underside of the stairs. Choose the stair width you want, but avoid making it wider than 3 feet for this project.

• 4

  Attach the plywood support to the stringers with duplex (double-headed) nails. The plywood support should extend 1 foot wider than each stringer.

• 5

  Nail pieces of 1-by-4-inch wood to the exterior of the form, bracing the stringers against the plywood support. Put the bracing blocks every 2 feet.

• 6

  Saw 2-by-8-foot boards, rip them lengthwise to match the height of the rise, and nail them to the front of each step to keep freshly poured concrete inside the form.

• 7

  Lay the form on top of the support built in the next section.

Building Support for the Underside

• 8

  Saw 4-by-4-inch posts and place them upright on 1-inch thick squares of wood for later removal. You'll need at least four, possibly more, depending on stair height. Cut the tops at an angle to match the upward angle of the concrete stair form.

• 9

  Lay 4-by-4-inch posts atop the vertical 4-by-4's, nailing them in place. These posts will provide support under each stringer as it angles upward.

• 10

  Add support across the width of the stair by putting 2-by-6 boards across the 4-by-4's added in Step 2. Nail the boards together.