Concrete stairs are typically made for outdoor locations such as the entrance to houses, gardens, hills with a slight slope and between elevations on golf courses. The curved outdoor steps described here can be adjusted slightly for indoor installation, but you have to add a plastic sheet on the plywood floor to prevent it from becoming soaked with moisture from the drying concrete.
Plan your stairs. Each tread or step should be 10 to 12 inches deep. Each riser, the height of each step should be 6 to 8 inches. If you have a wide bottom step, or landing, it should be 3 feet deep.
Level the ground for the bottom step.
Measure and rip Masonite for curved forms. Cut the forms ½ inch higher than your steps because you will fill them with concrete 1/2 inch short of the top.
Measure and cut 1/2-inch sheets of plywood for the side forms. The side forms should be deep enough to accept concrete fill below ground level.
Measure and cut 2-by-4 stakes to hold the plywood side forms in place.
Laying the Concrete
Use concrete blocks to hold the curved Masonite forms in place. Nail the plywood side forms to the 2-by-4 stakes. Nail from the inside out.
Put a ½-inch layer of quick-drying concrete on the bottom of the step and rake it level. Spray with water until it is saturated.
Cut wire mesh to fit the interior of your form and lay it on the bottom layer of concrete. This wire mesh will help prevent the concrete from buckling or cracking in areas with severe freezes.
Add the concrete mixture in 1-inch layers, saturating each layer with water. Let the concrete stand for 5 to 10 minutes between layers. Adding the concrete in layers helps prevent the concrete from bending or warping the forms with sudden weight.
Let the bottom step cure for 14 hours or more in a temperature above 65 degrees Fahrenheit.
Dig back 24 inches from the top of the first step. Repeat the process of cutting and installing forms, adding concrete and allowing to dry. Do this for each step all the way to the top.
Finishing the Steps
Apply a finish layer to the top step with a quick-drying concrete mixture that contains sand rather than aggregate. Mix it with the drill and mixing blade. After you spread it, run a two-by-four across the top to level it. Use a trowel to smooth off the surface.
Use a broom to give the top a slight texture so it won’t be slippery when it is wet. Round off the sharp edge of the steps with a concrete edging tool.
Repeat the finishing process for the remaining steps. Let the top layers sit for at least 14 hours, then remove the forms. Keep the stairs damp for 5 to 7 days. Concrete that has been kept moist during curing will be about 50 percent stronger than concrete exposed to dry air.