Concrete – Fixing void on face of concrete steps

You need to construct shuttering (usually timber) to hold the concrete in position while it cures. You'd usually have the shutter that forms the face of the stair "open" to allow concrete under to the lower step.

( This shows the principal )

If you use a stiff mix of concrete, it won't flow under the shutter forming the face of the stairs, but you will have to work harder to compact it to get a good finish. If you do find the occasional air void when you remove the shutter, you can fill in with a cement mix.

One solution, if you have some space to work with at the foot of the concrete steps, is to add some new steps constructed with pressure treated lumber. Here is an example to convey the idea.

The unevenly spaced original steps are replaced with a new set that are evenly spaced from the ground level up to the top. In this example I show the use of 2x12 lumber to create both the steps and the stringers under the steps. You could place the stingers to the outside edges of the existing concrete structure or notch them as necessary to fit over the nose of the existing concrete steps.

Not shown in this concept drawing is a header that would be secured between the top ends of the stringers under the new step. The header would be flat against the riser of the existing top step. Fasteners through this into the existing concrete would secure the new timber structure.

Another advantage of this concept is that many old style steps do not have adequate landing area at the top to make it easy to negotiate opening a outward swinging screen/storm door. The added width of the top step can help with this problem.