Deck Stairs—Step By Step
First, mark the perimeter of the slab with stakes and string. Make sure it is deep enough to completely support the mitered bottom of your stair stringers. Then, calculate the depth of the finished slab, including concrete and gravel base, and excavate the soil necessary to place the finished surface of the concrete about an inch above the ground.
The first layer of my slab consisted of 5 inches of gravel compacted down to 4 inches with a hand tamper. Next, I laid a grid of rebar on wire brackets that float the rebar about midway deep in the concrete forms. I tied the rebar intersections with wire. Then, I screwed together the rectangular concrete form from 2-by-4s. I leveled the form on the gravel bed and staked it in place every 18 inches from the outside of the frame.
There was a slight grade in the soil I had to overcome to ensure that my stair landing was built level. To accommodate the slope I partially buried one end of the form below grade, with just the top inch of the form above ground to shed water. The opposite end was set above grade, with the edge of the form exposed. These two alterations allowed me to level it from left to right and front to back, and stake it securely. Be sure the form is flat to achieve an even landing for the stair stringers.
I mixed up some quick-drying concrete, one bucket at a time, and filled my form. It took longer than expected and next time I’ll rent a concrete mixer. You should spray down the form and the gravel with water when adding the concrete. Keep the entire work area damp throughout the installation of the concrete. When it reached the top of the forms, I struck off the excess concrete even with the top of the forms by screeding it with a very straight 2-by-4. I then used a wood float to work the heavy aggregate below the concrete surface and bring the “cream” to the top. Allow the concrete to cure for a few days. Because I was building during the heat of summer, I kept the slab covered in plastic to retain moisture for a slow, solid cure.
While the concrete dries, you can cut the stringers. Traditional stair-building methods require cutting notches in 2-by-12’s to support the stair treads. Laying out the correct measurements can be difficult, and the cutting process can be very time-consuming. However, by using the metal stair brackets, I only had to determine the length of the stringers and the angle of the end cuts. Also, the stringers can be made from 2-by-6’s rather than 2-by-12’s. Making things even easier, I already had the run and the slope of the stairs provided for me by the GoPro calculator.