Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.
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He told me, "If you can build stairs out of wood you can build concrete stairs".
When I was a young carpenter, working on a school project, I was told to build a set of concrete stairs to connect two levels of a sidewalk, not yet in place. I talked to my father who taught me the trade while working on industrial projects in northern Canada, constructing mine buildings and bridges. Somehow I missed the concrete stair session. He told me, "If you can build a wooden set of stairs you can build them out of concrete." He told me two things: the stringers for a concrete stair are on top of the treads and instead of a nosing, the riser is angled to give a wider tread. Armed with my new information, I attempted to build the set of concrete stairs.
To support the stringers, I built the forms on each side of the stairs, braced them properly in order for them to hold the concrete. I built them tall enough to be able to nail the stringers to them. I measured the total rise between the two levels of proposed sidewalk and calculated the individual rise. I used a low rise of 6" for the kids and chose a run of 12" to complement the rise. I learned that in stair building the pairs 6 and 12, 7 and 11 and 8 and 10 went together. I laid out the stringers. I found it tough at first to get my head around the fact that the stringers are above the treads, acting as a support for the risers that are like bulkheads in a form. I canted the riser back 1" on the bottom to allow more room for the foot on the tread. I used 3/4" form ply on the side forms and for the stringers.
Once the side forms were in place and the stringers fastened in position, I could see that the slope of the earth needed a bit of correction. I wanted at least 4" of concrete under my risers. The dirt was removed to form the correct slope and clearance. It was then compacted well using a plate compactor.
Since this was a commercial project and a union job I just stood by and watched the laborer repair the slope. Actually I stood there just long enough to be sure he understood what I wanted. While I was waiting for the preparation of the slope, I continued on my stairs. I ripped my risers to the right heights and the bottoms on a 45 degree. This was another piece of info my father included: "When the cement finisher comes along to finish the treads, if the risers are not ripped to a 45 on the bottom, since they are are on an angle, the bottom will dig into the tread below it". By ripping the riser material on a 45 degree angle, the bottom of the riser comes to a point, allowing the finisher to trowel right up to the inside bottom corner of the tread and riser. Otherwise there will be a depression left of the 2x8 riser along the tread next to the riser.
I returned to the stair site and noticed the foreman had asked the rebar guys to install a mat of rebar to lay on the slope, after the laborer had finished his compacting. I nailed the risers into position. Since the stairs were about 5' wide I tied all the risers together at the center of their span with a 1x4 nailed down the slope attached to the top of the risers. At the bottom of the 1x4, I drove a stake into the ground to prevent them from moving. I also drove stakes at the edge of the side forms to prevent any movement in the same direction. The risers were all attached to the side walls and I could see the force created by the weight of concrete wanting to deflect the 2x8 riser forms. As I was finishing up, I noticed the rebar guy was back and held the mat off the slope by attaching tie wire to it and hanging it off the risers. He formed a loop around the mat and the riser so the cement finisher could cut the wire and pull it out to get it out of his way. He also added a couple of bars running with the risers in each tread.
Concrete was scheduled late in the day so I stood and watched as the laborers poured the concrete. I loved those union jobs. The forms held well. The finisher started to finish my masterpiece. The concrete was setting up quickly in the heat. The finisher wanted to remove the 1x4 tying the risers together. He got me to remove the 1x4. I had to pry it from the risers with extreme care to avoid any movement. I learned a valuable lesson: now I always attach this 1x4 into the riser tops with screws to make it easier to remove during the finishing process.
I've formed many concrete stairs since then. The first one was a good learning experience.
Dave(Ask Dave) (About Dave)
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