Stair Stringer Layout
The math and framing-square method for cutting stair stringers.
Bevel the Bottom Edge of Concrete Step Forms So You Can Float Under Them
Cut the bottom edge of each riser form board at 45 degrees before you set it — the bevel leaves room to slide a float all the way to the back of the tread below, so you can finish the concrete with the form still in place.
forming concrete stairs, pouring front steps, rough patch under the form board, step edges come out rough
The Problem
When you form concrete steps, each riser board sits down into the pour — an inch and a half or more of the board is buried in the concrete of the tread below it. Set that board with a square bottom edge and you've built yourself a wall: the float can't reach the back of the tread underneath, so the strip of concrete against the riser stays rough until you strip the forms, when it's too late to finish it properly.
The Technique
- Before setting each riser form, rip or cut its bottom edge at a 45-degree angle, with the bevel opening toward the tread below.
- Set the form as usual — the face of the board still defines a crisp riser face, because the top of the beveled edge is what molds the concrete corner.
- When it's time to finish, the bevel gives your float a clear path: you can reach in under the form and float the tread surface all the way to the back, with the board never sitting down in your mud.
Small cut, big difference: every tread gets finished edge to edge while the concrete is still workable, and the risers strip clean.
Pro tip: This is one of those details that separates great concrete work from mediocre — not because the bevel itself shows, but because the finishing it allows does. Anywhere a form buries itself in a surface you need to finish, ask whether an angled edge would let the tool in.
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