Little did I know, when I made my first visit to the site on a mild Friday in May, that the owner would already have a job lined up for me. I expected to get the lay of the land and discuss scheduling, but I’m mighty glad I brought my work gloves. They first broke ground early this week, and by Friday the excavator had graded a gravel driveway (which will become the final driveway), filled a stone pad to serve as foundation for the Barn, and erected formwork for the 40×30 concrete slab. Our task for the day: brace the formwork so it will hold in 23 cubic yards of wet concrete.
We braced the form with 2×6 timbers screwed flat at 4-foot intervals around the perimeter. Contractor rule of thumb, apparently. Now I trust this particular contractor with my life, but you can’t spend five years in a structural engineer’s office without learning to check every rule of thumb you come across. (I’m a professional skeptic.) So when I got home I convinced myself mathematically that a 2×6 has ample strength to hold back 9 3/4 inches of wet concrete. So far, so good. After the concrete sets, we’ll reuse the braces as floor joists in the Barn, which is pretty cool.
The hardest thing about installing the braces was making physical space for them. The sloping site drops off more than 3 feet from the back of the Barn, and I had to shovel trenches through the stone pad so the braces could sit straight between the form and the ground. The 1/2-inch gravel surface gave way easily enough, but the 5-inch cobbles below proved more stubborn. In the end we left one 8-foot gap where even a 12-foot-long brace wouldn’t make it down to grade, and further supported the form with a gravel berm all around the outside.
We anchored the braces by driving stakes into the ground and attaching them with screws. Before making each connection we checked that the form was straight, plumb, and square. If any location looked a little off, we applied pressure (by leaning our body weight against it) to hold the form where we wanted, and saw that the shape held once the brace was anchored.
Finally we removed one brace at the front where the grading machine will drive in after the concrete is placed (and where the main garage door will eventually go) and put away our tools expecting lots of rain over the weekend. A satisfying first day.
And just to give a taste of the variety you can expect in this blog, here’s my volume calc for the concrete delivery Monday. Our order doesn’t allow any wiggle room, that’s for sure.