Trying to Find Square by Myself
Tue, May 14, 2019On Saturday, my brother and I failed to find square for our foundation layout. We faced a number of challenges, but mostly this is because we cannot easily pull a diagonal, given that we’re dealing with varying grades. Since we left on Saturday, I’ve been considering what went wrong that day, and how it could be fixed. Now I have the added challenge that I am here by myself.
There were two mistakes that I saw we were making (and a third that I will not realize until tomorrow). First, our laser has a margin of error of 1⁄8 inch at 60 feet. We’re shooting at 58 feet, so we should expect to be off by up to 1⁄8 of an inch. Well within the margin of error for footings. However, we have the laser detector attached to a pole that my brother is trying to hold plumb. His ability to hold plumb has its own margin of error. I would say its up two inches or more. We should have been using a 6 foot level stacked against the elevation pole, but we were using a small bubble level that came on the laser detector (unreliable). So our total margin of error for a single shot is at least two inches.
Secondly, we were walking the laser around the foundation, shooting at each corner to find the next. Each time we move the laser to the next corner, the margins of error compound. By the time we were at the third corner, we’re dealing with 6+ inches of error. We should have only shot the two opposite corners (either side of a diagonal) and intersected our lines to find the other two corners.
Being up here by myself forces me to be a bit more rigorous in the setup, and that should greatly reduce our first cause for margin of error. To do that, I stood a 2x4 up vertically and ensured it was perfectly plumb.
To these, I would clamp the laser detector such that the detector was directly above the outside edge of the footing. With the laser placed directly above my reference corner, I rotated the laser until it shot directly to one of the adjacent corners. Now the laser was set.
I then walked to the other adjacent corner and moved the corner form until the laser detector found the laser at the outside edge of the form. In the picture below, the pencil line indicates the outside edge of the form.
This means that the corner the laser is placed at is now square with these other two corners.
I moved the laser to the opposite corner, and rotated it until it intersected the first adjacent corner. Same as before, the laser is now set. I took the laser detector down to the other adjacent corner and checked where I was.
Off by about 1.5 inches. Thats actually not bad. All my length measures were perfect. Being off by 1.5 inches on this corner will be worked out once we are standing up the walls. In this particular area, the footings are 12” bigger than they need to be anyway (the footing can get much skinnier in this area, but I’ve left it full size for ease of setting up the forms), so I have a lot of wiggle room. This is where we wanted to be by end of day Saturday. Now to try and make up for lost time.
Now I have to get everything level. This is another spot where we made mistakes last time. In the process of getting the forms level, they were accidentally moved one way or the other an inch or so, falling out of square. This time I drove a couple steel stakes into the ground around the corner, semi-securing its position while I lifted the form up off the ground to level.
I should mention that our forms float off the ground about 3 inches. I am using 2x10’s for our forms, which are only 9.25” wide. My footings are 12” thick, so these will float approximately 3” off the ground. I can’t hold these off the ground, get them level and screw them to a stake all by myself though.
I brought up some shims and used scrap wood to get them at the right height, and checked my level with the laser. This was more precise than we were able to do on Saturday since one of us wasn’t trying to hold a board level. I could fine tune the height with the shim, check and recheck, before driving any screws into it. Things moved slowly though. By the end of the day, I had half of one side of the forms done.
The day was also interrupted by a few visitors. The folks from the concrete company stopped by and confirmed they would back down our driveway (I would have placed the odds at less than 50⁄50) as long as we have someone spotting them. Yakima Co-op Propane stopped by and approved where we want to bury the propane tank. We talked through a few logistics. I am hoping we can get the tank in by the end of summer.
Lastly, a shipment of rebar arrived. Its all the rebar we should need for the footings, or about 4,000 pounds worth. It didn’t look like much until I started to help unload. We are using #5 bar, which is thicker than usual, and its grade 60, which is denser than usual too. This stuff is heavy, and its bundled in sets of 10 pieces. The good news is that most all of our bends were done at the yard, so I should save some labor there. We’re just dumping it off the side of the truck. I will have to figure out how to move it down the basement tomorrow.
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