Going to be putting up a cold storage building this summer. Steel building, 80 x 250. There will be 25 piers connected by a 2' by 2' concrete grade beam. The piers will be 5' by 5', and will set 18" lower than the grade beam. What our concrete guy is wondering is since he doesn't use 2' forms for pretty much anything, and lumber has gone so crazy in price (it would cost close to $15k for the lumber to build enough forms), is it acceptable to use the earth for forms? We haven't fully figured out if it's even possible, because with our freeze/thaw cycles we can't have the top wider than the bottom, which is what would happen if you dug a 2' wide trench and set a 2x4 form a couple inches back from the edge to have solid ground to stake to. Anyone have any ideas on how to pour this 2' by 2' grade beam without using over 1300' of 2' forms?
Given the size of the project, why doesn't he rent the forms? I know 2 places locally that I could rent 2, 4 and 8 ft concrete forms from locally. Also, could he split the pours, thereby needing less forming material? We just poured 300 ft of curb in one of our dairy barns and split the pour up into 4 separate pours due to form materials cost.
I would look into splitting the pours, do the footings then the grade beams. Use the soil on the 2nd pour for the 2x2 except where it crosses a 5x5 footing.
Dad, then I, have poured thousands of feet of foundation walls cut with a chain trencher. As far as a neat edge, I have nailed legs to 2 x 4 and 2 x 6 that extended away from the trench at a 90 degree angle to allow the form to be staked away from the trench.
Here we dig all our grade beams into the ground no formwork required and if you know how to shave out a ditch the edges are clean trenchers do the same with great effect with good operators
What do you use for a grade board to screed the mud?
Typically top of footing is 6 inches to a foot into sub grade so you set a grade nail into the ditch at top of footing paint it so you can see it when you poor space those about every 10 to 12 foot While you poor you can use a 3 foot long board with a handle screwed on and you can hardly Darby the footing even if you need a smooth top get a trowel and swipe it 2 or 3 times Here finish floor is typically a foot or 10 inches above top of footing so use forms to pour the slab as a turndown and your in buissness
So, this is a cold storage. There are no footings, and will be no floor. This 2 x 2 grade beam is what the walls will match up with to seal the building, and I believe the builder wants the entire thing poured as one.
How much of the 2x2 grade beam will be above grade? Can you pour the 5x5 piers first and then come across with the grade beam? If you can pour the 5x5's first then you can cut the trench for the 2x2 grade beam. Dig the grade beam slightly wider and hang the form over the trench so the top is not wider than the bottom. Get some 48" steel drive pins to anchor the top form (the clean edge) that you can remove as the concrete hardens but before it sets. Kick it off with 2x4 triangle braces with holes drilled in the end with drive pins to anchor to the earth. This method requires stripping the forms while the concrete is still green so care has to be taken working around the finished edge. Homebuilders here use a similar technique for slab on grade houses. 24" wide footing where they hang a 2x10 6" in from the outside trench edge in order to form a brick ledge. The 2x10 forms a clean edge and the footing pours out under for a brick ledge. They use 2x4s to secure the clean edge form into the footing and remove the 2x4's before the concrete fully cures then fill the holes in with concrete. This method still requires wood but less than building that many 2x2 forms for both sides of the grade beam.
Many times I have driven rebar vertically into an excavation (ditches) and then set a straight 10'- 2x4 on them. I drill holes half way through the 2x4 for the rebar. I use a laser to set grade as I pound the 2x4 down the last couple of inches. Usually 3 rebar for each 2x4. Pour 10 feet, pop the 2x4 off the rebar and fill the gap with a shovel. If the ditch has no forms and is very far below the surrounding grade I use rebar with a hook bent on it to pull the 2x4. I use the same method if a slab is over 12 feet wide.