I'm building a largish deck this summer, which will be attached to the home via ledger. The plans call for 14 pier footers, each 2' in diameter, 4' deep. I had planned on placing Sonotube forms into each of the holes.
Over the weekend I dug the holes with the help of a skidsteer, and I'm now wondering if the extra expense of the forms is necessary. The ground in our area is hard clay, and I'm looking at 12 almost perfect cylindrical voids in the ground (two had some problems...haha).
The primary advantage i see of the concrete form is getting the pier above grade, but at $40+ per hole for the 2' tubing, I'd rather spend the money on a new table saw.
I will be using rebar either way, just looking for some feedback.
Since you went so deep, you must have a deep frost. I suggest gravel at the bottom and as back fill. This prevents frost heave as you especially need with such deep footings. Also, I would pour the footing pad (recommended to prevent heave) separate with steel to connect to sono pour later. Then wrap plastic around sono before install to help prevent heave. The water freezes around the pier forms ice lenses (Google that) and displaces or jacks the pier. As it freezes around, it also freezes under, even beneath the frost line. Even the manufacturer of tubes recommend gravel.