Formwork you throw away, not a foundation system
The name gets used the way people say Sheetrock or Bobcat. Sonotube is one manufacturer's product and the generic thing is a round fiber form: heavy spiral wound cardboard, waxed on the inside so wet concrete does not soak in and grab hold. It comes in a range of diameters and gets cut to whatever length the hole needs. It is formwork with a single use in it.
All it does is hold the shape while the concrete is soft. Once the pier has set, the tube has no job left. That is worth saying out loud, because people sometimes talk about a Sonotube as though ordering one settles the foundation question. It does not settle anything. The pier is only as good as the dirt under it and the steel in it, and both of those come off the plan.
Round pier, or a footer running the whole wall line
A pier is a point. A footing is a line. That is the actual fork, and it decides which one your job gets. A deck, a porch, a set of columns carrying a beam, a post frame building: those are point loads with open air between them, and a round pier under each one is the sensible answer. A house, an addition, a garage with a stick built wall standing on the concrete: that load runs continuously along the wall line and wants a continuous footing under it.
Neither one is a step up from the other. Piers under something that needs a wall leave the runs between them carrying nothing. A full footing under a deck is concrete nobody needed. On most jobs the drawings have already settled it before we get a call. Where it is genuinely open, it comes down to what is being carried and whether the space underneath is meant to be closed in later.
- Point loads standing alone, deck posts, porch columns, beam supports: round piers in tubes
- A wall bearing continuously on the concrete: a footing running under the whole line
- A post frame building: posts on their own footings, with the floor slab poured as separate work
- A hole in wet clay that will not hold a clean edge: a tube, because the dirt will not form it for you
The hole under the tube is the part that decides everything
Whatever the pier does, it does through the dirt at the bottom of the hole. So that bottom has to be firm undisturbed ground, cleaned out, not the loose spoil that slid back in while somebody went to get the tube. Dig four holes on a lot around here and you will usually find red clay sitting on rock, with the rock closer to daylight than anybody planned for.
The bottom of the pier also has to reach past whatever depth the ground freezes to, for the same reason a footing does. Water in the soil swells as it freezes and lifts whatever is sitting on it. That is frost heave, and a short pier with a light building on it is easy to lift. The depth that applies is a code question tied to your address and your elevation rather than a figure to read off the internet, and we confirm it on your written estimate before anything gets dug. Work that holds a structure up also needs a permit and a footing inspection before concrete goes in, so the hole gets looked at while it is still open.
Then plumb and bracing. A tube that leans, floats up, or gets shoved sideways when the concrete hits it sets that way for good. Steel, where the plan calls for it, is tied and held out in the middle of the tube instead of leaning on the cardboard. Post bases and straps go in while the concrete is still plastic, on the layout your framer is going to build to.
Four piers on a Saturday, against a long row of them up a bank
If you are setting four piers under a small deck, you do not need us for the concrete. Bagged mix, a wheelbarrow and a level will do it, and plenty of people around here have done exactly that. Call the county about the permit and the inspection, dig the holes right, and the rest of it is patience.
What changes the answer is the count, the access, and what else is pouring that day. A long row of piers under a barn, a porch or a pavilion adds up to real yardage, and yardage means ready mix instead of bags. Ready mix comes in ten cubic yard loads, and we order about ten percent over the calculated volume so nobody comes up short at the last hole.
Then there is where the holes sit. Piers get dug on the side of the building with no room, up a bank, or behind a gate, and a loaded ready mix truck cannot get near them. That is the trigger for the pump. Ours is a trailer mounted line pump on 2.5 inch and 3 inch line, worked by our operator and a hose hand, so the truck stays on ground that will hold it and the hose comes to the tube. When another contractor is setting the piers and only needs the concrete placed, that part is ours: we bring the pump and the two men and put the mix where you want it.