Are sono tubes absolutely necessary for deck footings?

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Old 12-12-14, 06:08 PM
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Are sono tubes absolutely necessary for deck footings?

My local building code doesn't state anything about forms or tubes. The deck has already been built but I was just curious. The footings were placed with around 1-2 feet long sono tubes from 6" above grade. So basically the tube is only placed from the top to just about half way down the pier. I've read mixed opinions about this topic. Hoping to get a final conclusion, not that it will change anything since the deck has already been built but for future reference.

Best point I read was that without a sono tube, the concrete can fill in the imperfections and wedge into the soil. While with the tube it's a concrete pier that is practically "floating" in soil.
 
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Old 12-12-14, 06:55 PM
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AFAIK, Canadian code requires 4' footings & I would use sono tubes that go the distance. The above grade portion should be sloped so that water doesn't collect where the post meets the base.
 
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Old 12-12-14, 07:12 PM
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Yep I've gone 4.5 feet down. You say "I would". Any particular reason for this?
 
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Old 12-12-14, 08:08 PM
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The tubes help maintain the strength of the footing. There is less chance of the sides blowing out, from the weight. I once had to build a deck where there was a high water table. I wrapped the bottom of the tube with heavy plastic & that prevented the concrete from disappearing, into the ground.
 
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Old 12-13-14, 05:00 PM
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The tubes provide absolutely no strength to the finished pier! You obviously need them above grade to make the visible part of the pier look good. I've never seen a code that requires them below grade.

There are two schools of thought about using them below grade. The first school which I'm part of says that you are better off not using them unless the soil in your area collapses back into the hole like it would in sandy soils. This way the concrete fills the entire hole, you don't need backfill which is hard to compact to support the pier. The other school says that you need to was all the way down so that the pier doesn't move if the soil moves during freezing and thawing cycles because the sides are smooth.

There's no right or wrong way of doing it, it's all just personal opinion or who you believe is telling you the correct information.I have never seen the sides blowout during a pour like the previous poster mentioned. I suppose it would be possible under the right conditions but those conditions are extremely rare.
 
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Old 12-13-14, 05:42 PM
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That's what I was wondering also because I just finished a concrete course and it was never mentioned that the tubes increase any strength.
 
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Old 12-13-14, 07:15 PM
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Contrary to a previous poster's claim, I've seen more than one instance of sonotubes blowing out from high fluid concrete forces acting against the inside of the tubes. Granted, the blow-outs occurred very close to the bottom of deep forms, probably greater than 18' or 20'. Experienced contractors don't normally use sonotubes for anything deeper than 15' or so, but rather rely on bolted and pinned steel column forms. Even they can blow out, with most contractors making a practice of delaying their columns' concrete placements to allow the bottom concrete to take an initial set before adding more weight of fluid concrete on top of them.
 
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Old 12-13-14, 08:11 PM
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Bridgeman, obviously any product can fail if used incorrectly! However I've seen sonotubes 30' tall above grade used without any problems of blowout by relatively inexperienced contractors! Under normal conditions and used correctly blowouts using them are unheard of!
 
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Old 12-14-14, 05:30 AM
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Additionally, the location of the site will dictate whether single footings are allowed or not. For instance, here in the mountains, we cannot use single footings for decks within 20' of a drop off. We are required to pour continuous footings at or below frost depth. I have seen decks literally sink on the edge of a precipice that gave way to single footings. There is no lateral support as a continuous footing would provide.

As far as using sonotubes, as mentioned, soil conditions will dictate, as well as $, since you will obviously be pouring more concrete to achieve the same vertical strength.
 
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Old 12-14-14, 02:56 PM
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Under normal conditions and used correctly blowouts using them are unheard of!
Great quote, faulty logic, but you could use that quote for every product every made.

Sonotubes have zero structural value. We are talking about a deck or garage piers, not large structures. So the crazy 20-30' piers aren't applicable.

We never install a sonotube to full depth unless soil conditions are terrible. In fact I usually only install the top 1-2' for a typical pier. If I have to install close to full length, I bell the bottom of the hole out about 4" wider than the sonotube. This allows the concrete bell at the bottom to act like a cork to prevent water or frost from slowly pushing the pier up.
 
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Old 12-16-14, 08:40 AM
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In cold climates that experience freeze/thaw cycles it's long been recommended to do as Hellrazor suggests. I've seen a trick to tape a large garbage bag to the bottom of the tube and raise it off the floor of the hole--which is hand-dug out larger than the bore. The bag expands with the concrete to make the large-base "plug" that can't be pushed up as ground moisture freezes and expands. There are manufacturers that have responded to this method by producing funnel-shaped forms--but I image they require a full-diameter bore just to get in the hole, then back-filling.
 
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Old 12-16-14, 12:20 PM
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The funnel-shaped forms are known as elephants' paws. They're usually made of heavy black plastic, and have adjustable narrow ends that are cut in the field to match the size of the sonotubes. A common mistake of inexperienced contractors is to install them without cutting off the narrow ends (such that they just fit inside of the ends of the sonotubes), resulting in compromised footings. The last ones I looked at in Colorado a few years ago were at the bottoms of 12" sonotubes, with the uncut funnel ends looked to be only 6" in diameter.

An advantage of (correctly) using them is that the spaces between the sonotubes and earth around them can be backfilled with well-draining, washed rock or pea gravel. Unlike saturated soil, the rock isn't likely to expand as a mass when it freezes, resulting in minimal uplift pressures on the walls of the concrete footings.
 
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Old 12-17-14, 02:07 AM
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did you just make that ' elephant paw ' thing up, bdge ? good post - thanks for the education
 
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Old 12-17-14, 03:57 AM
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Nope, the elephant paws are used quite a bit in northern climes such as Massachusetts. We don't have a call for them here in the south. I'd rather pour a continuous footing than to dig several crypt size holes for the paws. Hole auger for sonotubes or back hoe for the paws. Just a preference, though.
 
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Old 12-17-14, 12:19 PM
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When aiming to apply veneer stone to a finish footing (rectangle or square) are people mainly constructing their one forms or are there manufactured forms for this as well?
 
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Old 12-17-14, 04:18 PM
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Absolutely no idea what you are talking about. Footings are normally not veneered. Clarify your question a little.
 
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Old 12-17-14, 05:11 PM
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The biggest advantages of a Sonotube:

1) It used a predictable amount minal amount of concrete.
2) The diameter size and/or foot measurements can be varied. Obviously, a bored or very clean hole with a post hole digger up to 4' or 5' is very doable, especially with solid or cohesive soils and less material is involved (excavation, or backfill).
3) The Sonotube provides a clean surface than can even be exposed by peeling off the cover.
4) is allows filling with the proper procedures even if the hole is full of water. - Let the concrete go to the bottom slowly and push the water up and ou - same as pouring bridge foundations/seals underwater.
5) The biggest advantage is that the frost does not adhere to the Sonotube. When you think about it, the ground freezes and forms ice lenses that causes heaving as it proceeds freezing downward. If you have a dug footing that is an upside down cone (wider at the top), the heaving begins much before the theoretical frost level. In other words, the upper soil is what causes much of the heaving. The Sonotube carries the vertical load down to the bearing base and the expanding soil above can heave and just slips upward. A rough sided hole gives the frozen soil a surface to bond o the concrete and pull the concrete up since it is bonded to the soil. Back filling the gap between the Sonotube and the native soil with granular material (sand and rock) also helps to prevent the upward pull.

Dick
 
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Old 12-18-14, 06:19 AM
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or are these considered more of a pier?
 
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Old 12-18-14, 03:11 PM
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These are not footings, but piers, and can be primarily of 6x6 lumber set on footings to support the decks. The rock is either built up and applied to a false framing or mortared in place with proper preparation around the support member. The rock are not supportive of the deck.
 
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