Explain concrete sonotubes to me

marchanna · Apr 25, 2018

npalen said:
Read thru the posts fairly fast but didn't notice that anyone mentioned what happens if/when the tube itself deteriorates. Not proclaiming a problem with that but just something that probably happens over time.

The tube always deteriorates. Usually only after a couple years. It’s a gradual process and the soil just settles in as it happens. Is a non-issue because the tube is so thin.

/pine · Apr 25, 2018

FWIW...If the top of the piers are larger than whatever is bearing on them...the top of the pier should be slightly canted away from the bearing points to prevent water from laying on top of the pier...

MossRoad · Apr 25, 2018

They also make a finish-free type product that has no lines inside, and a zip cord built into the tube. After the concrete cures, you pull the zip cord and it rips a slit for you. Then remove the tube. No manual cutting required and it leaves a smooth finish VS the more traditional spiral pattern that's seen in the concrete after the regular sonotubes are removed.

MossRoad · Apr 25, 2018

/pine said:
FWIW...If the top of the piers are larger than whatever is bearing on them...the top of the pier should be slightly canted away from the bearing points to prevent water from laying on top of the pier...

Yep. Try and smooth a little raised crown to the top of the concrete so any water wil run off and not puddle.

MossRoad · Apr 25, 2018

The tube will rot away. They can be removed, if desired, by making a slit on two sides, then around at the depth you want to remove it, then peel it off. It's waxy coated inside for easy removal.

MossRoad · Apr 25, 2018

And they make great forms for cat climber/scratching posts, too...

He's so cute!

AHHH, My finger!!!

That's better.

Rustyiron · Apr 25, 2018

bdog said:
This is exactly what I was try to say is the problem I see with putting the tube all the way in. If you dig a hole and put a post in it and fill with dirt it will never be stable. However if you drive the post in which many people are doing here now it seems to work fine.

I took your OP as you wanted to use sonotubes. Sounds like you just need to drill a hole, fill it to a few inches below grade then simply use short pieces of the tube to your desired height above grade, simply as a concrete form for the exposed portion. quick & easy.:thumbsup:

joeu235 · Apr 25, 2018

The diameter of the pier has more to do with the weight bearing capacity of the soil than the strength of the concrete.

TractorNH · Apr 25, 2018

In some jurisdictions where the ground is prone to frost, there is also a requirement in the building code where the tubes need to be installed and inspected before the concrete is placed so the inspector can verify the depth of the tube is below the frost line. You can't do that any other way than by using a tube of some sort that can be backfilled after it's installed.

oosik · Apr 25, 2018

View attachment 550747 View attachment 550748 These pictures were taken to show the first row of logs on the cabin we built in AK. If you sort of use your imagination - you can see the sonotubes on this end.

bdog · Apr 25, 2018

Rustyiron said:
I took your OP as you wanted to use sonotubes. Sounds like you just need to drill a hole, fill it to a few inches below grade then simply use short pieces of the tube to your desired height above grade, simply as a concrete form for the exposed portion. quick & easy.:thumbsup:

Exactly. I am making a 3 sided implement shed. A fairly large one 90-100' long. Wind uplift is a concern. I plan on embedding weld plates in the concrete to attach my columns to so that I can more precisely place them. I plan on using my GPS to mark all the column locations and it is much easier to place a weld plate in the correct spot than to try and get a 10' tall post in the right spot. They don't need to be very high but I want the weld plate/column joint to be above grade slightly as the columns they specified for me are rather thin and rust through is a concern.

Rustyiron · Apr 26, 2018

Little idea here bdog,
If you want a "skirt board" down AT grade to keep the wind, critters, etc. out of the bottom of your wall, and that's where your concrete "tube's" are, you might cast in a pt 2x4x? inside (vertically) your tube form @ grade for something to nail your skirt board/siding to. I've done similar screwing through the form from the outside, into your 2x4 block. On the concrete side of the 2x4 block, drive some nails or lags so it's better attached to the 'crete.
Little details like this add up to an easier job throughout the build.

chim · Apr 26, 2018

bdog said:
This is exactly what I was try to say is the problem I see with putting the tube all the way in. If you dig a hole and put a post in it and fill with dirt it will never be stable. However if you drive the post in which many people are doing here now it seems to work fine.

As a side note, it's all in the compaction, and that means having enough clearance between the concrete and the side of the hole. We've been installing site lighting since the early 70's. Back then everything we did was cast in place. Some specs called for square bases back then. Now they are almost exclusively round.

For a couple decades we've been pouring round light bases at our shop for field installation. The bases all have rebar cages and conduits cast in them. The poles range from the short bollards seen along walkways to 40' poles for parking lots. We've installed hundreds and never had a problem. The largest bases I recall were 24" diameter and 9 feet in height for a project about 4 years ago. There were 135 of them on the project.

We used Sonotube for a while, and it was expensive. We then switched to fiberglass forms about 15 years ago, but they were difficult to keep round. For the past 10 or so years we've been using plastic forms that are very rigid. Earlier this week we pored some that are 24" in diameter and 7-1//2'' tall. We do this in the one end of the Weld Shop and use the overhead cranes to load them onto our flatbed trailer.

PILOON · Apr 26, 2018

The smooth surface of the tube is less likely to be grabbed and lifted by surface frost action.

Also generally installers slit the last foot or so to create a foot by splaying the tube about 50% wider.
Especially good in softer soils for load bearing and in frost areas the wide foot deters frost heave as it then acts like an anchor.

Some suppliers offer a plastic 'slip on' foot usually creating a nice mushroom like base.

Generally about a month or so later the tube is so wet/soggy that the above ground section is easily peeled away, LOL, more like un winding.

Tomtint · Apr 26, 2018

We use them up here on a regular basis. I like to fill the 4' hole up to about 12" below grade then put a piece of tube on the top of it just high enough above grade, where we want it. The extra concrete usage is worth it to me instead of trying to pack soil around a tube and having it move around.

forgeblast · Apr 26, 2018

I saw these mentioned on a different forum as an alternative.
Helical Piles - Screw Pile Foundations - Techno Metal Post

Snobdds · Apr 26, 2018

Here is how an engineered sonotube foundation is made. The snotube is not in the ground, the base foundation box is. The sonotube is held up in the box (see fist pic) with rebar and then a monolithic pour is made.

Now we put the entire cabin foundation on top of an old glacial till area, so there was no need to go down below frost level as the big open rocks had no hydraulic pressure action on the boxes. The boxes only go in the ground about 10 inches, per design. The boxes are what hold all the weight, the sonotube piers just make a level platform for framing....