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Will a sonotube rot underground?
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Lynn Kasdorf - Leesburg,    Posted 07-30-2003 at 08:31:15       [Reply]  [Send Email]
So I'm building this big ol' pole building, and attempting to drill suitable holes for the 6x6x16 PT poles I'm using.

The old Danuser auger on my Ford tractor just doesn't go quite deep enough. I want the poles to be 4' in the ground. And when you pull the auger out, a bunch of spoil falls back into the hole that you have to remove by hand. The soil is damp and sticks to the post hole digger, making the process tedious. I have 2 poles in the ground and 8 to go.

So I get to thinking- I have a full size backhoe that is just sitting there and itching to dig some holes...why not dig a pit the the right depth with the backhoe, and place a 12" x 4' or 14" x 4' sonotube at exactly the right position, and backfill around it? Then I'll drive some lags into the pole, paint the section to be buried with tar, and place into the sonotube.

I'll fill the sonotube with concrete and crown the top for runoff. I'll grade to the top of the sonotubes, then put down gravel.

The only question I have about this is whether sonotubes are rated for spending their life underground. They are basically carboard, treated with wax or plastic or something. Will they eventually deteriorate, leaving a gap around the concrete post? Seems unlikely to me...

I guess the downside is the cost of the sonotubes. Concrete is cheap. Time is not, and this approach should be faster than augering and digging holes.


Debbie    Posted 06-15-2007 at 12:51:36       [Reply]  [Send Email]
I am currently in the process of building a home with the sonotubes and wanted to know if you think that is a good idea. Sonotubes outside covering is suppose to be (according to manufacturers instructions) be removed 5 days after the concrete has been poured. They are not designed to stay on indefinately. It is just the form. We are going to have our soil tested before we pour the tubes to see if there will be any problems with the ground shifting. We also are hiring a engineer to tell us exactly where each tube should be. We were told that they need to be buried 2-3 ft under the frost layer. We have chosen the sonotubes because our property has a natural slope that will cost a lot to fill in. Thank you for your comments.

Jimbob    Posted 07-30-2003 at 19:47:12       [Reply]  [No Email]
Sonic tubes will eventually rot away. Just caulk the area when it goes. No big deal. In fact, on commercial buildings, it is called an isolator. The best construction uses isolated the piers.

buck    Posted 07-30-2003 at 19:13:08       [Reply]  [No Email]

I'm going to side with Toolman here. You have already desided that the 6x6 pole has enough baring to hold up the building and that 4' is your desired depth so just dig the hole with backhoe,brace pole at desired location and backfill with compacted native material.

RayP(MI)    Posted 07-30-2003 at 17:33:47       [Reply]  [No Email]
Well, what not to do: DO NOT rent one of those "two man" augers. Those'll kill a couple of guys, unless they're in real good shape and really big guys! Picking them up above 4' and the digging clear to the 4' depth isn't easy. I used an auger on the back of the tractor, as yours. Cleaned up the holes with a conventional double shovel hand post hole digger - and then used a shop-vac to clean up what I couldn't do with the posthole digger.

In this area, the latest recommendation is the same 4'depth, and placed in the bottom of the hole, a 12" concrete "cookie" which the post rests on. Theory is that this will probvde drainage around the post. Any necklace or boot of concrete will hold water against the post, and promote rotting. I went one step further and backfilled all holes with sandy gravel, to promote draining. Around the base of the building, I placed a "skirt" of heavy plastic sloped downward away from the building, to promore drainage away from the walls and poles. Covered this with a few inches of dirt.

Charles(Mo)    Posted 07-30-2003 at 16:07:16       [Reply]  [No Email]
Just a thought. You can contact your electric provider and ask if they would come out and dig the holes for you. We do this occasionally and only charge $35. hour. If it isn't solid rock, I could dig them in less than a half hour. I work for the electric coop, and we try to help our members out.


Hal/WA    Posted 07-30-2003 at 15:35:38       [Reply]  [No Email]
What does your building code say about concrete around poles? In my area it is required, but just across the state line in Idaho, it is not. A friend of mine has built about 150 buildings in the 2 states, and his recommendation is to not use any concrete if the building codes people will let you get by without it. He says that the good pressure treated 6x6 poles actually last a lot longer in decently drained soil than they do trapped in concrete. The only real good reason I can see for using concrete around the poles is if you need the anchoring weight because your location is subject to very high winds and you are putting the poles at maximum distances apart. Concrete costs money, as do sonotubes or whatever you use for forms. I think I would rather use concrete money to pour a nice floor.

By the way, I think that 12" diameter concrete around the poles is less than the code requires in my county. I can't find the brochure, but it seems like they require 2 feet. I suppose there are sonotubes that big, but I used barrels with the ends cut out for pole forms in a pole building I built. They were free, although it took about 15 minutes to take the ends out of each barrel with the air chisel.

Good luck with your building. You might want to talk with others that have built pole buildings in your area and see what they did, and why they did it that way.

Chuck, WA    Posted 07-30-2003 at 15:49:39       [Reply]  [No Email]
I'm also in WA, but not in Hal's area. My county code requires 2 ft. diameter x 4 ft deep holes, 4" concrete pads at the bottom, then natural fill. Some folks fill with gravel, some concrete, and some with dirt. My soil is clay once I get below the topsoil, so I just water settled the dirt back into the holes. Poles are 6x6, 4x6 and 4x4 depending on location. Barn is 24 x 36, 12 ft eaves with a gambrel roof to a 21 ft peak, with a 12 x 36 shed along one side.

We get a lot of wind in the spring and late fall - had some gusty winds to around 80 mph. Barn stands firm!

I rented a Bobcat with 24" x 4 ft auger instead of fighting with my 12' x 3 ft 3-pt auger and having to hand dig the rest. Dug 17 holes in a couple of hours. Wouldn't hesitate to do it that way again ... not worth the extra work for what it cost.

TimV    Posted 07-30-2003 at 09:31:32       [Reply]  [No Email]
Lynn: Yes, they will rot, but as they are very thin, it won't leave an appreciable hole around the post. However, I'd be VERY careful about doing what you're planning on--the wood will rot from contact with the chemicals in the concrete. A better way is to pour your tubes full, then put the poles on top with a pole standoff--they're set up to give you a 1" gap between the pole and the concrete, which will help minimize the rotting problem. You can either put a "L" bolt into the concrete while wet to secure the base, or Tap-Con the base to the concrete and set the pole on top of that.

Lynn Kasdorf - Leesburg,    Posted 07-30-2003 at 11:30:53       [Reply]  [Send Email]
I found this, and it makes sense to me:
"It is not a problem for pressure treated lumber to contact concrete, the mudsills of nearly every house built is of p.t.
The problem you want to avoid is encasing the bottom of the post in concrete, water will soak into the post and get trapped in the bottom of the post, rotting it faster.
We like to use 6" of gravel in the bottom for drainage, then concrete. Also if you extend the concrete up a little from the soil, you will avoid standing water at the base of the post, another problem area."

Regarding attaching the post to a concrete pier with an anchor, I think that defeats one of the big benefits of a pole barn- the stiffness of the poles in the ground. A pole sitting on a metal anchor would be a hinge point.

All the pole barn books suggest a concrete necklace at the bottom of the pole. I am thoroughly covering the part of the pole to be embedded with thick roofing tar, especially on the end grain, so I figure that this shoudl minimize the wicking of water. The bottom of the poles won't be in cement- they will sit on gravel.

I imagine almost any way I do it will last plenty long, including just a dry backfill and tamping, but I want to over-build it :)

TimV    Posted 07-30-2003 at 12:37:35       [Reply]  [No Email]
Lynn: The part about putting the bottom in concrete is certainly correct, however, I've also seen problems with encasing the entire post in concrete--it's not recommended due to concerns about rotting. Putting a coating of tar on the posts MAY help, though I've seen no data to support it (or any at all that showed tar on the posts). You may want to check your local building codes, if you're going the "legal" route with a permit,inspections, etc. As far as stiffness concerns, if your structure is properly designed and braced, there should be more than adquate stiffness inherent in a design with standoffs.

Um...    Posted 07-30-2003 at 08:57:13       [Reply]  [No Email]
That is exactly what SonoTubes are for...

They are just a form for the conrcete and then they disintigrate after time...

Go forward with your plan and never look back...


toolman    Posted 07-30-2003 at 08:55:48       [Reply]  [No Email]
i don,t think it would matter if they did and im sure they will ,however whenever i have poured concert around poles be it presure or not the poles will rot off quicker and usually right at the top of the concert, id just dig the holes with the backhoe and sit the poles in with the hoe and back fill with dirt ,if the dirt has more gravel or is rocky the better drainage,tamp it tight with the hoe and you can even move it around to straighten with the hoe , thats what we did here when we built ours 20x40x16 14 years ago now.good luck

markct    Posted 07-30-2003 at 08:38:30       [Reply]  [No Email]
well they seem to last a long time from what i have seen, but who cares if they dont, they are just a form for the concrete basicly, the concrete is the structural element there, the tube just holds it till it hardens.

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