Old 10-12-2006, 06:33 AM
jengineer's Avatar
Master Builder
Join Date: Aug 2005
Location: Garden-A, South California
Posts: 572

SonoTube is a name brand of a very stiff carboard like tube. do a ggogle search. They are used as concrete forms in the construction business. In the good old days you would either auger or take a PHD (Post Hole Digger)and make your hole in the gorund and then fill it up with concrete and rebar. If the design called for a 10 inch hole you would dig a hole with a minimum of 10 inches and then fill it up. In places where the soil is not compactyed you run into the problem of the walls collapsing before you can get the hole filled with concrete. As material is $$ especially in big projects it pays to use sonotubes to make a precise sized pillar of conrete and then back fill.
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Old 10-12-2006, 11:15 PM
carioca's Avatar
Join Date: Sep 2006
Location: Charlotte Bay, Australia
Posts: 264
Default post-hole digger

Thanks, jengineer! as an old hobby farmer I've got just the right size post-hole digger on hand so I can save the expense of the sonotubes (you're too right, I should have googled first!)...

Now all I need is a structural engineer who'll volunteer a recommendation re the depth of the piles :-)


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Old 10-13-2006, 06:01 AM
CanuckJim's Avatar
Il Pizzaiolo
Join Date: Jan 2006
Location: Prince Albert, Ontario, Canada
Posts: 1,480
Default Tube Depth


The depth of the tubes really depends on soil conditions, and frost, if any. Here, code for footings, pole barn supports, fence posts, etc., is four feet, because of frost heave. Supposedly, that depth will get you below any frost line, but this just isn't always so. You really have to determine the stability of your substrate, in your case, clay. Do you have any ground water to contend with? As a rule of thumb, I'd go down about three feet into the clay if you have no frost and no ground water, say from a spring, running between the topsoil and the clay. This is exactly the problem I had to solve, plus frost, hence the necessity of building thick and drilling deep. The part of my land on which the oven sits actually moves from frost, visibly, because it sits, essentially, on an underground stream.

Versachi, thanks for the frost link; very interesting and helpful. I think you understand what I was up against and why I built the way I did. Last winter wasn't all that cold here, but very little snow, so frost was about two feet. Thus far, I've had no cracking whatsoever, either in the slab or the oven. This winter, if the seed production on the cedars and maples means anything, is likely to be a lot colder. Time will definitely tell. First snow shower yesterday, which is early for around here, but not for Buffalo or Thunder Bay.

Slab construction has to be one of the cheaper parts of this kind of oven building, so, to my mind, it's better to go heavy and safe than thin and, umm, head scratching. Like Versachi, I would definitely recommend excavating top layers until a stable substrate is reached. The clay here is yellow, and digging in it is like cutting hard cheese. In the old days, they made yellow bricks out of it, called marls, and that is one of the reasons I chose yellow brick for the facade of my oven. Check out www.marygbread.com to have a look.

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Old 10-19-2006, 06:27 PM
Join Date: Oct 2006
Location: Adelaide, Australia
Posts: 257
Default Pier Depth


My soil is a very reactive clay called 'black earth'. The engineer's report for the last extensions I did called for 900mm deep x 380mm wide footing with 6 x C16 bars (3 top 3 bottom) with W6.3 ligatures every 900mm. These were for external footings. Internals were still 900mm deep, but 300mm wide and 4 bars instead of 6.

I plan to go down 900mm for the perimeter footing of my oven base. As I'm going to have an adjoining brick work bench, barbecue, sink etc with 2400mm high double brick wall behind it to form one side of the pergola, I'll be continuing with the deep footings to be on the safe side!

Last edited by Hendo; 10-20-2006 at 05:45 PM.
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Old 10-24-2006, 01:35 AM
carioca's Avatar
Join Date: Sep 2006
Location: Charlotte Bay, Australia
Posts: 264
Default Muito obrigado!

Many thanks, Hendo, that gives me something to work on. Am about to order the bricks for a 1.2 m dome oven, minus all the mortar and vermiculite etc because I can get that from a Sydney supplier as and when I need it.

(just wanted to have the cut bricks on hand for a 'dry run' while I work on the foundation...)

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