Round foundation help

[Neil2]

Re: Round foundation help

When using sonotube as a form make sure it is well braced bottom and top. At the bottom, a triangle of 2x4 should do and weight them down well.

Vibrate or tamp the concrete and once the form is full lightly tap the sides of the tube with the handle of a hammer. This will ensure a smooth finish to the exposed outside. You can tell how hard to tap it by looking at the top edge when tapping near the top - the wet concrete should be just "recoiling" slightly from the form. Don't worry about this too much, if there are any voids or holes they can be filled or parged later.

Leave the tube on for at least 7 days and keep damp the whole time.

[tony boca]

Re: Round foundation help

Neil,

If I go with 4 sonotubes, will the 60% rule apply to an 80" diameter also. I'm concerned that three may not be enough for this size.

I was also thinking of instead of using a wooden frame to support the plywood, what if i used stacked concrete blocks(which i now have many) and a piece of 2x4 between the block and the plywood. After the cement dries, i knock out the 2x4 and the plywood should come apart easily?

[Neil2]

Re: Round foundation help

Tony

When I first started designing my oven, I toyed with the idea of using just one 12 inch pier.

With 4 still use the 60% from center of oven to center of pier dimension.

The blocks to support your form should work OK. If you can work it so you have some narrow wedges between the block and the 2x4s (or between the 2x4 and the plywood) you will find it easier to dismantle once the concrete suspended slab has set.

[tony boca]

Re: Round foundation help

I have a concern about bonding the piers to the foundation. Should i wet my cement foundation before filling in the sonotubes? Or will the piers bond better to a dry foundation?

[Neil2]

Re: Round foundation help

Wet the foundation - really soak it. You should also have a mechanical bond. Can you drill into the foundation and grout in the rebar ?.

Correction to one of my earlier posts in this thread, I used 3/8 inch rebar (not 1/2 inch). If you can get the 1/4 inch rebar locally this would work as well and be easier to bend.

[tony boca]

Re: Round foundation help

Thanks Neil
I drilled 3/4 holes into the foundation,filled them with concrete epoxy, and placed three 1/2" rebar. Used four 8" sonotubes. Filed them with cement and now waiting for them to cure for about 5 days before a I pour the hearth. I'll post a pic on my thread at the next stage. Thanks again for the help and idea!

[Gromit]

Re: Round foundation help

Tony,

In the unlikely event that you are wondering whether your concrete columns will support your oven, this video might prove reassuring: Concrete Crusher vs. Concrete Is As Entertaining as You'd Expect - Concrete crusher - Gizmodo

(This is really just an excuse to post a video of something exploding.)

[tony boca]

Re: Round foundation help

David,

Great video! On my next build I'm definitely going with one column.

SONOTUBES RULE!

[fxpose]

Re: Round foundation help

Tony, I will be following this thread closely as I'm also interested in the tri-tube support design.

Neil, I also found your 'Flying Saucer' thread. Went through it with great interest. I love the simplicity of your overall design. Very nice work!

[Neil2]

Re: Round foundation help

I'm halfway through my second summer and having a lot of fun with it. From the oven shown in the "Flying Saucer" thread, I did make a few changes after the first year of use. I cast and installed a slightly longer counter top because I was not happy with the finish I got with the first one (It was well below 32 Fahrenheit when I cast the first one and I think I got some freezing and thus it ended up spalling a bit).

I also replaced the original vent chimney with a double walled one.

This is what it looks like now.

[tony boca]

Re: Round foundation help

fxpose,

Sorry I haven't responded. I've been in Europe for the past three weeks. Hopefully i can post some pictures this weekend and get started on the hearth.

[tony boca]

Re: Round foundation help

Today i bent my 1/2" rebar coming out of the sonotubes. Made a grid of 1/2" rebar spaced 10" apart on top of the rebar coming out of the tubes. Should have taken a photo. Made sure the rebar was at least 4" from the walls. (Needed an acetylene torch to bend the rebar). Poured my cement.

Now i need to decide if i should go with vermicrete or fireboard.

[Neil2]

Re: Round foundation help

Looking good Tony.

The rebar from the tubes bending into the slab is mainly for "punching shear". Your 3 x 1/2 rebar at each tube should be more than adequate for that.

If you are going with the vermiculete I have a suggestion. Step your next form in 2 inches or so from edge of the slab. Don't daylight the vemiculete layer. You can then step back out and fill this 2 inches with concrete, forming a "belt" containing the vermiculete. Run a couple of reinforcing wires around inside the belt and form some vertical groves every 18 inches or so to control cracking.

[fxpose]

Re: Round foundation help

Thanks for your reply Tony. Now that's looking really good!!

[tony boca]

Re: Round foundation help

Neil,

How did you draw your elipse? I have a 21" radius and I think I'm going to cut my soldiers at 21 degrees and aim for an 18" height dome. But, I'm having trouble drawing the eliptical plywood template. Any suggestions?