Newbie Oven Project

[tiomarquito]

Hello everybody,
This is our 1st posting. We are almost finished with the base on our oven project as you can see by our picture. We like the idea of a geodesic dome posted by edschmidt. The oven will have a 36" diameter. If anyone has ideas on possible triangle designs to form the dome, we would appreciate the help.

[christo]

Re: Newbie Oven Project

Welcome aboard!!!

You can also check out David's Geodesic dome made from Bricks. I believe he built a 36 inch oven.

He's got all the calculatoin data there as well. It really helped me when I built my oven.

http://www.fornobravo.com/forum/f8/d...-oven-765.html

Christo

[tiomarquito]

Re: Newbie Oven Project

Thanks for the welcome,
We have looked at David's geodesic dome. We found a nearby supplier that sells 55 lb. bags of castable refractory cement for a reasonable price. We like Ed Schmidt's elegant and simple design. We've done cement casting for some backyard projects and the required triangles seem within our ability. We would like to incorporate the idea of a 1" compressible insulation layer over the 4.5" thick casted heat mass to allow for its thermal expansion.

[christo]

Re: Newbie Oven Project

Sounds like a fun project.

Are you going for individual casted triangles or hex's and pentagons?

Also - was wondering about the thickness. 4.5" seems plenty thick - do you intend to bake alot? if not, I'd think about reducing the thermal mass.

I'm not sure what you mean by flexible insulation - many of us have used the ceramic blanket with very good results.

BTW, Nice job on the base - the color and size of the stone is really cool. I missed the fence behind it during my first look. Did you cast the vertical columns yourself?

Christo

[tiomarquito]

Re: Newbie Oven Project

We are planning on a triangle design using the 2 triangle sizes needed for a 2V geodesic dome. Since most ovens have a 4.5" thick brick lining, we figured that's a good number to have a thermal mass that retains heat for a good while.

We will be using a 1" thick ceramic blanket over the dome (we should have said flexible, not compressible).

The vertical columns were cast using a plywood form with molding inserts to make the pattern on the front. The form was oiled and sealed at the joints with plumbers putty. The form was filled with a 1 part Portland and 3 parts sand mix and have 2 #3 rebar reinforcements supporting the cast railing on the top.

[tiomarquito]

Re: Newbie Oven Project

We've made a mock up of the oven dome using the calculations from a website on 2V geodesic domes. For the 36" inside diameter dome the inside surface has two types of triangles. One is isosceles with two sides of 9.837" angled at 78.7 degrees to the inside face and the third side of 11.12" angled at 82.9 degrees to the face. The other triangle is an equilateral 11.12" on each side with an angle of 79.2 degrees to the inside face.

We've considering reducing the thickness of the dome to only 2.25 " of castable refactory cement. You can see the picture of the mock up for the original 4" thick dome.

[james]

Re: Newbie Oven Project

I'm with Christo. This sounds like a great project. I would vote that the thinner dome will be fine.

You should plan on 3"+ of ceramic insulation (alla FB Blanket), or 1" of ceramic blanket insulation, plus 4" of vermiculite. Those thicknesses are pretty safe to plan against.

James

[dmun]

Re: Newbie Oven Project

My geodesic dome is the thickness of one firebrick, 2.25 inches. There's a hollow thud as you throw a log against the back wall, but it fires up fast, and cooks fine.

[DrakeRemoray]

Re: Newbie Oven Project

Will you have to cure the refractory pieces you cast? Most refractory concrete needs some heat curing to come to full strength. Do you plan to do that in your indoor oven? Make sure that your castable refractory is not an insulating refractory castable. I cast my vent out of an insulating castable, and it was fine, but it is not strong, and does not have the mass you want in the oven...

Sounds interesting, love the dome model you posted!

Drake

[tiomarquito]

Re: Newbie Oven Project

Thank you all for the advice and encouragement. We would never have thought of making a geodesic dome except for the ideas we found on this great forum.

To Drake: Thanks for the warning. We have bags of heavy Mizzou castable refractory cement. The casting instructions supplied by the manufacturer specifies the curing temperature for best results is 90-110 degrees F. After curing, the firing procedure seems to be the same as specified for a brick oven.

[tiomarquito]

Re: Newbie Oven Project

Here is an update on our project. We made wooden models of the isosceles and equilateral triangles (pic. 1). These were used to make 3 isosceles forms and one equilateral forms from wood and extruded styrene foam. (pics. 1 and 2). The foam lined forms distorted a bit resulting in castings that were not perfectly precise ( pic. 3). The dome needed 25 isosceles triangles and 8 equilateral triangles plus 2 half isosceles above the opening and 2 half equilaterals on the opening sides.

[tiomarquito]

Re: Newbie Oven Project

When casting the triangles, we used 55lb bags of castable refractory cement which had to be completely used to guarantee the correct water mix. One bag filled 3 isosceles forms and 1 equilateral form with a little bit left over to make a small brick used for the bottom of the dome (pic. 1). The cement was easy to work with even though the water added at first appeared to be too little. After working the mix a few minutes it became plastic and formed easily into the forms by vibrating and tamping. They hard set in 16hrs. in a warm location.

[tiomarquito]

Re: Newbie Oven Project

This is the latest news on our project. The photos show the assembled chimney above the entrance to the stove and the ceramic blanket wrapped around the dome and chimney before the perlite insulating concrete was applied.

We're just about ready for the initial heating to cure the castable refractory lining of the stove. We're wondering the best way to gradually raise the interior temperature to around 300 degrees and maintain it for the suggested 24 hours without having any "hotspots" on the floor? Thanks for any helpful tips.

[staestc]

Re: Newbie Oven Project

Thanks for posting the new pictures! Very nice build! This is the first I have seen of your oven build, and it just looks great!

Travis

[tiomarquito]

Re: Newbie Oven Project

The latest report on our project is that we've fired the stove and worked up in stages to 1000 degrees. The outer dome surface temperature never exceeded the mid 80's. Thank you Dmun for telling us about Royal Oak Lump charcoal for oven curing. It was the only way we could control the temperature at 300 degrees all day on the initial firing. Thank you Tracy for your encouragement.