Igloo style oven

[marc boulay]

Hi everyone,

I want to build a 42? Pompeii oven, igloo shape insulated with 3" ceramic plus insulated concrete, no enclosure. This oven will be built inside a new sun room/extension to existing garage, this new place will be heated with a wood stove occasionally.

I would like to know if this is made for cold weather.

I am worried about the expansion, the way the hearth is constructed over the oven stand (structural slab and insulating layer).

Is this suitable for cold Canadian weather?

And is it easy to smooth out the insulated layer (vermiculite concrete) to receive the fire bricks?



Please help,

Marc

[eprante]

Re: Igloo style oven

Marc,
there are many ovens in the north that have held up very well. See the link below. The vermicrete is weird but easy to work with. Search through the photo gallery and you can find pictures of ovens in all stages.

Good luck,

Eric


PhotoPlog - Finished Ovens

[dmun]

Re: Igloo style oven

A mixture of sand and fireclay is put on top of the vermiculite layer to smooth it out for the floor. This can either be mixed with water and applied with a notched trowel, or put on dry, the floor laid, and when you're satisfied with the level, then you wet the floor to set it.

There are some complications to building an oven inside your house, mostly having to do with building code. The oven will have to be built to masonry fireplace standards, and have a proper flue. You may not be able to share a flue with your woodstove. This all depends on how many hoops your building inspector will make you jump through. Building departments tend to be more rigorous in more populated areas.

[marc boulay]

Re: Igloo style oven

Eric,

so my main question is if the oven is well insulated 3" ceramic and insulated concrete and all the needed stuco over it is there a need to have an insulated enclosure?
This oven will be inside a extension to my garage, and will have a saperate chimney.
Will the oven perform well without this enclosure? Will there be problems to attain high temps?
I really like to have the igloo shape.
Also, i have seen on other sites that the hearth is suspended on the block stand with rebar, insulation concrete poured first top by the structural concrete, making the hearth and stand seperated for expansion.
Is the difference/advantage with insulated concrete over the structural slab, like the Pompeii plans.

I am new to this and any help is greatly appreciated.

Marc

[eprante]

Re: Igloo style oven

Marc,
the answer to your first question is that if your igloo is insulated according to the FB plans then there is no need for an enclosure for heat retention. The decision to build an enclosure or igloo style oven is personal choice based on aesthetics not function.

As to the second question why some other sites recommend placing the insulation layer under the structural layer; I dont understand the practice unless it is to add a ton of thermal mass to the floor of the oven. It seems to me that an oven with 4 inches of concrete under the cooking floor would take a very long time to heat up. You would use much more firewood with that design. If you want more thermal mass under the floor, you can add an additional layer of firebrick, much easier.

If you are intending to have the oven in an enclosed space, I would pay close attention to making your flue design large so that you don't have issues with the smoke exiting the front of the oven. Some people make the flue 1/2 a brick wide, others use a full brick width
good luck
Eric

[dmun]

Re: Igloo style oven

You understand that there is a solid dome, of firebrick or similar, covered by an insulation layer, either vermiculite concrete, or a refractory insulation blanket? Your description " 3" ceramic and insulated concrete " seems a little ambiguous to me. Once you've got the dome and insulation, the covering is strictly waterproofing and decoration.

I've also never understood the practice of suspending the entire mass of your oven by a few skinny horizontal rebar pieces. It doesn't allow for expansion - bare rebar expands more than concrete. It doesn't allow for a lack of thermal bridging - rebar conducts heat better than masonry. To say nothing of putting the insulation under the structural support. It seems like a bad idea all around.

[Tscarborough]

Re: Igloo style oven

"bare rebar expands more than concrete"

If this were true than modern reinforced concrete structures could not exist. As it is, concrete and rebar have almost exactly the same coefficient of thermal expansion. One of those lucky coincidences that allows us to build modern concrete structures.

[marc boulay]

Re: Igloo style oven

dmun,

please see Pompeii plan, page 56, photo 13.3, FB blanket covered with wire and insulating concrete, it is hard to see how thick this insulating concrete is over the wire and blanket, so what would be considered sufficient thk?

Marc

[dmun]

Re: Igloo style oven

Can someone else cover this question? I don't have the PDF instructions at hand.

[eprante]

Re: Igloo style oven

The rule of thumb is 3 inches of ceramic blanket, or 4 inches of insulating concrete. Some people have used both (see sjmeff). If you are concerned about heating up your room form radiating heat off the dome, you could put an extra layer of perlcrete over the ceramic blanket or do 4-5 inches of blanket. You are in Canada so a little heat radiating off the dome probably isn't going to be a bad thing.

[james]

Re: Igloo style oven

I think the rule is 3" FB Blanket or 1" FB Blanket plus 4" vermiculite concrete. The blanket is roughly twice as efficient as insulating concrete.

For a commercial oven in use 24/7, or for an oven that you want to use outside in extreme weather, you might want to go to 4" of FB Blanket on the sides and 6" on top.

With these thicknesses of insulation, your outer enclosure won't get hot at all.
James

[james]

Re: Igloo style oven

One more thing. You always have to build an enclosure of some sort to hold in the insulation, even if the oven is indoors. You don't want to leave either FB Blanket or vermiculite exposed to the air. At a minimum, you can follow the shape of the oven with stucco lath and apply a basic stucco coat.
James

[marc boulay]

Re: Igloo style oven

James,

so 3" FB Blanket should take care of the insulation part.

I was confused by the page 56, photo 13.3, FB blanket covered with wire and insulating concrete. That photo is probably showing a combination of both insulation.

So this 3" FB Blanket only needs to be covered with stucco lath and a basic stucco coat?

This is a great forum, many thanks to everyone who's helping me out.

Marc

[Neil2]

Re: Igloo style oven

Marc

Where in Canada are you ?

I think the only cold related issue you have to specifically address is frost heaving in frost susceptible soils. If you have granular soils, just build a slab.

I have an Igloo style with no enclosure and I just cover it with a tarp in the winter.

[marc boulay]

Re: Igloo style oven

Neil

we are in NewBrunswick.

i still haven't excavated the area where i am making this extension 14'x26', but i know there is top soil to be removed, then add new dry compactable material. The floor slab will be 4" thk with 8"thk x16" perimeter, arround the stand (rectangular shape) it will increase to 10" thk x 24" wide (wtih rebar to match). Once the slab is poured and cured, then i am pouring the stand (8" wide wall), not using block. 3 sides of the stand will have arch opening, the back of the stand will be full wall. The forms made of 3/4' plywood, arches forms laminated and rolled (2) 1/4" plywood. This stand will be designed with rebar and tie with the hearth re-bar. The slab for the hearth will be
8" thk x 3" at perimeter with a recess area for pouring the 4" insulation concrete. I will be providing drawings i the near future. Did found fire bricks @ $2.00/brick not used but little dirty.

P.S. Did anyone purchase a masonry saw and able to give me the brand and what they paid for?

Any comments, anyone?

Marc