Insulation layer/order on top of the dome

[Brodek]

All,

I am building a barrel dome oven, based upon Alan Scott's design. For insulation under the oven floor, I have 4" of castable cladding on-top of the base, with an additional 2" of ceramic fiber board. My question is about the order of insulation on top of the dome.

My plan is to cover the dome with 3" of ceramic fiber blanket, and an additional 4 inches or so of the castable cladding. But...will I lose the "mass heating" that is a part of these ovens? I believe I understand the oven heats a large mass of material, that then radiates heat for a number of hours. If, I cover with 3" of ceramic blanket, have I negated the mass heating aspect of the oven? Should I do 4" of cladding first, then the 3" ceramic blanket? Thoughts or learnings here?

Kevin

[Wiley]

Re: Insulation layer/order on top of the dome

Hi Kevin,

From what you wrote I took away that you placed the insulation on top of your cladding on the base? Did I read that wrong? I hope so because the insulation goes on top of the support/base with the cladding and hearth bricks on top of it.

Castable cladding is a non-insulative material and a heat sink/reservoir. So the correct order is to place it on the dome and then place the insulation over it.

Hope this helps,
Wiley

[dakzaag]

Re: Insulation layer/order on top of the dome

I read the post slightly different. You have a support base and then an insulating cast layer and then a ceramic fiber board. This is the correct order, maybe I didn't read what was posted properly. I guess I don't know what you mean when you say castable cladding. Cladding is a term to describe the outer surface such as siding or brick veneer. Underneath an oven it would be just structural support. Unless it is insulating and then it would be an insulation layer.
On the dome, first of course is the brick, then insulation which you said was ceramic fiber blanket then a castible cladding. Again this is somewhat confusing as very few builders cast their outer layer. I have stucco'ed the outer layer by troweling on stucco mix. If your cast cladding is heavy, it will compress the ceramic fiber and decrease the insulation value. 4" could be pretty heavy if it is cement but you can put a dense cladding on the outside of the insulation if you have a way of preventing the compression of the insulation.
In general insulation should be the first material that comes into contact with the underside of the floor and the dome of the firebox.
If you were to cast 4" of whatever against the dome, you would have 8-9 inches of mass to heat up. While it would cook for a week, it would take three days to heat up and require a small forest to keep up with the wood supply.

[Brodek]

Re: Insulation layer/order on top of the dome

Both,

Thanks for your replies. I'm certain I've created a fair amount of confusion with possibly incorrect terminology...so I'm going to back-up a step to clarify. For the record, I am building an Alan Scott design bread-oven, that will rely on stored heat/energy for baking bread once the fire is removed. I am building it off of plans (really pictures) from Rado, in Australia (Wood pizza oven Building wood burning brick bread ovens) So, I'm building the oven for good heat storage, versus just high-heat applications like pizza.

Currently, I have a block support structure, with concrete pavers as the support layer for the more specialized WFO materials. The first layer over top of the concrete support layer is a 4" layer of Econolite (PryorGiggey | Insulating Castables). This was a Pryor Giggy product that my supplier called "castable insulation", and recommended for the floor insulation. A picture of this layer is included below. Before my partial tear-down yesterday, I had put a layer of ceramic fiber board on top of this layer...then the floor of the oven (medium density fire brick). After thinking about it, and reading some more..and getting a few comments, it appeared I may have virtually eliminated the "mass heat storage" under the floor, by placing the fiber board on top of the Econolite layer, so I'm now back to just the layer of Econolite on the concrete support.

My plan, I believe, is to now pour a 4"/5" inch layer of refractory concrete over top of the Econolite layer to serve as my hearth slab. This layer will be 1:1:1 combination of portland cement, lime and fire clay. The concrete and lime come together in a masonary cement (type N) from Quickcrete. I will add the Hawthorne 40 fire clay to the Quickcrete product.

I believe I understand that this layer serves as an additional heat-sink for the oven, storing heat/energy for usage after the fire is removed. So as I understand it...the base (Econolite both stores some heat, but serves mostly as an insulation layer. The hearth slab stores more heat, and is able to do that without disintegrating because of the 1:1:1 mixture. On top of this hearth slab, I will mix 1:1 fireclay and sand to serves as a leveling surface for the medium density fire brick.

Do I have this correct? I've got some really nice plans...actually pictures from a gentleman named Rado in Australia...literally 2,000+ pictures of the build. But the text and description(s) of the build is a bit light!

What I have available along with the above mentioned is some ceramic fiber board...but I can't see a need/use at this point. It probably would have been great UNDER the Econolite...but I don't believe I've created enough of an issue to create a tear-down to the concrete support layer. I can be corrected here, if necessary. I still have bags!... of the Econolite, and enough cement, lime and fire clay to create my own city!

Plans for the dome will be the fire brick with home brew mortar for the joints (3:1:1:1 Sand, portland cement, fire clay, lime. Then, a 4" layer of the refractory cement (1:1:1: Portland cement, lime, fire clay) Then another 4"-6" inches of the Econolite. And finally, a final layer 2"? of ceramic fiber blanket.

Really open here to feedback, thoughts, corrections, even laughing! Really appreciate the help.

Kevin...with an oven that moves ahead a step, then back two...then ahead again...

[dakzaag]

Re: Insulation layer/order on top of the dome

No laughing here, just be aware, what you are building has 6-9 inches of mass that will need to be heated. It will take a whole day of constant firing to get all that mass up to an equalized bread baking temperature.
The good news is that once you have got all the mass warmed up, you will be able to bake for a couple of days before firing again. This amount of mass would be typical of a commercial situation that fires every day or two without ever letting the oven cool down and bakes every day or every other day.
If you plan to use this oven 1 or 2 times per week, I think you are way over building it. If it will be used every day then carry on.
There is never too much insulation so if you have ceramic board on hand, I would recommend you install it on top of your castable insulating layer.

[Tscarborough]

Re: Insulation layer/order on top of the dome

Rado seems like a really nice guy, but his ovens (and Alan Scott's), are really not that good a design, even for commercial use.

In my experience, the oven will perform as designed, but will not get much use down the road because of the expense (in wood and time) required to fire it.

Unless you are seriously going to fire it 3 or more times a week and produce salable amounts of bread, the normal Pompeii oven will perform exceptionally well as a bread/pizza oven, and will not require as much wood/time to fire.

[GianniFocaccia]

Re: Insulation layer/order on top of the dome

+1 on Tscar's assessment. There are a number of builders (Tscar included) who have moved past and improved on the Alan Scott design and built a more-efficient, higher-functioning oven.

Bill's barrel vault is an example:

http://www.fornobravo.com/forum/f43/barrel-vault-so-cal-17285.html

BTW - Any cast oven floor using portland cement is a bad idea. For an oven of your scale, I would stand my firebricks up on their edges to make a 4"-thick floor.

[Wiley]

Re: Insulation layer/order on top of the dome

Kevin,

When I was composing my reply to your initial question I did a search of the term "castable cladding" because I wasn't sure of what you meant. Oddly enough a page came up on that search that was Rado's:

Concrete oven cladding applications for wood oven dome.

That's why I guessed you meant thermal mass rather than some sort of stucco outer layer.

Without raining on Rado too much, Tscarbough has it right. Basically inefficient designs requiring a forest or very deep pocketbook to fire them regularly.

But such WFOs are built, check archives. There is one not too far from where I live that has a huge thermal mass/heat storage and no insulation. His name is Phillip and yes it takes hours and hours and a huge amount of wood to fire his WFO. But he does fire it regularly and donates most of his production to the local food bank. Good on him.

So maybe you have the forest or the deep pocketbook and don't mind getting up in the wee hours of the morning to start the fire for a midday bake.

It's your WFO, you get to build what you want. We are here to help where and when you want it and where and when we can. You are not the first to find FornoBravo in hopes of salvaging a design found elsewhere. Read the archives.... there are some real nutcases offering designs out there. Most claiming they have the best design and know all there is to know about WFOs.

Hope to help,
Wiley

[Brodek]

Re: Insulation layer/order on top of the dome

OK Tscar/All,

So, what I believe you are saying is that I could:

Put my ceramic fiber board (2") back down, and lay my fire brick on edge (4") all of top of my Econolite, and be more than fine.

Fine (defined) for me seems something like this... I can envision having folks over for a pizza night on Friday night, and then baking the following morning. Would realistically not do more than 1/2 bakes for bread. Reasonable expectation with the above layout?

Gianni,

I'm interested in your thoughts/experience on what would be a better slab material over top of the Econolite. What I have available in quantity is:

Lime, portland cement, 2" ceramic fiber board, sand, more econolite.

And, at this stage of my build, I can still pull-off either a barrel or an adobe shape with the firebrick.

Please keep the comments coming...I've read until I'm weary..and have changed my mind often...but hoping to land on the "best" build for my use case above.

Lots of materials on hand...and not really financially pressed, so many options can be considered.

Kevin

[Brodek]

Re: Insulation layer/order on top of the dome

Wiley,

Thanks for your comments... Came-in just as I was composing my note above. I too, am not here to cast judgment on anyone's design, etc... Just trying to build an oven that works best for my situation. And, really, REALLY appreciating the input/advice from here.

So, not being married to any design yet, I am in pursuit of the best options available for me expected scenario of Pizza in the evening, then a bake or two in the morning. Realistically, probably a single bake the following morning. Yes, I live on a farm, but I don't want to cut all of my trees to fire my over!

As I said, I've gotten some pretty great materials, so I can combine them in any order and shape.

Appreciate your advice. Really do.

Kevin

[GianniFocaccia]

Re: Insulation layer/order on top of the dome

Kevin, my routine has been to do pizzas on a saturday evening and fully saturated, close the oven up right away. By 1-2pm the next day my bread is ready and my oven is about 425-450F, so in it goes. With ~4.5"-thick dome, the oven is good for one batch.

I am partial to the pompeii shape because it is so efficient at many things (pizza, roasts/casseroles/bread) Not as efficient as a barrel vault (footprint) for bread, but its a good tradeoff. Building a pompeii oven is three times the work of a barrel vault though. I put 2" of CF board on top of 3.5" of vermicrete. Put the board on top of your castable insulation and you will be golden.

[Tscarborough]

Re: Insulation layer/order on top of the dome

The only thing I will add is that a 4.5" thick floor is very thick. The floor is by far the hardest part of the mass to heat up.

I generally do the same as Gianni; pizza at night, bread (or other things) the next day or 2. A thinner (2.5") floor will heat quicker, and then when doored up overnight, fully equalize with the rest of the oven.

[dakzaag]

Re: Insulation layer/order on top of the dome

I just wanted to let you know about our turkey we cooked in the oven on Easter Day. We fired the oven on Sat. nite for pizza and then I kept a hot fire going until about 10:00 pm. Temps were in the high 700 when I put the door on. At 7 am Sunday morning the oven was about 550 F. We put the turkey in at noon and the oven was at 450. Turkey was done at 2:30 with an internal temp of the bird at 185. (16# bird ) the oven was still 350 at that point. I checked the temp again around 8pm on Sun evening and the temp was still 300. I don?t believe this oven has enough insulation under the floor, as the base warms up when it is fired, but the dome is well insulated. I believe this performance would be satisfactory for baking bread. I burned a small wheelbarrow of wood from Sat. about 4:30 until the last wood went in around 9:00pm. This oven has 2.5? floor brick and 4.5? dome brick. This is just an example of what kind of performance you can get from the oven. My oven is a round dome, but for bread I would suggest a barrel style. It is also easier to build the barrel style

[Brodek]

Re: Insulation layer/order on top of the dome

Dakzaag,

Thanks for the detailed reply, and associated temps. Narrowing down on my decision. Lots of help here.