Before pulling the trigger, in need of criticism

[brickie in oz]

Re: Before pulling the trigger, in need of criticism

It is used as lining outside the refractory lining.

Apologies for any language barrier.
If its used outside its a cladding.
If its used inside its a lining.

[lwood]

Re: Before pulling the trigger, in need of criticism

Sounds like you are trying to plow up new ground. Why don't you want to use the standard vermicrete insulation. It was good enough for all of us. Many of us can debate the benefits of different materials with you. But we have had all those discussions previously. I don't think you are going to get much better insulator than vermicrete. My belief is that the air pockets in the vermiculite contribute more than anything to the insulation properties.

[giol]

Re: Before pulling the trigger, in need of criticism

I agree that the tried and tested is always the best but since i am building this in my balcony which is paved with white marble tile, i want to use the less meesier way possible. Additionaly the cost difference of the two ways is minimal here in Greece (portland cement costs 0.8 Euro /kg while the ready mixed 1.2 and vermiculite is expensive because it is imported). I am not at all experienced with cement mixing and stuff like that so i tend to trust the profeesional product more than my own capabilities.
By the way i am using vermicrete, it is the same materials (cement,vermiculite, water and san) except for the cement which is calcium aluminate type (like cement fondu and secar 71).

[shuboyje]

Re: Before pulling the trigger, in need of criticism

OK so we have 0.19 w/m/k let's not bother converting, I like to work in metric anyway.

Here are some common insulators:
Cal-Sil - 0.05 w/m/k
Fiberglass - 0.04 w/m/k
Mineral Wool - 0.04 w/m/k
Perlite - 0.031 w/m/k
Vermiculite - 0.058 w/m/k

Now let's look at some of the false insulators that tend to be used in Europe:
Tuff - 0.5-2.5 w/m/k
Dry Sand - 0.15-0.25 w/m/k

You can see there is a full order of magnitude between the two, and your product is clearly in the false insulator range.

[giol]

Re: Before pulling the trigger, in need of criticism

Thank you all for the comments on the insulation. I hope i am not offending anyone by insisting on my point.
Here in Greece every other house has wood fired oven. I have two , one 60 years old cobb oven made by a widow (tradition) and still in use in my village house.A second one with firebrick ,clay and straw in my father house. It is a long tradition. There a lot of different styles but the guys that sell refractory (especially in the factory where i bought it) know exactly what it is and how it works. This factory is also the main producer of firebrick in Greece and they also sell pre-cast modular wfo to commercial pizzerias. The thermal conductivity of the product is very close to the ceramic fb the pompei oven document suggests. I add the calcium silicate AAC which is also insulating. For 50 euros i got the oven floor ready with commercial grade material.
Please send me some comments/proposals about the shape of the oven if you can.

[shuboyje]

Re: Before pulling the trigger, in need of criticism

The most famous ovens in the world are hand built in Naples Italy. The use Tuff for "insulation" and pour heat out in every direction. In a commercial setting it doesn't really matter because the oven is always hot. In a home setting where you fire infrequently it is far from optimal. There is pretty well known guy online who has one of these ovens at his home. He generally fires for 10 hours to cook Neapolitan pizza.

Like I already stated the numbers don't lie. You are free to use whatever you want, but take a look around this forum and read ALL the threads from people who have built ovens without insulation under them trying to fix their oven because it isn't working. I'd hate to see you in that situation when you've already been warned about it. If you build as planned your oven will be uninsulated under the hearth. You might as well save your money and build on a bed of sand, it has the same thermal conductivity.

[Tscarborough]

Re: Before pulling the trigger, in need of criticism

Again, engineers know what they are about, but they are often focused on one set of design criteria, while the desired goal, which is only slightly different, makes a huge difference in the end.

As an example, in unitary masonry construction there are very few engineers who specialize. Usually concrete engineers do the work, since both concrete and masonry share portland cement, aggregate, and often reinforcing steel.

The reality is that concrete engineers make crappy masonry engineers because their focus is on strength, compressive strength to be exact, which is not the over riding concern of mortar and reinforced or un-reinforced unitary masonry designs.

If you are designing a commercial kiln, then you do not use the same insulation criteria that you do for an intermittent use home oven.

[giol]

Re: Before pulling the trigger, in need of criticism

Guys my next question is about the cooking floor. I have around 30 firebricks wich are thin: 22x11x3 cm (8.6x4.5x1.2 inches). I get these for cheap from a hardware superstore chain. I was thinking of making my floor with this but in two layers so i can get the 2.5 inches thickness. My idea is to make cross like pattern of firebrick as a first level and fill the circle with insualting concrete instead of cutting bricks for this level. The top level ofcourse will have common pattern use here and will be made by firebrick only, with the cuts required.The floor will be 2.5 inch thick in the center , on the two sides and the back. But onlt 1.2 inch thick on the edge of the 4 corners. Is it a terrible idea?

[ATK406]

Re: Before pulling the trigger, in need of criticism

My first peice of advice is, don't go "cheap" on your cooking floor. That is where all the action is;

But if you must use these 1/2 bricks (they are called "splits" here in the US); Constructing a floor that does not have a uniform thickness of firebrick will result in a floor that does hold heat uniformally. The thicker sections will take a little longer to heat up because of the extra thermal mass, but the thinner sections will cool down more quickly due to lack of same. Your current plan is to place them in the shape of a cross (and maybe that is ideal) but I would arrange them to optimize the shape/size of your cooking surface.

In time you may identify some advantage to this (I have found that varied temperatures on the surface can be usefull if you are cooking more than one pizza at a time) but it will take some practice to learn how your own unique oven performs.

Reagards,
AT

[giol]

Re: Before pulling the trigger, in need of criticism

You reckon that having two layers of firebrick is less efficient than one of the same total size? I expect to have only some very small patches without two layer firebrick near the perimeter of the dome (to avoid cutting the fillers two times).

[ATK406]

Re: Before pulling the trigger, in need of criticism

You reckon that having two layers of firebrick is less efficient than one of the same total size? I expect to have only some very small patches without two layer firebrick near the perimeter of the dome (to avoid cutting the fillers two times).

Not at all. I was refering to the layers that would be only 1/2 thickness. If those will be limited to the perimeter of your floor, you've got nothing to worry about.

[Tscarborough]

Re: Before pulling the trigger, in need of criticism

Actually, 2 layers will always be less efficient than one unless you get 100% perfect mortar coverage between them. Heat transference.

[giol]

Re: Before pulling the trigger, in need of criticism

I was thinking not to mortar them at all. Just stack them and fit them in the dome.

[giol]

Re: Before pulling the trigger, in need of criticism

Now a question about the arch. In the fornobravo.com front page, the photograph that has a subtitle "residential oven" depicts an oven with an entry arch i really like. Do you think i can do that with castable?

[brickie in oz]

Re: Before pulling the trigger, in need of criticism

Now a question about the arch. In the fornobravo.com front page, the photograph that has a subtitle "residential oven" depicts an oven with an entry arch i really like. Do you think i can do that with castable?

No.......................