separating arch from inner dome and floor

[david s]

For my oven I separated the dome from the outer arch with 10mm of vermicrete for two reasons.
1. It provides some insulation so less heat is lost by conduction to the outer arch.
2. The outer arch remains relatively cool to touch for safety. (warm not hot)
3. It provides some protection from thermal expansion and resulting cracking around the arch.

My question to other oven builders is... How hot does your outer arch get, and do you get some cracks around the arch?

I notice that the Pompeii oven arches all seem to be connected to the inner dome.

[ThisOldGarageNJ]

Re: separating arch from inner dome and floor

My question to other oven builders is... How hot does your outer arch get, and do you get some cracks around the arch?

Mine will get to around 200 degrees (f) I havent had any cracks,,,

Mark

[papavino]

Re: separating arch from inner dome and floor

I was wondering about the cracks in the outer arch, too. I just finished up my decorative arch this weekend, so it'll be a few days before I fire the oven back up. I'll let you know if the arch develops any cracks.

[Dourdd]

Re: separating arch from inner dome and floor

This is such a fantastic idea...I actually came across it independently from you, too!!! Except I was going to use insulating (kiln) firebricks; but I like your vermicrete idea.
(my other idea is metal "stringers" between the cook floor firebricks and the isolating surface (vermicrete, or whatever) to evenly distribute heat from the bricks directly under the flames to those further away from the flames)

Now, to my couple questions:
Why did you choose 10mm, as opposed to something thicker...structural reasons?
Also, can you say how hot your oven stays due to this isolation? For example, assuming you have a door to seal in heat, how hot is your oven the next morning?

[david s]

Re: separating arch from inner dome and floor

We all talk about how important insulation is, yet many WFO's arches are directly connected to the inner parts of the oven and not insulated. My oven's arch gets hot but not so hot that you can't keep your hand on it. With only 10mm of vermicrete separating it from the rest of the oven the insulation is not perfect but must stop a lot of heat conducting to the outer arch. My oven is still pretty hot in the morning although if I'm not going to use it again the next day I like to leave the door off so it doesn't get cooked. Why trap the heat if you're not going to use it?

[nissanneill]

Re: separating arch from inner dome and floor

David.

My oven is still pretty hot in the morning although if I'm not going to use it again the next day I like to leave the door off so it doesn't get cooked. Why trap the heat if you're not going to use it?

You do have a point with retaining the maximum heat or rather minimum heat loss with your 10mm vermicrete layer between your oven and chimney void. I didn't worry about that as I don't plan on baking for 24 hours after doing pizzas. I bake on the same day and not the next. Even if I were to build another oven, I would not change my build as I have no cracks at all.
However, my front arch bricks get warm only and that is from the fierce fires that I make to get my oven up to 500˚C in just over an hour, after cooking pizzas, usually a couple of hours without renewing the fire. I close my oven up and it is still 250˚C next morning so it retains plenty of heat.
I do however have a rather thick steel curved lintel welded to heavy steel angles in the oven entrance which float freely in the grooves cut into the adjoining firebricks, soldiers and the next few courses, so that there is no reaction from different thermal expansion of the dis-similar materials. To this frame I welded some stainless angle which holds the fibreglass sealing rope which helps seal completely the oven.

Neill

[Neil2]

Re: separating arch from inner dome and floor

"Except I was going to use insulating (kiln) firebricks;"

This is what I used. I also created a heat break via a one inch ash drop gap between the hearth brick and the countertop the full width of the opening.

[Dourdd]

Re: separating arch from inner dome and floor

Neil2,
Fantastic! Thanks for popping in and sharing that.
I'm gathering information for my build which I hope to begin in 8-12 months...once I actually have a backyard!!!
I enjoyed viewing your "flying saucer" build thread...looks really nice, especially the angled counter top which I would also probably like to copy!

[karl]

Re: separating arch from inner dome and floor

Hi,

What do you define as the inner and outer arch? If you count the intergrated arches with the flue gas exit as the "inner arch" and the outermost "entrance arch" as the outer arch I fully support the insulation idea. I would not recommend to put any insulation between any parts of the integrated flue gas arches though. It would cause build up of thermal stresses in the flue gas manifold part.

karl

[Neil2]

Re: separating arch from inner dome and floor

"For example, assuming you have a door to seal in heat, how hot is your oven the next morning?"

I have an insulated door. I go up to 1000 for pizza at 5 pm. About 7 pm it is about 600. If I put on the door it will still be 300 at 9 am next day and about 220 at 2 pm. I then put in my slow roast or pulled pork and it is ready for dinner at 7:00. All on one, 1 hour firing using a about 1 1/2 cubic feet of wood.

If you pay attention to the insulation, these things are amazingly efficient.

[david s]

Re: separating arch from inner dome and floor

"What do you define as the inner and outer arch? "

You are the first one to mention an inner arch, However the intention is to retain the heat in the dome, so it would be logical to reduce conduction of heat to the flue entry/manifold/ gallery/ or whatever you like to call it. This may not be practical and anyhow it is usually insulated, unlike the outer arch that is uninsulated and open to surrounding ambient temps.

[nissanneill]

Re: separating arch from inner dome and floor

David,
like or unlike most other oven builders, I have 2 arches as per shown in the attached pic.
The inner arch bricks are sitting on a lintel steel bar which is curved to meet the shape required, ie. the same contour as the outer arch.
The outer arch does not get hot but I do have a rather large chimney void where all the smoke and hot gasses rapidly escape.
Behind the front arch bricks is a 19mm compressed cement sheet which was used to cement the paving bricks to and remains as a reinforcement for the front panel.

Neill

[ThisOldGarageNJ]

Re: separating arch from inner dome and floor

Neil,
Did you glue the rope seal directly to the oven ? If so is it working ok ?
I was thinking of that but wasnt sure if it would hold ...
Mark

[jmhepworth]

Re: separating arch from inner dome and floor

I was thinking of attaching the rope to a wood door. How should I attach it?

[ThisOldGarageNJ]

Re: separating arch from inner dome and floor

they sell refractory rope kits for boilers on ebay,, they are less than 20 bucks.. THey come with a glue to attatch them,, Im sure you could nail/screw/glue it to the door and it would be ok... I just like the Idea of attatching to the brick.. I guess I am gonna have to break down and order 2 so if the glue doesnt hold I can attatch it to the door

Mark