Building oven whilst Coronavirus in NYC

[NYFirinci]

Hello everyone,

I am new here. I started building my oven beginning of March, however due to Coronavirus hitting NYC hard, I had trouble going out to get products or even order them online because they would take forever to ship. My biggest concern is insulation in the base of the oven and overall insulation. I was able to get rockwool heat resistant up to 2300 degrees Fahrenheit I believe. I placed this on the bottom of the oven which was about 4-5 inches thick, then put a fence over it to pour concrete mixed with perlite. Over that layer I placed concrete bricks to make it more stable because it was bouncy. Then I poured bond mixed with perlite over the concrete and placed the 1inch fire bricks. Is this enough insulation for the base of the oven or will it not hold in enough heat for the base? Would greatly appreciate the advice. By the way, I have no knowledge about building or construction. So please don’t judge if I did everything completely wrong

[JRPizza]

Welcome to the forum and glad to see you have been approved to post. I'd recommend pausing your build till you can get feedback on what you have done. Pictures of where you are at right now would really help anybody that had suggestions. Would also help if you had links or better descriptions of the products you are using, like the insulation and your bricks. I can say right now that a 1" layer of thermal mass for the floor is not going to give you much extended cooking time. You should also spend some of the quarantine time reading some build threads to see what others have done - I am not sure I have seen any builders take the approach you have described so far.

[NYFirinci]

Hello JRPIZZA, thank you for the reply. I have lots of fire bricks over, 2 styles 1 is 1inch thick the other 3.5 inch thick. I can stack the 3.5 inch on top of the existing 1inch firebrick, but would I need more insulation for the base? I used rockwool R15 that was 4inches thick. On top I used Rutland Refractory cement that can hold up to 2000Fahrenheit mixed with perlite. About 1 inch thick then I placed concrete brick over. Then I used this Bond that the masonry store recommended for ovens. I put the bond over the concrete bricks and laid the 1 inch fire bricks on top of it. I can still add another layer of 3.5 inch thick firebrick on top of the existing firebrick or should I put another layer of insulation and then firebrick, I’m planning to cook lamb, breads, pizza so I made it quite big. About 40x40 inches of inside space. I’ll include some pics on what I did last. FYI the front entrance is not done, I just stacked bricks to see how it looks. But I did add a clean out door which I can remove if it’s unnecessary. The entrance for putting in food is 18inches and and 13 inches high. Also this is a Cube style, back when I was in Turkey they would build Cubed style ovens which is why I thought it would not be a problem. Any criticism helps. Thank you.

[JRPizza]

Wow, a cube! That is so far from anything I have ever seen or read about I don't even feel comfortable offering advice. Hopefully someone on the forum can offer help. How well do you know the cube design - do you have plans or are you just winging it?

[NYFirinci]

Well in Turkey, I used to work for an “Oven” just baking bread and roasting lamb or whatever the community gave me to cook In the oven. I’m not a builder, but I know how to manage fire, baking, dough work, butchering. The oven I worked with was huge and square, not round or dome shaped, I would crawl in to clean the inside of the oven. Just don’t know how it was built. I wanted to bring back my memories buy building a similar layout but I don’t know anything about insulation, so I was hoping for some advice before I end up with a big fail. Thank you again for your reply.

[david s]

Whilst a cube for a kiln or oven is simple to construct it has two main problems. Firstly it is difficult to achieve good circulation to create an even temperature in the chamber. The corners typically are a bit cooler. This is far less of a problem for an oven than a kiln which requires particularly even temperature for maturing the glazes. Secondly because of thermal expansion the integrity of the structure is challenged. Once again it’s a greater problem in kilns than ovens because the service temperatures and the resulting thermal expansion they see are about double that of an oven. However, the same principles apply. A hemispherical dome while more difficult to build, is self supporting and although it may experience some cracking from uneven thermal expansion, can’t collapse.
The difficulty with a cube is how to support the roof. There are a couple of methods, but the most usual one is to create a slight arch called a vault. This will support itself but requires bracing at the top of the walls. Research barrel ovens to check this out. Another method, which I once used for a kiln was to drill through the ceiling bricks and hold them together with threaded rods.

[NYFirinci]

Thank you for the advice David. I guess this explains the constant shoveling of coal and wood I used to throw in through the chamber with the oven I used to work with. That is where I got the idea of installing a chamber door. I guess I will look into building a vault.

As for the oven floor, should I stack another 2.5 inch of firebrick on top of the existing 1.5inch firebrick it should I add a 1inch ceramic fire board and then cement it and then add the 2.5 inch firebrick. Let me mention again under everything I have a 4inch thick rockwool R15 heat resistant insulation

[david s]

I’m not familiar with the rockwool product you have, but I used rockwool blanket over the dome of a couple of ovens rather than ceramic fibre blanket and found it was too compressive, making it difficult to add a vermicrete layer on top of without it compressing. Generally the underfloor insulation needs to be able to support 100 psi or more. Will your product support the weight of the floor bricks without compressing. If not you are squeezing out the air spaces reducing insulating capacity. Oven floors are generally around 2” thick, but you can go more or less. A thicker floor will take longer to heat up, but retain temperature better. Conversely a thinner floor faster heat up poorer heat storage.
Don’t put insulation between layers of dense floor brick.

[JRPizza]

To add to what david s said above, most folks use a blanket product to surround their dome (non weight bearing application) and either an insulating board or a concrete/insulation mix under their floor bricks to take the weight of the floor and dome above. If your floor product was blanket you might want to consider a "reboot" of your project to build a stable insulating floor. If you stick with a design that is inherently less stable than a dome you are really going to need a stable base.

[NYFirinci]

Here’s a description from Home Depot:

• Fire resistant due to its high melting temperature of 1177°C (2150°F)
• Excellent sound absorbency growth
• Water and moisture resistant; does not absorb moisture to maintain insulating value
• Easily cut
• Does not rot or promote growth of fungi or mildew
• Flexible edge springs back, expanding the batt against the frame studs to provide a complete fill

It was 4 inches thick and another name of it is mineralwool

[Chach]

I don't believe you'd be happy with that under the floor. That stuff is not dense enough to support the weight of the oven.

Ricky

[NYFirinci]

Chach Thanks for your input. I did notice that it was too bouncy, that is why I put a layer of steel net and poured a a mixture of rutlands refractory cement mixed with bond and perlite to make it stiff, which did harden the base and was not bouncing. I then placed concrete bricks over that mixture and then laid the 1.5 inch firebricks.
Chach what do you recommend I should do? I can not remove the fire bricks, should I put another insulating material on top of it and put fire bricks over it?

I really appreciate all of you guys criticism and tips. Thank you. Hope you all are safe from what’s going on.

[JRPizza]

I hate to say this but you might be in a place where none of us can do anything other than speculate and or wish we could offer better advice. You either need to do some deconstruction or start documenting your build real well so others can learn from it. I do have a question - are your vertical wall bricks sitting on the rockwool insulation also? We having been saying that material won't support your walls, but if the walls are not on it that problem goes away, but then you are going to be bleeding heat from the walls into your base. Can you give us a sketch of what your cross-section looks like?

[NYFirinci]

[NYFirinci]

I added the photos in the previous post, the fire bricks are not on the insulation. They are standing on the clay bricks.