Warped Firebrick

[Gulf]

The confusion may be all my fault. What I am calling "IFB" (insulatng fire brick) are the brick you already have. The light porous (possibly pumice) brick that I see in your pics and on the Menard's link. The Vogelzang FB-1 brick are what I am calling "insulating firebrick" based soley on their weight and appearance. The only extra IFB splits that you will need are the ones that will go under the dome should you choose to do that.

When I say IFB, I meant the new ones that would go on top of the first ones.

You don't don't need insulating firebrick on top of the ones already installed. You need dense firebrick splits to cover and protect the soft IFB floor.

I'll see what that person recommends for IFBs.

You might want to get back with the forum before you buy " what that person recommends ". Get a material data sheet pics etc.

Like I said, my thought would be to cut the IFBs to fit as closely to the wall, then fill the space that was left with the cob mix.

That would probably be just fine. But, you may want to place a strip of cardboard next to the dome wall. It will later burn out and act as an expansion joint that will fill with ash. Dense firebrick won't shrink, they will expand when heated. I'm not sure if you know already, but the dense firebrick won't be near as easy to cut as IFB.

[watchthenanacrossing]

Okay, yea I understand what you mean by IFBs now that I'm doing more research. I had that mixed around. I'm just gonna cut into one and see how it goes, then decide if I want to continue that way.

Do you know where to purchase dense firebrick online? I've been searching and not coming across anything that would work.

[Gulf]

Have you searched for local lumber and brickyards in your area? The ones that sell sell to local bricklayers and contractors?

[watchthenanacrossing]

I've started searching, but I live rurally so there's not a lot of options around me.

[watchthenanacrossing]

So I was looking at the oven and did find a crack that has formed, so it looks like I'm starting over. A little heartache, but at least I can get it proper now.

What would be the best insulation to go in between the firebrick and concrete?

[Gulf]

Well I hope you haven't started any knee jerk demoing just yet! All clay ovens will develope cracks. All masonry ovens will develope cracks. All cast ovens will develope cracks. You can rebuild this thing as many times as you want. You're still going to have to live with cracks. Don't let a crack alone cause you to start over!

[Gulf]

Your decision should also be determined by what you really want out of your oven. A couple of flashed cooked pizzas is one thing. Baking bread (and how many loaves) is the other extreme. Then, there is are the "betwixt and betweens". I'm partial to the latter. I got into wood fired cooking a few years ago due to frequent power outages and wanting to be able to cook off of the grid should the need arised. It has several times since. I like pizza. But, I like being able to throw a few loaves of bread in the oven the next day. I also like being able to put a roast in the oven the day after that.

Look at your needs for the oven. Decide what they are. Then we will proceed from there .

[watchthenanacrossing]

Again, miscommunication on my part. I meant there's a hairline crack in the slab that's developed, so I'm not gonna risk it and just start over.

The way I want to use the oven sounds similar to how you use your's. It'll be used as an all-around oven for pizzas, breads, meats, bakes, etc. I have the same mindset - something off grid that I can use as more of my home oven. I want to cook in it one night and then use the heat of the oven to make something the next morning. I'll also use it to cook things overnight.

So my first thought is to put a layer of insulated brick on top of the slab, then put a firebrick layer for the floor on top of those. The dome will be formed around the top layer of firebrick, so it will only be sitting on the insulated bricks. Would that be enough to hold the heat back from the slab, or should I extend the second layer of firebrick so all of the dome sits on both layers?

Or should I be thinking a different route?

[Gulf]

Yes, for retained heat cooking, you will want to think about a different route. More insution and a thicker cooking surface to start. I would really like for you to download the very affordable Pompeii Brick Oven eBook V2.0. 3 bucks max but, you can name your own price all the way down to free. Though you are wanting to build a cob/clay oven, there is some good information in there concerning the oven stand, structural hearth and some affordable insulations used under and around the cooking chamber of a wood fired oven. The eBook (in pdf.) is a very good starting place to help understand what is needed to build an efficient oven. Imo there have since been some improvements made in insulation, elevation, drainage, and weather protection recommendations.

This Pizza Oven Glossary may help our miscommunications lol. The glossary will define some of the better insulations (also some that are comparable based on availability) that we will discuss later. Please look at both the download, the glossary, and some of the documented builds on the site. You will also find some "home brew "cast ovens in here that are an affordable option and will hold up al lot longer over time than cob imo.

If you do your research, then ask questions before you start each step, there will be no other redos, andI think that you will end up with the perfect oven for your needs.

[watchthenanacrossing]

Sounds good, I'll check them out tomorrow and come up with a better game plan. I just quickly checked out the home brew cast oven, and I like that look. Appreciate all the help and direction.

[watchthenanacrossing]

Alright, here we go. I like the homebrew cast ovens and feel that would probably fit best for how I'll be cooking. I already have a lot of questions as I'm making the plans, naturally, so I'll just start with the hearth cause that'll be the first step.

For the hearth, I'd like to go with a Super Isol board for quicker installation and better efficiency. I have the structural support (3 1/2" concrete slab) already in place from before. I feel a super isol board with a 2" thickness would be sufficient. Should the board be under all the layers of the oven, or does it just need to be under the dome (the 1st layer)? I see in the plans I downloaded that it just needs to be under the dome, and the insulation layers of the dome can sit on the concrete slab. I feel that's the same mistake I made before.

I guess another question to help move forward would be the number of layers that would be sufficient for my cooking. I want to be able to hold the heat in well for prolonged cooking. Tell me if this is overkill:
Layer 1 - Sand, cement, hydrated lime, fireclay, fibers mix
Layer 2 - Vermiculite, concrete mix
Layer 3 - Ceramic blanket
Layer 4 - Another vermiculite/concrete mix layer
Layer 5 - Smooth finish (not sure of material but would like that look)

For underneath the oven, would a FB board also be good to put in between the insulating hearth (super isol board) and the oven floor? Or would placing the firebrick floor on top of the isol board be sufficient?

[Gulf]

This is a cross section diagram of my oven. It's not a cast, but the basic theory is the same. The entire cooking cooking chamber should be coconoed in insulation. The cooking chamber is a heat bank that stores the heat from the fire for later use So all of it is insulated from anything that would rob it of heat.. I hope this gives you some idea of the basics design. david s has made many comments on several threads involving homebrew cast ovens. Most of your answers are probably documented in those threads.

[watchthenanacrossing]

Yea that answers these first questions. I see your insulation layers wrap around the hearth and can rest on the concrete. Also, you have both the vermicrete and calsil as insulation below the floor - the double insulation I was wondering. What's the difference between alumina silica and calcium silicate boards?

I'll look into that other thread to see about the layers for the chamber.