Design questions

[AJH]

I'm still in the paper planning and researching stage and have a few questions for the group. The attached is kind of what I am thinking.
The yellow is the dome bricks at 4.5" width, the white circle is CalSil blankets at 4", then about 3 inches of verm-crete with some sort of tile or something on the final layer. Red blocks are the concrete blocks and the slab/foundation. I was planning on overhanging the hearth 4" past the concrete blocks using 2x6's on the form so the foundation and hearth would be the same dimensions.

The main question that I have is on the vent/landing/chimney area which is light blue in the attachment. Is 2 full bricks plus a little overhang on the hearth going to be too deep to comfortably work in the oven? It looks like most people have 1.5 bricks on that area.

I have a 3" reveal on the oven to vent transition for a door with the outer arch being 1.5" narrower to hopefully trap the smoke. I can change that if the vent area is too deep or maybe use the thinner side of the bricks on the outer arch...

My foundation and block stand are a little less than what is in the plans, but is probably just due to rounding on the block size (15.625" vs 16" for cement block length).

Anything jumping out that I should address before I start digging out the foundation? I don't want to look back and say that I needed more/less area when it's past the point of no return...

-AJH

[david s]

The total thickness of insulation is personal preference, but 7” is quite a lot. The law of diminishing returns tells us that the extra expense of insulation gives a reduced benefit as it gets thicker, while some also say you can’t have too much insulation.
Vermicrete is cheaper than blanket, but the water it contains (more than a third of its volume) needs to be removed. Just as a pile of sand will remain moist below the surface for months, so will vermicrete. Any layer more than 35mm thick is difficult to dry. Because a lean mix of around 10:1 has about the same insulation value as blanket, it can be a very affective insulation layer while still providing an adequate substrate to render on to. A thicker and richer mix will be stronger, but less insulating and take way longer to dry. You really only need a layer thick enough to even out the lumps and bumps of the blanket layers. Alternatively a 35mm (1.5”) layer can be applied, left for a week to dry and a second layer applied over it, with another week to dry.

The 16” blocks are only 16” when the thickness of a mortar joint is added to their length. The same applies with their heights, 8” when the mortar joint thickness is added. If dry stacking them with masonry adhesive, you’ll lose the thickness of the mortar joint.

The depth or shallowness of the flue gallery will determine the difficulty in managing the oven. My preference is a very shallow gallery with a well funnelled top, leading to a generous (for oven chamber volume) flue diameter.

Your outer decorative arch being narrower than the gallery sides will also make managing the oven mor difficult.

[AJH]

Thanks David.
The vermcrete was probably overkill and I can back it down to just smoothing out the roundness of the dome.
What depth of flue gallery do you like? It looks like 13.5" is what most people go with, do they also have a lip for setting drinks and other random stuff in front of the decorative arch? I can probably get rid of another cement block on the long side if that's true.

[UtahBeehiver]

Don't cut yourself short by removing a block on the long side. It is better to more room than not enough. I actually lipped my outside arch slightly to help funnel the smoke towards the chimney. This was a suggestion from Karangi Dude. Does it make a difference? I am not sure. but it does have to have a radius bigger than the internal arch so you can get you door completely out. You cannot go too thin on 10 to 1 vecrete, it needs a little depth to maintain structure. ie 1.5" or so.

[AJH]

How close is a comfortable distance for the door to the front lip of the hearth? Mine is sitting about 21" in the drawing and I won't be able to quite reach the middle of the oven at that distance. Not sure how often you put your arm that far into the oven either though =)

[david s]

Thanks David.
The vermcrete was probably overkill and I can back it down to just smoothing out the roundness of the dome.
What depth of flue gallery do you like? It looks like 13.5" is what most people go with, do they also have a lip for setting drinks and other random stuff in front of the decorative arch? I can probably get rid of another cement block on the long side if that's true.

My flue gallery is only 130mm (5") not including the outer decorative arch which is another 70mm. But that is achieved by casting a thin gallery and setting it somewhat over the oven mouth to accomodate a 125mm (5') flue pipe. I doubt whether this is achievable if you plan on building it with brick units.

[david s]

"How close is a comfortable distance for the door to the front lip of the hearth? Mine is sitting about 21" in the drawing and I won't be able to quite reach the middle of the oven at that distance. Not sure how often you put your arm that far into the oven either though =)"


This is why large ovens with deep galleries require tools with long handles.

[Sixto]

How close is a comfortable distance for the door to the front lip of the hearth? Mine is sitting about 21" in the drawing and I won't be able to quite reach the middle of the oven at that distance. Not sure how often you put your arm that far into the oven either though =)

I had to build a mock-up of the gallery in cardboard to figure this out. The answer depends on the height of your hearth, how tall you are, how comfortable you are reaching-in, how strong and flexible you are, and whether you are building the oven just for you or will others also be working the oven? https://community.fornobravo.com/for...ge5#post450280

I ended-up building the largest gallery I’ve seen on the forum, but it does NOT do a great job of funneling the smoke upwards for the first 30 minutes when I’m starting the fire. On the other hand, Once I reach pizza temperatures, there’s no more smoke coming out the front. My goal is still to use the gallery as a coal grille, so that’s the price i had to pay. I am 6’-1” tall, 63 years old in fairly good physical shape, My gallery dimensions are: 36" wide, x 18" deep x almost 22" tall at the center, and the distance from the edge of the hearth to the door is 27”. i ended up with about a 6’ horizontal reach to the back edge of the dome, where the 2nd pizza sits. I have NO PROBLEM working the oven with welding gloves and a 4’ turning peel. I do have to get my whole body in the gallery to reach that far… (sometimes I have to close my eyes and hold my breath, though)

After saying all that. If you don’t have a need for a grilling area in front of your oven, I endorse David’s suggestion (and traditional practice) to make the gallery as short as possible front-to back, and the idea of casting the gallery seems like a good way to achieve that. (See Mr Slowhand’s build for a brick/cast gallery example. https://community.fornobravo.com/for...ge4#post450195 ). Some build a custom stainless gallery. If you stay with bricks, a distance around 12” or 18”” from the door to the outside face of your decorative brick or tile arch should do the trick if your slab does not extend much further in front of that. I would not extend the slab for drinks in front, because that’s your working area, which you will want free of clutter, and extra space just makes the pizzas harder to reach. I have about 8” in front of my gallery arch, and I now wish I had built additional space on one side of the gallery, instead of the front.

Keep us posted!

[AJH]

Thanks Sixto, I was hoping you would see this and chime in since your flue galley is way longer than most.
I think I'm going to try and shrink down the front to 1 or 1.5 bricks without much of a lip on the hearth. It looks like Mr Slowhand's has 2 bricks from door to the edge, it's kind of hard to tell. I'm not sure about casting the flue... My brick work will be amature at best, but casting will probably be worse. I like the look of bricking it up to a point that a chimney pipe is fitted to it or just bricking up to the top.

I watched some YouTube videos from TheWoodFiredOvenChef and it looks like his is quite short so that he can reach in and move pans around. I really liked when he was cooking on the Tuscan Grill inside the oven. I'll let the vent area marinate in my noggen a few days while I prep the area that I'm going to dig out for the foundation and hopefully come up with something that I like.

[AJH]

New question:

Has anyone used insulating fire brick under the oven instead of the CalSil board or Vermicrete? I was looking at the specs and it looks similar to the FB board in composition and thermal conductivity.

-AJ

[Sixto]

I used 2 layers of insulating firebrick with offset joints (a little less than 4.5" tall), plus I turned my floor bricks on top of that so they are 4.5" tall also. It seems to be working fine - holding heat without an insulated door, just bricking up the arch, I'm getting around 350f on the morning after making pizza. Enough to cook a roast, but I also want to bake, so I'm working on a thick insulating door. I laid the insulating firebrick as tight as I could with leveling sand/clay, no mortar. I built the dome on top of the insulating fire brick separated by a sheet of newspaper so the dome could move independently if it needed to. The floor bricks are free-floating inside the dome with just leveling sand and a cardboard ring for an expansion gap. No issues crushing the insulating firebrick with the full dome weight on top. I insulated around the dome and firebricks with 2 CF rolls, added 1.5 to 2.5" of perlcrete on top (quite a challenge) and plastered with homebrew on top of the perl-crete. I'm happy with my results so far.

[AJH]

Sweet! Thanks Sixto! I was looking at the cost of the FB CalSil board for insulation and I figure it's about $270 for 2 inches, where as insulating firebrick would a much cheaper option.

Fun facts for you. I was grew up just over the border in River Falls, WI, and my girlfriend is a licensed architect and worked in Maddison, WI for a little bit as an AIT =)

[UtahBeehiver]

Unless you are getting a great deal on insulating bricks (typically 4-5 bucks a piece), CaSi is right in the ball park is not less. K value of insulating FB is 0.15 where as CaSi is 0.05 so CaSi is three times more efficient than insulating FB (as per Engineering Tool Box) If you are on a budget, you can consider p or vcrete but you need twice the thickness vs CaSi. If you have not do loaded the eplans from Forno Bravo, you should and digest. Most questions are answered in the plans. I will move your thread to Pompeii Construction as you start construction. This section gets the most views and traction.

[AJH]

Hmm, I had assumed that the insulating firebrick would be about the same cost as the medium duty firebrick... Might just pour a 4 inch vermicrete layer and bite the bullet on a 2 inch layer of CalSil board on top of that. If I do a layer approach like that, should I use some tile fragments between the hearth and Vcrete or just use that to separate the CalSil from the water in the Vcrete?

I figured I would start a build thread once I break ground and start digging =)

[fox]

Some costings will depend on your location, where I live vermiculite is quite expensive (and a real pain to use) ceramic fibre board is relatively cheap (and is what I use).
Insulating fire bricks come in many temp ratings, the higher the rating the softer the brick however where I live they are really expensive!
I have built the whole gallery with insulating bricks in the past (not the floor) but they are prone to damage.