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Author Topic: Building An Oven  (Read 4415 times)

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Offline D L Bahler

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Building An Oven
« on: February 28, 2017, 12:26:31 pm »
Not quite a timber frame or log building, but it is attached to a log building, and I thought perhaps some of you might be a little interested in this project anyway.

Currently, between gathering sap and boiling it down to make maple syrup, I am building a masonry oven to be used for the baking of breads and other foods.
Since we had an unseasonably warm spell, I took the opportunity to excavate the foundation and get started.

 

  

   

 

After digging the trench 30 inches deep, I then filled it back in with rubble. THis is mostly crushed and broken up concrete blocks. I had a number of blocks that were damaged and chipped and some others that had been exposed to too much heat, so those were all smashed up and tossed don in the trench.

 

 

Then I made a form and capped the rubble off with some concrete to make a nice level surface to build on.

 

  

   

 

Now I've started laying some blocks. THese are recycled block that have a lot of old mortar on them. I tried cleaning some of them off, but that doesn't work very well. SO instead I've decided to lay them up like they are. They won't have nice joints, but thew whole base is going to get plastered or stuccoed anyway so I don't really care. The base will also be capped with a concrete pad, so it doesn't really have to be straight and even or anything.

 

 

I have a whole lot of salvage bricks to use for building the oven itself later on. I was hoping to find some old solid clay soft bricks from some old building, as they can handle the heat of a bake oven. Modern hard brick cannot. A local brick yard happens to have a whole pile of salvaged bricks they said I could have for free. At first I was unsure what they are, thought maybe they were old sand-lime brick due to their color, texture, and the obvious presence of sand. TUrns out, they're old refractory brick, apparently taken out of an old kiln or furnace since they don't have any mortar on them.

 

  

 

I got 580 of the yesterday, today or tomorrow I hope to get 500 more.

Online ljohnsaw

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Re: Building An Oven
« Reply #1 on: February 28, 2017, 12:36:51 pm »
Wow, great build and cool find on the bricks.  Was cement poured down into the footings or just basically on top?  I'm assuming the 30" is for frost heave.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline D L Bahler

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Re: Building An Oven
« Reply #2 on: February 28, 2017, 04:55:45 pm »
THe footer is just a rubble-filled trench. I'll assume a lot of you know about that, but for those that don't, it's an old way of making foundations and is exactly what it sounds like, a trench filled with rubble. A lot of very old buildings, particularly in Europe, are built on foundations like this.
The disadvantage is that dirt will seep back in over time (due to water running through it) and fill the voids between the chunks of rubble. You can prevent this by filling it up with fine sand along the way, or slow it down considerably by lining your trench with some kind of membrane, or like you say you can even pour in very wet concrete.
But for this application it's not super vital.

The 30" is to get well below the frost line. The cabin beside it has essentially the exact same type of foundation, only the trench was a bit wider, the rubble a bit finer (and the top half or so exclusively stone) and the depth went all the way down to 40 inches at its shallowest point, with a drainage tile buried underneath it.

For the oven foundation, the concrete is only above the grade line, and not as a fill between the rubble or anything like that. It's just there to give me a nice little cap to make things level, square, and even for laying block.

By the way, the image here is basically the design I'm using, with a few modifications to reflect the materials I am using (The profile of my bricks, primarily)

 

 

This is a German design, with a rear exhaust port (rather than having the front arch serve as both the air intake and exhaust outlet per the common Roman design) that snakes back out to the front.
I won't have it turn to the side to go to a chimney, but it will just come out the front and then draft up into a collection hood.
So the final oven would look kind of like this:

 

 

Primary differences would be that I'll have an area underneath the oven to put firewood, and I may not plaster over the upper section.


Offline D L Bahler

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Re: Building An Oven
« Reply #3 on: February 28, 2017, 05:01:10 pm »
Forgot to mention,

The dimensions of the base will be 6'X8'
The dimensions of the interior of the oven will be 4'X6'

The height of the side walls will be about 10 1/2" in the front, 9" in the back (the floor slopes upward toward the back at about a 2% grade)
The arch will be based on a 48" radius circle, so will have a rise of about 6" making the center of the oven about 16 1/2" above the floor.

Online ljohnsaw

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Re: Building An Oven
« Reply #4 on: February 28, 2017, 07:39:33 pm »
So the exhaust / smoke will be coming out the center port on the top/front?  What is the reason to go to all that trouble and not just have a chimney at the back of the oven?  Will there be a damper on the front port to control the fire some how?
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline D L Bahler

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Re: Building An Oven
« Reply #5 on: February 28, 2017, 11:21:01 pm »
It makes it convenient for controlling the exhaust, I believe is the primary purpose.
Though I admit I'm not entirely sure why they did it this way all the time. THe picture of the old oven with two exhaust ports, I don't see any kind of damper or anything. But my belief tends to be that the people who made these designs were experts at building ovens, so I tend to think they probably did things their way for a reason.

It is important for baking to shut off the exhaust port when the fire is scooped out, so your heat doesn't all escape out the top of your oven. SO maybe that's it, put the exhaust ports right out front so it's easy to cap them off.

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Re: Building An Oven
« Reply #6 on: February 28, 2017, 11:48:30 pm »
It is important for baking to shut off the exhaust port when the fire is scooped out, so your heat doesn't all escape out the top of your oven. SO maybe that's it, put the exhaust ports right out front so it's easy to cap them off.
Makes sense.  I didn't think about that because the few restaurants I've seen using wood fired brick ovens keep the fire going the whole time (since they are cooking for several hours).
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline D L Bahler

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Re: Building An Oven
« Reply #7 on: March 01, 2017, 12:10:48 am »
This is a bake oven, operated by storing a lot of heat in the bricks. You build a very hot fire and get the bricks smoking hot, like 900 degrees. Then after things even out a bit (you can bake some thin crust pizzas at first at the super high temps) you stick bread in the oven, and the heat stored in the brick does the cooking. It's an ancient idea, been around as long as civilization itself, though the design of most bread ovens was developed by the Romans from a Greek pattern, which itself probably came from Egypt or Mesopotamia

We want like 400-600 degrees for bread. When it drops below that, you can cook other things, like a roast or some pies or things like that. This oven once built should be able to hold a good baking temperature for a few days due to the thick layer of sand insulation between the oven bricks and the outer structure.

This oven is a German design. The Roman Oven, which may be either vaulted or domed, has a front opening carefully sized to operate as both air inlet and exhaust. There is often a hood built onto the front of the oven so that the smoke drafts out into a sort of chimney. Central Europeans, from one of the German-speaking countries, developed the idea a little further by moving the exhaust to the rear of the oven. This draws the heat of the fire through the oven, and warms it quicker and more evenly while burning the fuel more efficiently. 

I would suspect the old German ovens vented the smoke out the front so that it could be vented into the middle of the oven house and used for smoking meat and cheese hung up in the rafters. Another possibility is that the design predates the invention of the Chimney. It's also possible that bringing the smoke through a crooked passage that winds back up to the front also helps to capture some more of the heat before it pours out of the exhaust.

Note in the drawing shown, the center hole above the door is just an access door for cleaning. The smoke itself turns and vents out through a chimney stack on the side.

In the old oven pictured there are two small holes above the oven door where the smoke comes out. The area above the oven door and above these two holes are stained black from the smoke. This shows the person using this oven hasn't always fired it the best. When firing the German style oven, you need to heavily restrict the air intake at first, or the smoke will backdraft out the door until the exhaust ports have gotten hot enough to create a draft. Obviously this oven has seen a lot of backdraft of smoke out the oven door during the early stages of firing (This oven is located at a museum in Switzerland where it is sometimes used to make good bread. They also have a much larger commercial style oven of the same basic design at this museum.

Offline nativewolf

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Re: Building An Oven
« Reply #8 on: March 01, 2017, 02:51:51 pm »
Very nice score on the 1000+ refractory brick!  That's a huge monetary + on the overall project.

Great project

Online ljohnsaw

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Re: Building An Oven
« Reply #9 on: March 01, 2017, 03:21:22 pm »
So is refractory brick like firebrick?  Firebrick is insulating in that heat does not pass through it.  Does refractory brick heat up and pass heat (into your sand) so the oven can "store" the heat for cooking?
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline D L Bahler

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Re: Building An Oven
« Reply #10 on: March 01, 2017, 03:40:34 pm »
Refractory and fire brick are the same, though there are many different types of refractory, usually represented by their hardness.

Soft refractory brick is an insulating material, what you would use in pottery kilns and other small hot things that need to insulate very well.
Hard refractory brick is heat-resistant material that may not necessarily insulate as well, due to the fact it is much denser, but it can put up with a tremendous amount of heat, as well as being rugged and durable.
So hard refractory brick will thermally act much like solid clay brick, but the silica mixed into the clay means that it won't crumble and break down from all the heat.

A soft brick contains a lot more air (air is the primary insulation of just about nay system, the key is to isolate it in tiny pockets that can't circulate) so it doesn't store heat or transfer it very well. Hard brick will heat up and can transfer some of that heat, but the heat on the cold side of the brick isn't going to be as extreme as the heat of the fire on the other side. The thin firebrick used in fireplaces is often hard brick. It's not actually there to insulate, per se, but rather it's there to shield the more fragile clay brick of the chimney/hearth from the flash heat of the fire. A fireplace relies more on reflection than it does on insulation. THe firebrick reflects the more intense heat of the fire back out, while slowly absorbing some of that heat.

So in this application, we are storing the heat in the bricks themselves. The insulation around the brick is to slow down the passage of heat from the oven brick out into the rest of the oven structure or into the air. A lot of backyard pizza ovens just consist of a vault or dome and that's it, maybe a light layer of plaster over the outside to add a slight amount of insulation. The brick gets very hot, and radiates much of the heat back inside of the oven, but also loses a great deal out into the air. That's OK for home use, because you're not really planning on using it all day anyway.
This is a commercial oven where we want to fire it and be able to use it pretty much all day without having to refire it. So we try to ensure that the only heat loss is the heat used in the chemical process of cooking, and we do that by thoroughly insulating the whole oven. The finished oven will be a huge block 6 X 8 X about 4 feet with only a small amount of that volume occupied by the baking chamber.
This oven will require a firing time of a couple of hours due to its size, but should be able to hold baking temperatures for 2 or 3 days, or much longer with a few small fires between batches. An oven of this size can bake close to 2000 loaves of bread in a week if it's running full time. We don't intend to put out anywhere near that volume, at least not yet.




Offline Czech_Made

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Re: Building An Oven
« Reply #11 on: March 02, 2017, 08:51:48 am »
Following

Offline D L Bahler

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Re: Building An Oven
« Reply #12 on: March 02, 2017, 07:46:34 pm »
More or less finished the pedestal this afternoon

As I mentioned earlier, the blocks are night laid even and nice. These blocks are recycled and have old mortar on them (also, they are from the 50's and are considerably stronger and heavier than most modern block) I borrowed a technique that I've often seen used in tropical countries, where locks are laid rough and then the whole structure plastered over -I did this because the nature of these recycled blocks meant laying them 'proper' was impractical. The rough laying job gives the stucco more texture to key into, making it stronger. Also I laid them up without mortaring the vertical joints, these will be filled by the stucco (I'm using mortar mix as the base coat for the stucco so it will actually provide some structural strength)

There is also a central row of blocks you can see in the middle. These are just dry laid for now. They will be stuccoed over and filled with concrete to make a solid support for the center of the reinforced concrete pad that will sit atop the block pedestal.

So the next step is to coat the blocks on both sides with a base coat of stucco, I won't worry about the finish coat until everything else is done.

 

  

   

   

   

 


The little bit of stucco at the corner is just the left over mortar I had after laying the blocks

NOTE

I do know how to lay blocks proper, I promise. You can look at the foundation wall of the cabin in te background if you don't believe me! (which is also intended to be stuccoed some day)

Next steps:
-Stucco the walls
-Fill the center wall and the corners with concrete
-Stuff the empty block cavities with paper
-Form up and pour a 4" thick concrete pad on top of the pedestal

I may also put a brick arch on the front opening of the pedestal, just for decoration. It's not really necessary for structural reasons, but it would make it look nicer.

Hopefully next week, we'll get to work on the actual oven itself!

Offline badger1

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Re: Building An Oven
« Reply #13 on: March 03, 2017, 07:59:33 am »
New poster, but have been watching this thread closely as its something I definitely want to do myself. Thanks for the great pictures its very helpful! I've purchased several books about masonry (Latest was by McRaven) and have been "studying" a bit. Curious as to how you will tie this into the cabin/structure. Once you have the cinder blocks filled with concrete and the top pad poured how you will bring it into the cabin at the same level as the inside finished floor. Will there be a concrete hearth that is level with the inside cabin floor?

My project will be in NW WI or Northern MN and thus I will need to go deeper for frost footings, but if you have the chimney base independent of the cabin footings, and then "tied into" the cabin flush with the floor is there any potential for both separate structures to move independently with frost? Would you see gaps between the cabin wall and the fireplace? Although I suppose in theory if both the cabin footings and the chimney footings are deep enough to not be affected by frost, neither should move, correct?

Also will be interested to see how you continue the chimney up to, and through the roof or eves with associated flashing etc.

Please continue to post plenty of great pictures, again it's very helpful!
Contact me via PM, willing to help with projects for more experience

Offline D L Bahler

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Re: Building An Oven
« Reply #14 on: March 03, 2017, 02:01:56 pm »
I won't be tying the oven structure directly into the cabin, at least not to the cabin wall. I plan to extend the roof over a short wall that will be built atop the oven superstructure and on small foundation piers in front of the oven, making a little room on the side of the cabin.

I also won't have a chimney, but I'll just have two smoke holes on the front and a large hood above the oven.

Offline D L Bahler

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Re: Building An Oven
« Reply #15 on: March 03, 2017, 03:11:48 pm »
Working on framing the supports for pouring the concrete. Need to run into town and grob some supplies (more 2x4's, rebar, etc) so thought I'd just put a quick update up

I framed a 'floor' out of plywood and 2x4's that's more than strong enough to support the weight of the pour. Originally the plan was to make it removable so I could take it out after the concrete cured, but I've decided to put some tar paper over the top before pouring in the concrete, and just leave it there for a little added strength, even though I know it'll be redundant. Not much of the oven's actually weight will bear down on the reinforced concrete pad, so I'm probably overdoing it a little bit but who cares?

I've also decided that, rather than making an arch in the lower opening, I'll leave the wood supports there, and trim the opening with wood after everything is done to make it look nicer.
 

  

 

Offline D L Bahler

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Re: Building An Oven
« Reply #16 on: March 03, 2017, 07:54:06 pm »
Got formed up and almost ready for concrete, just have to cut the rebar and wire and lay it in.

 

  

  

  

  

 

The tar paper will isolate the wood supports underneath from the concrete, so it won't make it rot out. It also is there to stop the concrete running down through the various cracks, gaps, holes, etc.


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Re: Building An Oven
« Reply #17 on: March 03, 2017, 11:42:36 pm »
The tar paper will isolate the wood supports underneath from the concrete, so it won't make it rot out. It also is there to stop the concrete running down through the various cracks, gaps, holes, etc.

Will you be poking holes in the paper for the concrete to makes its way down inside the cement block?  Wondering how you are going to tie the slab to the walls.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline D L Bahler

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Re: Building An Oven
« Reply #18 on: March 04, 2017, 01:30:41 am »
Not particularly worried about tying the slab down. The slab itself will weigh about a ton, and will have maybe 3 1/2 tons of oven on top of it (1000 bricks = 5000 pounds, more or less, plus the sand insulating barrier between the oven and the outer walls) , plus a few hundred more pounds from the wall and extended roof section on top of that. I don't expect it will be going anywhere. 

The oven itself will also not be tied down to the slab in any way, in fact the main bricks of the cooking chamber will be dry laid (meaning I have to grind or cut down the bricks forming the arch so they fit together without mortar). I plan on having an inch of sand between the slab and the oven floor (I don't want the concrete to get hot. Concrete tends to explode when it gets too hot) And the oven floor bricks will just lay on top of the sand. The whole hot structure is dry laid so it can stand repeated heating and cooling cycles without tearing itself apart over time. This is actually (or at least was) standard practice for things like this, or most masonry constructions that are built to get very hot.

As another note, after studying on the topic of reinforcing the concrete (with the numbers listed, you begin to understand why it needs to be so well reinforced) I've decided to go with 2 layers of re-mesh within the c. 4" slab, rather than using re-bar.

The plan, right now, is to try and mix up and pour the concrete tomorrow afternoon, and hopefully get to building the oven structure Monday or Tuesday, after the concrete has had a few days to cure.

Offline D L Bahler

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Re: Building An Oven
« Reply #19 on: March 04, 2017, 01:37:04 am »
I should mention along with those numbers,

There won't be very much weight at all bearing on the center of the slab, just the weight of the oven floor. The oven structure itself will all be withing a few inches of the block (THe oven, for example, is 4 feet wide on the inside, while the pedestal is 6 feet wide. The blocks are 8" wide, leaving 4 inches between the edge of the block wall and the inside of the oven. The bricks are 3 1/4 inches wide [I think, maybe they're 3 3/4] so that means there's only about 3/4 inch from the blocks to the oven. So the slab doesn't have to bear very much weight, really, unsupported)