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.
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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.
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Then I made a form and capped the rubble off with some concrete to make a nice level surface to build on.
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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.
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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.
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I got 580 of the yesterday, today or tomorrow I hope to get 500 more.
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.
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)
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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:
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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.
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.
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?
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.
Quote from: D L Bahler on February 28, 2017, 11:21:01 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).
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.
Very nice score on the 1000+ refractory brick! That's a huge monetary + on the overall project.
Great project
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?
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.
Following
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.
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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!
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!
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.
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.
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Got formed up and almost ready for concrete, just have to cut the rebar and wire and lay it in.
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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.
Quote from: D L Bahler on March 03, 2017, 07:54:06 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.
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.
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)
Quote from: D L Bahler 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.
Well, I come from earthquake central :D I was thinking laterally support - keying the slab into the walls so it don't slide off in a shake or such. My floor on my cabin will be between concrete filled, rebar reinforced block yet I still had to run my flooring at a 45° angle.
Ah yes, earthquakes.
We've had 2 in my lifetime in central Indiana, both around a 4
Supposedly the New Madrid fault is overdue for big one, like 8+, but that depends on who you ask. Other people say it will never shake like that again. (Legend has it the last time it shook, it rang the church bells in Boston, which is like 500 miles away or probably even more than that)
Either way, earthquakes are an extreme rarity in Indiana, and if we ever do get a big one, most say it will be a REALLY big one that nothing at all here is built for.
Biggest earthquake I ever felt was in Haiti (not the bad one that destroyed Port au Prince, but a smaller quake that rumbled the city some time later) I think it was like just shy of 5, so again not real big.
If I were building for earthquake, I'd probably borrow techniques from the most successful earthquake engineering society in history, The Byzantines. I always loved the story about the walls of Constantinople (Istanbul, if you must) The Turks blew a massive hole in them when they took the city. In modern times, the Turkish government decided to repair the wall but didn't use the same techniques that the Byzantines had used originally, they just made it *look* the same. The city was promptly hit by a large earthquake; the repairs crumbled into ruin, while the 500+ year old Byzantine walls were unaffected.
But for this project in good old boring, stable, Indiana I'm not concerned about lateral stiffness at all, because I don't expect the earth to shake in any significant way any time soon (Unless the good Lord should return, and then I won't be too concerned with the state of my oven!)
Any insulation to go under the oven? So when you heat it up, it does not dissipated down?
There will be a layer of sand between the concrete and the bricks of the oven floor for this reason. This sand will be about 1 inch deep in front, 2 1/2 inch deep in back. It serves the double purpose of insulating and also establishing the proper slope for the floor.
Just got done mixing and pouring all the concrete, and taking a little break while it sets up enough for me to finish it.
Toting, mixing, and pouring 40 60-pound bags of concrete with just a wheelbarrow, a hoe, and a shovel (also, I had to tote the water about 200-300 feet in five gallon buckets) all by myself made me just a little tired.
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Let the fun begin...
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Forgot to take a picture to show how I did the reinforcement. There are two layers of mesh, one about 3/4" from the bottom, the other about 1-2 inches above it, staggered so the wire doesn't line up.
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In hindsight I should have drilled weep holes through the plywood (and tar paper) to let the excess water run out the bottom. Usually when you pour concrete, you have gravel underneath it and the excess water escapes easily. I neglected to consider this, so I ended up with a lot of water coming to the top. That also means that the whole mass of concrete shrinks a very small amount as it sheds the water, So i had to go back and add more concrete as it shrunk.
Started working on the body of the oven this evening, laid up one of the outside walls (because I won't be able to access it once the oven is built due to its closeness to the cabin) and went ahead and used up the rest of the mortar I had mixed up while I was at it.
Then I dry laid the bricks for the walls of the oven chamber itself.
You can see form of the oven starting to take shape. There is about 4 1/2 inches along the sides between the oven chamber bricks and the bricks of the out er wall. The next step is going to be to fill this area with sand to insulate the oven and also buttress the oven walls. The arches, also dry laid, will lay on top of the walls, and will naturally want to press outward. The arches need the added strength of the sand and the mortared outer walls to keep from toppling over. There will also be steel plates on the sides of the oven connected with reinforcing bars that pass through the structure just above the top of the oven chamber to help hold the walls against spreading.
Before I fill the void with sand, I'm going to render the outside of the dry laid bricks with mud (not clay, just ordinary mud) This makes it a little stronger, and helps with the thermal properties quite a bit.
The actual chamber ended up a little larger than the preliminary design, as a consequence of the size of the bricks. The basic plan was 4x8, but the actual intention was to make it whatever the size of the bricks dictated nearest those dimensions. I wanted to do as little cutting as possible.
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So now the agenda looks like:
-Render the outside of the oven chamber walls with mud
-Finish laying up the outer structural walls
-Fill the voids with sand
-Lay up the arches
-Attach reinforcing rods and plates to structure while laying the arches.
-Render the top of the arch with mud.
-Build the exhaust chambers
-Fill the space on top of the oven with more sand
-Cover the top of the oven structure with something? Maybe just a lime cement render, maybe nothing at all...
-Extend the cabin roof over the oven
-(Some later date) enclose the oven in an all-weather room, complete with concrete floor
I should note,
The original German plans I'm using as a basis use 2 sets of vertical steel plates on the outside of the oven to reinforce the walls against the spreading of the arches. Those plates are attached to their counterparts on the opposite side of the oven via long steel rods, one set passing above the oven and the other passing through the sand-filled area directly beneath the oven floor.
I plan to do it slightly differently. I'll have steel rods that pass above the oven, much the same.
Instead of a second set of rods below the oven floor, I intend to use large tapcon screws to anchor to the concrete pad
Another Progress Update
Today I laid up more of the outside walls, and also framed the two openings for the main oven door (two openings, because it goes through two different walls)
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Here you can see the support for the first opening in the oven chamber. I used two pieces of angle iron, one on either side of the wall. Later on I plan to weld a steel plate across them to tie them together so they can't fall out.
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You can also see the three pieces of thin firebrick laid in the opening, mortared down to the brick wall. These will be at the same height as the front of the oven floor (the rear will be about 1 1/2" higher, about a 2% slope) Which will actually allow for about 2" of sand under the brick of the floor.
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I then laid up the front wall of the outer structure, and supported the bricks above the opening the same way.
You'll notice that the angle iron on the inside wall is longer than that on the outside wall. There being no mortar between the bricks of the inner structure, it's necessary the steel be under all of the bricks on this section of the wall (4') so they all sit at the same height. On the other wall, the difference can be made up with the mortar so I didn't need (or want, because it makes a weaker joint) as long an iron.
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I put a scratch coat of the cement from the mortar over the front angle iron to make it blend in to the brick a little better. I doubt it will stay very well (who knows though, anyone whose done brick or block on concrete work knows how hard it can be to get cement off of your metal tools a day or two later) but in the mean time, I think it looks better
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The oven door will be attached to the angle iron above the opening and hinge upward. I'll probably tap some kind of locking mechanism into the brick on either side, but the basic design of the door is to use its own weight to keep it shut.
The hinge straps will bolt to the angle iron, with a heavy bolt that passes through both pieces of metal, and is secured with a locking nut on the inside.
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Like the buiding progress.
Very nice, I am watching with interest!
What is the benefit of dry stacking the interior wall?
Dry stacking allows the brick to expand and contact freely with the drastic changes in temperature (like a 900 degree range of difference) without having to worry about eventual mortar failure and fracture.
I'd imagine even refractory mortar would have a different expansion coefficient than the bricks themselves, so these heating and cooling cycles would eventually cause the mortar to degrade and break down (not necessarily because it can't put up with the heat, but because the expanding and contracting bricks would eventually pull it apart)
It's pretty common practice to lay ovens, furnaces, etc. dry.
We're relying in this case on the outer walls to provide most of the necessary structural strength as far as lateral forces are concerned, so there's really no reason why the oven chamber should be mortared together.
That makes sense. Do you ever see any issues with the sand pushing the bricks inward?
There's not really enough sand to do that here. All in all, there will be a bit under a ton of sand to fill the wall cavities and the floor. So that's spread out around two 6 foot walls and a 4 foot wall. I havent calculated, but I'd imagine there to be only a couple psi of force against the walls from the sand. What's more of a concern is that the bricks will be forced outward by the arches, especially as weight is applied on top of them. This same weight will also press down on the bricks in the walls and create more friction between them.
Last night I laid out the arch template (don't have any pictures yet, sorry) To figure out how many bricks exactly it would take to build each arch, and how much each would have to be tapered to fit securely without using mortar. Turns out, each arch (there will be 9 arches total) will use 21 bricks (the number has to be odd, because you need to have a key at the top of an arch) and each brick will need to be tapered 3/16". TO do this, I will use a diamond grinding wheel to carefully shape each brick -all 189 of them- plus the 18 bricks that will sit on top of the walls to hold the arch bricks at the proper angle.
Tonight I laid most of the remainder of the outside walls up to the height of the cross ties. There's still a few bricks to lay on the back, but I'll worry about that later.
I need to be getting a ton of sand shortly. The walls need filled in before I can lay up the arches, or else there will be nothing to hold them together.
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I had a fun experience yesterday on the way to a job. Some tire shops, it seems, can't be trusted to torque lug nuts tight enough on a ton truck. While driving down the high way, the truck began to vibrate badly. I was getting ready to pull off on a side road when the tire exploded. As you can see, 4 of the lug bolts sheared off and the rim is trashed (want you can't see is the back side. where the rim deformed upon impact with the road)
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I really appreciate you taking the time to answer my questions. On the to do list to build something like this someday in the fairly near future! Really enjoying your photos. Thanks again! That's a little scary on the tire....
How high will the inside of the oven be? Where you have the all-thread, is that the height it will be in the final build? Will that pass over the vaulted inner oven? I believe you mentioned that you will coat the out side of the inner wall with mud (dirt, not mortar). Still planning on doing that? Looking pretty tight to get in there to do that now!
After building up the floor, the inside walls will be 9 inches tall in the front, 7 1/2" in the back. The arch is 7" tall, so the high point of the oven chamber is 16"
The threaded rod sits just over the top of the arch bricks (so not through the baking chamber) You can see the approximate height of the baking chamber arches if you look at the end walls of the inner chamber.
There is 4 1/2' between the two walls, there's plenty of room to stick a hand in there to mud the walls, though I'm not sure if the vertical walls will get i, because they don't really need it. Heat loss is going to primarily be upward, so I think it's more important to seal the top of the oven.
I carry a torque wench in my one ton plow truck and check the wheels because i had a lot of problems with the wheels this year :(
While laying in bed last night I had a revelation.
I was thinking about the infill between the walls, and realized that for this purpose, dirt is just as good as sand. I have lots of dirt, a whole pile from digging the foundation trenches. So I filled the walls up with dirt, and also filled up the floor cavity, being careful to make it even as I could, and to break up any clumps I encountered.
Using dirt in the floor instead of sand does mean I have to be a lot more careful when setting the floor bricks and later when setting the arches. I've got to put pieces of plywood over the bricks so I don't compact the dirt and push it around too much. But once that's all done, I would think it should be OK.
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A couple things to point out:
Dirt moves around a lot more than sand when you're working with it, due to the much smaller particle size. So you've got to be real careful when working with the floor like this. But once the bricks are all in, it's pretty secure and stable. Time will tell if this was a good idea or not.
You can also pretty clearly see the slope of the floor in some of these pictures. I Put a 2% grade on the floor because my plans said to do so. I imagine a few things thi will do:
Encourage the heat and smoke to draft backward, while helping to heat the floor evenly from front to back
Aid in scooping out the ash
Aid in loading and unloading the oven
There is a row of bricks in the rear of the oven you may have noticed are stacked atop the floor on their sides. there are 19 rows of bricks from front to back, and about 3/4" space between the 19th row and the rear wall (a consequence of dry stacking bricks whose dimensions are designed to account for mortar joints) This is too big a gap to simply leave, but too small to be able to cut clean bricks to fit in the space very well. I decided to put these bricks in like this to cover the gap, because the back foot or so of the oven is dead space anyway. I figured this would help airflow somewhat, and also cut off what is normally the dead corner of an oven of this design, the rear bottom corner where there's not good airflow.
I'm considering grinding an angle on their faces to improve circulation in the rear a little more.
I put up the first arch tonight. I experimented around a bit to determine exactly how I want to support the arches, etc.
The picture here are actually of an early trial. It worked well enough, but I decided I wanted a more secure means of support so I took it down and redid it.
I ended up placing a brick to bridge the gap between the arch feet and the outer walls, since none of the other methods seemed to be satisfactory in this case.
Also not seen here iss an important step when laying up dry arches that I forgot (my battery died so I don't have any pictures of the final arch) That is to rub the top of the arch with dirt (or in this case, dirt mixed with some sand) or mortar or whatever is handy to fill in the gaps and imperfections. (The other option is to be incredibly precise grinding the angles on your bricks, but that's VERY difficult. If you rub a little something over it all to fill in the gaps you have a little room for error)
If you don't do this, the arch will have a tendency to go lopsided or even collapse.
If it wasn't currently below freezing, I would have rubbed it over with mud instead, but that will have to wait until later.
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You can see the slip form I'm using to put the arches together. I'm taking advantage of the sloped floor. The two 2x4's rest on a sheet of plywood in the rear of the oven and on a 2x4 in the front (accounting for the 1 1/2" of difference in height) When I want to remove the form from under a completed arch, I knock out the support 2x4 in front which allows the arch support to fall down and be removed. THe first arch is the most difficult to do this way, since the 2x4's don't drop down any in the very rear.
A few notes on making the arches for those following with interest of making their own oven:
It's easiest to grind the angle on just one side of the brick. Then alternate each brick as you lay it in (so the angle ground sides butt up against each other, unground sides butt, etc). It's hard to keep 2 faces flat when you grind the bricks down like this (I'm using a diamond grinding wheel, it makes a lot of dust but is pretty slick.)
If you don't think you can do a good job grinding, you can just lay them in without grinding, and pack refractory mortar in the wedged opening. The disadvantage of this is you have to wait for the mortar to set before you can move on to the next arch.
Just to reiterate, when you lay an arch dry and before you remove the form, rub it with dirt or fine sand (or a mixture of both) a smear it over with a slip or mortar mixture of some kind to fill in gaps and imperfections. Unless you make a check gauge and carefully craft each individual brick there are going to be imperfections and inconsistencies (or if you're lucky, you could get your hands on some arch or wedge bricks and then this step is unnecessary). When the support is removed the arch will seek to balance its forces within itself. If imperfections are present, it will average them out meaning the arch will go lopsided, and it will be 'wobbly' which means it might fall apart eventually. If the imperfections are too bad, it will fall apart right away. So filling in the gaps thoroughly makes it stable.
If I remove the template and the arch moves AT ALL, then I'm going to take it apart and redo it.
You really only need (and want) a flat segmental arch for an oven. This arch has 7" of rise over a 49" width, it's based on a 48" radius circle. That's actually more rise than I need for stability, I could get by with like 3 inches of rise to support the structure if I wanted to, but I chose to build an oven with shorter walls and a higher arch mostly because it looks better (even though nobody but me will hardly ever see the arches once it's all done)
The taller you make an arch, the harder it is to support.
Actually wehn I was taking one of my trial arches apart, a brick or two removed it fell down and the tops of the remaining bridges wedged themselves together to form a very strong and stable arch that had maybe 1" or so of rise.
When assembling the arches, make sure to firmly seat each brick as you lay it in, otherwise the arch will shift when you remove the supports. I take my masonry hammer and tap each brick several times until it seems to be firmly seated on the brick below it. Also take care to align each brick in every other direction as you seat it. Once the key is in place, and especially once the form is removed, it is very hard to adjust and move anything.
For these arches, I'm trying to make my keys to where they will drop in about halfway, and then need tapped in with the hammer the rest of the way. This way any slack that's left in the arch is taken out. This also will lift the arch above the form a little bit, which in turn means the top edges are being forced open (or the bottom edges being forced together) aim for consistency in how much the key drops in before being driven and how much wedge they have in them, otherwise your arches will not line up with each other.
This is a fascinating project. Thanks so much for the many pictures and the detailed description.
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Here are some pictures of the arch that I kept. You can see the support for the arch cleats, and the dirt and sand I smeared in the top
It's been a little while since I've been able to get any work done on the oven, but the day I found some time to pick up another load of bricks and to get to work on a couple more arches. The first Arch I laid today needed to have the vent holes for the smoke cut into it, so I just ground release in a couple sets of mating bricks to form the smoke holes. Other than that it's just business as usual.
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I was starting to have withdrawal symptoms waiting for the next installment! :D
That is going to be a lot of force on those outside walls, when are you going to put the reinforcement rods in place? Also, only those two little smoke holes? Or will another arch have more?
Putting in tie rods is the next step. Im just putting them in as I get to them, so they won't be in my way as I work through the oven body.
Regarding the smoke holes,
They're large enough for what I need, there won't be a tremendously large fire in there, no more than a couple pieces of wood at once and not much volume of smoke as you burn it hot an burn off the flammable gasses in the smoke.
Also the dry arches don't put more force on the walls than they are able to withstand, at least in the short term. The force lands fairly low on the brick walls, and the sheer strength of the mortar, though not high, is enough. Also the construction does ensure that the thrust is distributed fairly well into the outside wall
Early Monday morning, a bad storm (not on the forecast at all) rolled in and dumped several inches of rain. I hadn't bothered to cover the under-construction oven, as the weather was forecasted clear all weak. The rain washed the sand behind the arch support, allowing the arches to push them side and collapse. The suddenness of all of it allowed the arches to slide into outer wall with enough force to knock it over. SO progress has been delayed as I repair the outer wall of the structure.
From now on, I'll be sure to cover it even if no rain is in the forecast. IT is march in Indiana, after all.
The arches are particularly vulnerable when under construction. There is not very much holding them up at this point, and add to that that arches of this type are somewhat unstable without any load upon them.
Sorry to hear about your misfortune.
I was telling my future daughter in law about your project and she was very interested. Have you had time to get back on the project yet?
Hey, sorry for not replying sooner. Combination of busyness and travel, havent been on the forums a whole lot lately
The oven is not quite done yet, but hopefully I'll find the time to get to it soon. It's rained so much here lately that it's been hard to get too much done
Do I smell bread? My daughter in law to be asked about your project the other day.
Quote from: D L Bahler on March 24, 2017, 03:08:22 PMEarly Monday morning, a bad storm (not on the forecast at all) rolled in and dumped several inches of rain. I hadn't bothered to cover the under-construction oven, as the weather was forecasted clear all weak. The rain washed the sand behind the arch support, allowing the arches to push them side and collapse. The suddenness of all of it allowed the arches to slide into outer wall with enough force to knock it over. SO progress has been delayed as I repair the outer wall of the structure.
From now on, I'll be sure to cover it even if no rain is in the forecast. IT is march in Indiana, after all.
The arches are particularly vulnerable when under construction. There is not very much holding them up at this point, and add to that that arches of this type are somewhat unstable without any load upon them.
D L Bahler
This build was captivating, and the catastrophic ending as a result of the rain storm was very disappointing indeed. I have often wondered if a second undertaking ever happened?
@D L Bahler