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Author Topic: Building An Oven  (Read 2612 times)

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Offline ljohnsaw

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Re: Building An Oven
« Reply #20 on: March 04, 2017, 11:25:27 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.
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Offline D L Bahler

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Re: Building An Oven
« Reply #21 on: March 04, 2017, 11:36:40 am »
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!)

Offline Czech_Made

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Re: Building An Oven
« Reply #22 on: March 04, 2017, 05:08:38 pm »
Any insulation to go under the oven?  So when you heat it up, it does not dissipated down?

Offline D L Bahler

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Re: Building An Oven
« Reply #23 on: March 04, 2017, 06:34:55 pm »
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.

Offline D L Bahler

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Re: Building An Oven
« Reply #24 on: March 04, 2017, 07:02:43 pm »
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.

 

 

Let the fun begin...

 

 

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.

 

  

  

  

  

 

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.

Offline D L Bahler

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Re: Building An Oven
« Reply #25 on: March 06, 2017, 08:12:19 pm »
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.

 

  

  

  

  

  

  

  

 

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

Offline D L Bahler

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Re: Building An Oven
« Reply #26 on: March 06, 2017, 08:18:22 pm »
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

Offline D L Bahler

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Re: Building An Oven
« Reply #27 on: March 07, 2017, 10:35:22 pm »
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)

 

 

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.

 

 

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.

 

 

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.

 

  

 


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

 

  

  

  

  

 

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.

 

  

  

  

 

Offline thecfarm

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Re: Building An Oven
« Reply #28 on: March 08, 2017, 06:11:12 am »
Like the buiding progress.
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Online Weekend_Sawyer

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Re: Building An Oven
« Reply #29 on: March 08, 2017, 08:06:35 am »
Very nice, I am watching with interest!
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Offline JRWoodchuck

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Re: Building An Oven
« Reply #30 on: March 08, 2017, 05:20:05 pm »
What is the benefit of dry stacking the interior wall?

Offline D L Bahler

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Re: Building An Oven
« Reply #31 on: March 08, 2017, 09:47:38 pm »
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.


Offline JRWoodchuck

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Re: Building An Oven
« Reply #32 on: March 09, 2017, 01:54:33 pm »
That makes sense. Do you ever see any issues with the sand pushing the bricks inward?

Offline D L Bahler

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Re: Building An Oven
« Reply #33 on: March 09, 2017, 10:19:49 pm »
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.

Offline D L Bahler

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Re: Building An Oven
« Reply #34 on: March 09, 2017, 10:36:22 pm »
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.

 

  

  

  

  

  

  

  

 

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)


Offline JRWoodchuck

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Re: Building An Oven
« Reply #35 on: March 10, 2017, 01:54:44 pm »
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....

Offline ljohnsaw

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Re: Building An Oven
« Reply #36 on: March 10, 2017, 03:36:59 pm »
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!
John

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Offline D L Bahler

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Re: Building An Oven
« Reply #37 on: March 10, 2017, 07:03:06 pm »
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.


Offline Bruno of NH

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Re: Building An Oven
« Reply #38 on: March 11, 2017, 01:52:41 pm »
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  :(
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Offline D L Bahler

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Re: Building An Oven
« Reply #39 on: March 11, 2017, 04:21:58 pm »
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.

 

  

  

  

  

  

  

  

 

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.