Deciding on a Base

[Allen]

Hi, some friends and I want to tackle making a clay-type oven.
A friend and I made an elevated cooking platform out of locust logs for our dutch oven cooking to minimize always having to bend over to check on the food. Here's a photo taken not long after we had built it.



Could I do something like this for a clay oven?
There are some beautiful oven designs on this site but I'd rather not use concrete footers and cement block/bricks for the base if I don't have to.
I tried searching for info but didn't really come across anything for this question.

This thread has an oven similiar to what I'd like to try:
http://www.fornobravo.com/forum/f3/h...exas-3397.html

I thought about these types of bases:
A triangular log base.
A base that sits on 4 legs.
A base that is built into the side of a steep hillside with a log base.
A plain old 4-sided log base all made from locust logs.

Was thinking of a 32" to 36" interior dimensions for the oven.
thanks,
Allen

[Jed]

Re: Deciding on a Base

Hey Allen,

Any one of the base options you list could be an acceptable solution. The base needs to support the weight of the oven, and although the oven is heavy, any one of these options you list could be engineered to handle the load.

Most of us will choose the cement base (or cement block filled with concrete) because it won't rot or disintegrate over time; the base of the oven will remain stable and in one piece for a long time. Cement creates a solid base, that is structurally sound, that will support the weight of the oven, for a relatively low cost, over a very long period of time.

You can use the wood base, but this will likely be the part that fails on your oven first. It may take decades for the wood to rot, but that will be the reason you will need to spend time and money to either repair or dismantle your oven. If you use cement products, it will likely be something else that fails first before the base gives way....

My two cents....

JED

[dmun]

Re: Deciding on a Base

Many people, when they think "oven" think about that flimsy sheet metal thing in the kitchen. Masonry ovens aren't like that. They are really heavy, and rigid. They don't deal with shifting or vibration very well. They can crack, and collapse if they move around. That's why the masonry bases: they are stable and rigid, and they are far cheaper than trying to approximate the same rigidity with, say, welded structural steel.

The oven you linked to had a recycled concrete base: I didn't see a log in it except to burn.

Wood is constantly in motion. Every time the humidity changes its size changes: more against the grain than with it. It warps. Bugs like to eat it. I really can't recommend a structural log base for a masonry oven.

That said, it might be a cool facing material: bolt on logs to your structural base for a log cabin look with a rough split shake roof, and a big fieldstone chimney at one end? I think that would be great.

Good luck with your project.

[Allen]

Re: Deciding on a Base

Thanks for the replies.
We want to build this oven (hate to say it) on the cheap.
One of my friends was trying to talk me into cement blocks so maybe that will be the way to go.
Some of the ovens I've seen have two or three runs of cement blocks as a base.
Not sure how to pour a slab on something like that but I'll figure it out.

This link has an interesting oven: http://bensart1.homestead.com/breadovens.html

I may have access to mountain stone so that will give a more rustic look than cement blocks.
Allen

[Ken524]

Re: Deciding on a Base

Pouring the slab on the block base is pretty easy. Most any of our build threads have pictures of the process (you can click my "Old Kentucky Dome Thread" link below).

Also, download the "official" Forno Bravo plans for plenty of detail and pictures:
Brick Oven Plans | Build an Italian Brick Oven

[carloswlkr]

Re: Deciding on a Base

I agree with dmun, Ken and others about wanting to make sure your base is as solid as possible. Best to avoid wood, that can shift and will rot faster than you'd like. I would not want to experiment with different bases if you are building a fire-brick oven, and investing a fair chunk of change in the materials.

That being said, I suspect if you are making a clay or mud oven, you can probably find alternatives to the tested and true method of a cinder block and poured concrete base. If you're going with 'what's on hand', you might try some third-world construction techniques for your base. Looks like you've got plenty of rocks and/or boulders near that dutch oven cooking stand. Have you thought about piecing together a base out of carefully placed rocks, 'mortared' together with mud and straw? (see examples in my post on Honduras bread ovens.)

Here in Latin America, highways have retaining walls made out of wire cages filled with river rock. Box shells are made out of heavy chicken wire, approximately one meter square, then carefully filled with river rocks or other stone. The cubes are stacked one on another, and make retaining walls that last for years, and hold back incredible amounts of dirt.

You might experiment with one of these techniques. Whatever you do, make sure that it is on as solid a footing as humanly possible, and that the base is level all the way up. You don't want the floor to be on a tilt, or the base to shift because it wasn't build level to the ground. I would also make a solid base, not one with the traditional storage area below. This will give additional strength to support whatever oven you put on top.

Again, cinder block and poured concrete will produce something that will not let you down, and I wouldn't stray too far if you're building a brick oven. But I say, give it a shot!

[dmun]

Re: Deciding on a Base

Here in Latin America, highways have retaining walls made out of wire cages filled with river rock. Box shells are made out of heavy chicken wire, approximately one meter square, then carefully filled with river rocks or other stone.

This is a really good idea. These things are called gabion baskets and are used for highway construction. They can be made in custom sizes, but probably not on the cheap. Here's a link:

Welded Wire Mesh, Gabion baskets, PVC coated gabions, Mesh Fencing, welded mesh rolls, weld mesh panels, stainless steel, galvanised

[gjbingham]

Re: Deciding on a Base

Dmun's caged rocks sounds very similar to how the landscaping firms around here sell landscaping stone by the ton - all caged up and on a palate. From the prices I saw today, a ton of the cheap stuff would still cost more than a concrete block base.

[carloswlkr]

Re: Deciding on a Base

True, if you are going to buy the stone, it may well cost more than a base of block and poured cement. But if you've got the time, and rock is plentiful on your property, it might still be one option for doing it yourself and not investing in materials other than the heavy gauge chicken wire.

[Allen]

Re: Deciding on a Base

Thanks everyone for the replies. I wasn't around for a bit due to work.
I've got a backhoe rented for this coming weekend to do some work around our place and am planning to dig a foundation for the base.
I am also able to get as much field/mountain stone as I need for the project. For free.

My dad and I built my forge out of similiar field stone, check this out:




I feel confident that good sized rocks similiar to what you see in my forge will easilly support a cob-style oven.
Am planning to dig down about 36".

I was using the search feature but couldn't find an answer to some questions.
The foundation will be square.
For a 32" to 36" cob-style oven, how wide should the base be?
I've also got a bunch of 2a driveway stone.
Should I place the field stone on a bed of the driveway stones first?
Or just let them sit in the dirt at that depth?
Was planning on filling the center with dirt and loose rocks.

thanks,
Allen

[dmun]

Re: Deciding on a Base

Just a quick question, why cob? As a smith, you must know how important proper refractory materials are to reflect and concentrate heat from a fire.

For you base, it's always best to build on a base of well drained crushed rock, unless you are digging down below the frost line and pouring footings on bare rock.

My 1920's concrete block outbuilding was built on shallow field rock footings, mortared together, but it did crack in a couple of places. I still think you're better off with proper footings of one kind or another.

[Allen]

Re: Deciding on a Base

Hi, thanks for responding.

Just a quick question, why cob? As a smith, you must know how important proper refractory materials are to reflect and concentrate heat from a fire.

For a gas forge, refractory like kaowool and ITC-100 play an important part.
For a coal or charcoal fire, refractory plays no part.

I like the look of cob and how its made. Its more of a rustic construction than brick.
Are you saying that cob is that much less efficient than a brick oven that it isn't worth pursuing?
If cob is that bad then we'll have to look at brick construction.

How shallow are the footings on that outbuilding?
Here in Pa., 36" down should be fine for what we want to do. Unless I'm not understanding what you mean.
Allen

[dmun]

Re: Deciding on a Base

If you are going down the 36 inches, then you're under the frost line, and you can build direct on bare ground, no problem.

I'm not arguing against the cobb, I'm just wondering why someone used to managing fires for high heat would make that choice. If you like the look, that's all you need to know.

[james]

Re: Deciding on a Base

One thing about getting the look you want. The oven itself can be brick, alla the Pompeii Oven, but you can finish the exterior of your oven any way you want. You can have the advantages of a real brick oven -- high heat cooking, better heat retention, longevity, etc., and still get the rustic, hand-hewn look on the outside.
James

[geisen]

Re: Deciding on a Base

Pompeii ovens have been around for .......well, as long as Pompeii. I walked through the steets of Pompeii and Herculenium many times and always enjoyed exploring the sidewalk store-front pizza stalls with WFO dome ovens just like we are all making. Yes, their bricks were probably not made with exactly the same materials and I highly doubt they had wet saws, but the basic engineering was the same. Some of them looked like you could just start a fire today, even after being buried by lava dust for generations. Way cool. My avatar is from the pompeii theater. seemed appropriate.