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Step 1: Cob Oven

Grover Greenie


Joined: Feb 20, 2013
Posts: 1
I am so glad I found this forum. I live in Alabama, and recently purchased several acres of vacant land. After a few weekend excursions, we have determined we have around 5 springs bubbling up out of the ground and running to a large creek. The clay ground is in abundance here. So are the giant sandrocks, and what we call sage grass (that can be used as straw in building) I hope at least. our goal is to build a round cob house, completely off grid.

We decided to start small with a cob oven. So our base is build up with fieldstone. Today, We added our first cob layer. Then a lip with bottles enclosed in it. We learned alot but I am still concerned about the structure and drying time. We covered it with a tarp tonight, and will continue finishing the base layer of the oven next week with the firebricks, sandcastle, and cob covering.

I guess my question is does it look right?we didnt completely finish covering the bottles because we ran out of the cob we had mixed up and time had run out for us to make more before we had to head home. Any thoughts or opinons are welcome. Are we going about this the right way so far? I know cob is very forgiving, so if we blew it we can just try again next weekend i guess.



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Jim schalles


Joined: Mar 03, 2013
Posts: 23
    
    1
The idea behind the bottles is to provide air space/pockets of insulation to keep the heat over your oven floor from travelling down and absorbing into your foundation. It will take a longer time and more fire wood to bring this thing up to the temperature you want it. It is best to use a mix of clay slip and sawdust, or perlite or pummicestone and as many bottles as you can comfortably fit. Something with a lot of air pockets and good insulation. This might work, and I would say go ahead and finish the build. But if it is taking more wood and a longer time than you had imagined, I would return to this step. Good luck!!
Miles Flansburg
steward

Joined: Feb 03, 2011
Posts: 2120
Location: Zones 2-4 Wyoming and 4-5 Colorado
    
  52
Howdy Grover, welcome to permies.
That is the first time I have seen anybody put bottles in a cob oven.

Maybe a dumb question but won't the bottles blow up if they get to hot?
Tys Sniffen


Joined: Nov 05, 2012
Posts: 28
Location: Northern California
    
    1
this is from a while ago, but I thought I'd chime in anyway -

that base and cob with bottles looks fine. (you're probably baking in this thing by now!) As long as you plan a decent handful of inches between what's in the picture and your oven floor, you should be fine.

I didn't read too closely, but I assume you're taking the typical advice and using fire bricks as the oven floor? if so, the needed sand to level them plus their height alone will be plenty of mass between your heat and those bottles. seems like a fine way to take up some space.

another assumption I'm making is that your rock base is very secure... it looks fine in the photo, but one would want a base that some teenage boys could run up to, pounce on and spring off without a rock moving around. if that's what you've got, you're good to go.

cheers,
Tys
Rion Mather


Joined: May 31, 2012
Posts: 644
    
    1
Tys Sniffen wrote:this is from a while ago, but I thought I'd chime in anyway -

that base and cob with bottles looks fine. (you're probably baking in this thing by now!) As long as you plan a decent handful of inches between what's in the picture and your oven floor, you should be fine.

I didn't read too closely, but I assume you're taking the typical advice and using fire bricks as the oven floor? if so, the needed sand to level them plus their height alone will be plenty of mass between your heat and those bottles. seems like a fine way to take up some space.

another assumption I'm making is that your rock base is very secure... it looks fine in the photo, but one would want a base that some teenage boys could run up to, pounce on and spring off without a rock moving around. if that's what you've got, you're good to go.

cheers,
Tys


Why would you use firebricks instead of the regular bricks for the oven floor? I have read that the standard clay bricks should be used for ovens.


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Tys Sniffen


Joined: Nov 05, 2012
Posts: 28
Location: Northern California
    
    1
Well, in mine - that has been working great for 6 years of baking just about every week - I used fire bricks. I believe I got the idea that those are what you *should* use from Kiko Denzler's book (which you should totally read and watch his videos: http://www.motherearthnews.com/diy/build-your-own-wood-fired-earth-oven.aspx#axzz2U89J7y6U if you haven't already)

and I'm pretty cheap, so given that regular bricks are cheaper than fire bricks, I would have used those if I'd had the chance. So some argument was made that made up my mind. I doubt regular bricks will burst or ruin your set up, but if you're doing this, you might as well build it to last a while and spend the extra (what, $10?) on 'fancy' fire bricks rather than regular. and, given that they're fire bricks, if your oven falls apart (and it will, eventually) they will still be just fine and you can re-use them)

you can see stuff from my blog about our oven at:
http://journeyinthewoods.blogspot.com/2007/04/started-on-earthen-oven.html

and

http://journeyinthewoods.blogspot.com/2012/08/fruit-tank-smoke.html

and

http://journeyinthewoods.blogspot.com/2007/08/hot-hot-hot-since-its-been-really-hot.html

Tys
Rion Mather


Joined: May 31, 2012
Posts: 644
    
    1
Cool. I will check all those links out.

Maybe it was the type of firebrick? I remember reading somewhere (Sorry, but I have been on so many different sites lately that I forgot which one) that the firebricks would hold the heat instead of reflect it as well as the regular bricks.
Tys Sniffen


Joined: Nov 05, 2012
Posts: 28
Location: Northern California
    
    1
maybe that's true... but I might argue that what you want IS absorption, rather than simple reflection. the whole idea of the cob oven (in my opinion) is thermal mass, not reflective radiation. You have a 3 hour fire that heats the cob (and bricks) and that heat is stored in the mass for the next 3 hours - with no fire in there - so you can bake.

if your floor bricks didn't soak up heat, you'd have a cold floor and a hot ceiling, and have uneven baking. just my thought process... I have fire bricks as my floor, and my floor is hot when I'm baking.
Tys
Rion Mather


Joined: May 31, 2012
Posts: 644
    
    1
I love Mother Earth News!

Your cob oven looks fantastic! Great job. I am going to bookmark this thread.
Amanda Eur


Joined: Feb 27, 2013
Posts: 4
Hello

I plan on building a Cob Oven soon. I live in West Palm Beach, Florida and was wondering where do I get the clay? thank you.
allen lumley
pollinator

Joined: Mar 16, 2012
Posts: 2243
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
    
  37
Amanda Eur : The very first thing I would do Would be to start new Posts in the Forum >>Thread - - - Building >>Cob, and Regional>>SouthernUSA. A short catchy title is
best ! I would identify myself and my location and an approximate cob oven building date. Ask for people in your area to Identify themselves. You may have an Experienced
near neighbor, with clay !

The next thing I would do, is learn how to do a sedimentation test, when you find your clay you need to have an idea of how much sand you might need to make a good Cob !
While you can google this information, you need to start a small Cob Library for this job - -

Looking for free I would ask local Dept. of Public Works, D.P.W., Agricultural schools, county/State Highway Dept.s and local 'Sustainability Groups', and a local soil conservation
district, next I would try the yellow pages, look under Excavation Contractors, I would tell them it is an Art project and you are trying to recreate an ancient technique- and it
will be an outdoor piece, If you have a good hustle you can get a load delivered for a couple of cases of beer !

Before you take delivery, know how much clay you will need. This will come from the plans that you find to follow, don't let a contractor unload 5 cubic yards if your whole
Cob Oven needs a 1/2 cubic yard, 2/3rds of which will be sand! Remember from the pictures above that more than 2/3rds of the total mass can be insulation for the base +
chunks of old concrete for thermal mass! You dont want to end up stuck with most of a load of Clay that you will have to pay someone to load up for removal, and then pay
someone else to haul away ! Can you say silly xmass presents for 30 years ?

There are several books out there that will help you find good plans, - ' cobcottage.com ' - is a good place to find people who can help you ! For good gently used books you can
go to the #1site Amazon, or google my pick, Alibris books, with either site you can type in search terms Cob or Ianto Evans will get you into the 'right section' and then both
sites will show you a list of people who looked at these books also looked at - - - ! For general Cob Construction there is probably no better book than Ianto Evans' et al book
'' theHand-Sclpted House '' I would also look at " Instructables", a lot of good people there ! I would however be careful of taking advice or plans from You Tube, there is some
real jreck out there !

For the future good of the Craft ! Be safe, keep warm ! PYRO big AL ! - As always, your questions and comments are solicited and are Welcome ! A. L.












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