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Kiko Denzer on Art

[Cob] A cleaner cob oven for the future

Joseph Kennedy livingearth62 at
Wed Apr 7 13:13:33 PDT 2010

Hi guys,


I rarely reply to these posts, but feel compelled this time.  I have built about 10 cob ovens now, and have to say, while they are sexy, cook in a fun way, and are great workshop projects, they are a very dirty (for the air) way of cooking, and (IMO) nothing will ever make them anything but overly-polluting.  I had a big turn-around in South Africa, where I saw how desperate people are for wood, and how it is important to create super-efficient wood burning ovens (not just stoves).  


I designed one based on a project in did in Argentina ten years ago.  I have plans and some photos if folks want to get in touch with me separately.  It's basically a 55 gallon barrel on its side, weld rails on the inside of the barrel to hold custom built sheet metal baking pans.  One end of the barrel is the door. Arched end walls hold the barrel ends, and a vault that doesnt touch the round side of the barrel (about 1-2" separation is good), contains the wood smoke.  A small firing chamber is underneath the barrel, the heat flows up and around the barrel and is vented out the top of the vault.  A layer of sand in the bottom of the barrel serves as a heat sink and to modulate the heat.  Much easier to manage the heat, and super more efficient, and you can cook much sooner.  And you don't get your eyebrows singed and a bunch of smoke in your face.  The only drawback is that you don't get quite as much of that smoky taste.  But I'm sure there's ways you can do that (maybe a few holes drilled in the barrel to allow a bit of smoke).  


Sorry to burst the cob oven bubble, but I feel increasingly wrong advocating the typical burn-a-big-fire-in-an-earth-igloo approach.  This is coming from one who loves to do so, so it pains me to say it.


If you must make a typical cob oven, I have had success with a high mass inner layer, covered by a thick perlite cob layer (thickest at the top of the dome).  This helps keep in the heat.  My biggest advice is to let the cob oven dry slowwwly.  I've also put in some rebar and welded wire mesh as I build to help control the inevitable cracking (especially at the top of the door).  Cracking is inevitable, though, I find.  Another cool thing is to make a place to put a pan at the smoke hole.  Kinda like a rocket stove.  Fry up some onions and stuff while you are heating up the oven!  Chimney's are great, but the heat escapes too fast.  A good plug for the smoke hole is best, I think.  I agree that waist height is the way to go, with counters on either side.   I prefer a modified Quebec-style with smoke hole.  I usually in this case cook in cast iron pans on loose bricks set in the oven.  The coals and ashes filter down between the loose bricks, and cooks from below, while the pans are closer to the roof of the oven to get that good radiant heat. (the loss of heat and mess of removing ashes and cooking on the floor of the oven where it is coldest seems foolish to me). 


See this version at  look for the photos, and check "cob pavilion" for some photos of the oven (as well as some other groovy cob features).  We had to do a chimney in this case for fire danger.


All the best,


Joe Kennedy
> From: otherfish at
> Date: Wed, 7 Apr 2010 10:58:02 -0700
> To: coblist at
> Subject: Re: [Cob] A cleaner cob oven for the future
> Ray,
> Have you considered the heat expansion difference between the steel 
> dome and the cob covering? Wondering if it will be enough to crack 
> the cob covering.
> john fordice
> On Apr 6, 2010, at 10:14 AM, Dulane wrote:
> >
> > Dear Cobbers,
> > I'm days away from test firing this inner chamber cob oven and 
> > wantd to
> > share the news. If it works as I know it will, you'll be creating 
> > these
> > incerts like this stainless steel igloo shape. The heat from the 
> > fire is
> > rapid and I see closing the stack after the fire is out to hols in 
> > the heat.
> > Otherwise you burn for hours with black smoke killing the 
> > atmosphere. SunRay
> > Kelly will tell you as well, we have junkyards here in LA that have 
> > it all
> > that can change the way we build.
> > 
> > be13-6f4aeee03a7
> > 7
> > Ray
> >
> > Dulane - Keep us posted. It would be interesting to figure out a 
> > comparison
> > test between a similar clay oven and your hybrid. But if it helps 
> > keep heat
> > and reduce smoke, great idea!
> >
> > The trouble I've had is that mine got damp and cracked since I 
> > didn't have a
> > serious roof over it. But if you were going to use it often, you'd 
> > want a
> > serious design. And one that wouldn't allow too much cob crumbles 
> > to fall on
> > your food (from my deteriorating oven ceiling). I only use small 
> > scrap wood
> > and branches that fall out of my trees to heat mine, then I throw 
> > in a few
> > pieces of alder or fruitwood near the end for flavor.
> >
> > Your oven seems like a well thought out design (chimney damper and 
> > all) for
> > a small community, but the old design (w/o metal) is still 
> > efficient for
> > folks who just want to bake pizza or fish outside several times a 
> > year. It
> > pays to build them at waist height too, so you aren't bending over 
> > all the
> > time. I am building a new oven this year...and it will have a small 
> > work
> > area by the oven door. I'm tired of my dogs trying to help me cook, 
> > because
> > I'm down at chair level.
> >
> > Would you have to find someone to weld a dome for you?
> >
> >
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> >
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