Went to a cob oven workshop today

And built a cob oven.  Technically, it wasn't cob.  We made a 1 : 2 sand : clay mixture to form the inner shell.  The outer shell was very wet clay mixed with straw.

Tomorrow we're doing the earth-plaster layer.

It's definitely a lot of work! 

Well, I went to a rocket mass heater workshop today. 

Considering that I've been to a cob oven workshop I want to express that ... in my obnoxious opinion .... I win! 

Pbpbpbpbpbtttt!!!

It's going into a greenhouse.  Last night we ran the first fire in it.  Today we'll be finishing it up.  Pictures and video coming soon!

Heh, you are probably right.  This was my first hands-on experience with cob, and it makes a world of difference compared to reading about it or seeing videos.

I gotta get out of the 'burbs

Jeremiah, if it helps any, this workshop was in urban Atlanta .

I agree Tamo, you definitely can't learn how to make cob from a book! Good for you for going!

The first time I saw, sat on, touched and made cob at Cob Cottage Company in Oregon, I was not just impressed, but enchanted and amazed. I thought sitting on a cob bench would be like sitting on cement, but it's sooooo much nicer. (Even when it's not heated by a rocket stove.)

(Ignore Paul's raspberry - he's just really thrilled with rocket stove technology... )

I can't put up a greenhouse, which is the main thing I could use a cob or rocket heater for in my area. I'm looking at reselling my house in the semi-near future, and alt-anything doesn't really sell well in this neighborhood. I might try a rocket mass cob pizza oven tho.

As far as rocket mass tech, the closest I've come so far is a chimney type charcoal starter. Those things are awesome. Its all in the updraft.

Heh, I know. I'm actually enchanted by rocket stoves too.  The teacher and I were talking about them as an aside.

GRRRR!  I want to post comment's on Paul's new Cob Oven YouTube video, and I keep getting error messages!
http://www.youtube.com/watch?v=TvrUrnEIQoo

So I'm posting them here:

1) If you are interested in the double chamber cob oven, and want to see how it was built, check out Ernie's Picasa albums.  It shows the stages from plinth, sand mold, dome, insulation, and cob plaster, and we'll put up some more pictures of the decorative plasters soon.  http://picasaweb.google.com/eawisner

2) Definitely check out Kiko Denzer's book, build your own Earthen Oven, if you want more expertise and design details.

3) Earthen Ovens are a lot of fun, but nobody ever said they were efficient (even insulated ones).  The best efficiency is in running one oven day after day, so its warmth from the previous day is always used again.  In many areas a village bakery is the best answer to preventing a village wood shortage. 

We compromise by inviting friendly neighbors to bake with us, or join the pizza party, or both. 

Erica Wisner
http://www.ErnieAndErica.info

tamo42 wrote:
And built a cob oven.  Technically, it wasn't cob.  We made a 1 : 2 sand : clay mixture to form the inner shell.  The outer shell was very wet clay mixed with straw.

Tomorrow we're doing the earth-plaster layer.

It's definitely a lot of work! 

I am confused, how is that not cob?

Aren't I supposed to make a dome of sand, add wet paper over that.  Cover that all with a 1:1 clay:sand ration, followed by cob which in my case is 3 sand, 1 clay, and "X" straw over the initial layer.

Did I miss something? 

True cob would have straw mixed in throughout to act as a stabilizer.

tamo42 wrote:
True cob would have straw mixed in throughout to act as a stabilizer.

Hmm.  Now the question is should I add some straw to that layer or not.  I am finding I like my straw to be chopped up very fine as opposed to long and stringy (which was great at the base and building upwards). 

Also, that dang video Paul has up there has me thinking. 

/shakes fist happily

Darn you Paul!!

Straw in the inner layer will burn out.  The oven we dissected recently at Cob Cottage Co had burned-out straw for about 2 inches, in baked-red clay, then a transition zone, then intact, un-fired straw cob.

Many cob oven builders omit straw in the first layer, preferring to use very dense sandy 'plaster' that will be stable enough without relying on the straw's tensile strength.  Smooth plasters also drop less grit into the food - grit dropping on bread can be picked off, but that's harder to catch with pizza or puddings.  Some builders add a smoothing layer inside after removing the mold - can be a very thin finish plaster, or a spray of waterglass, or even just a wipe-down with a damp sponge.  It's always better to create a smooth mold and stout plaster from the start, than to try to patch it together again afterwards.
I suppose the straw does help support it during drying, before the first firing.

Straw is insulative, so some builders also favor omitting straw (or using brick) in the interior layer for this reason.  Dense thermal mass holds more heat for baking longer; then of course include thick insulation in outer layers to trap and reflect any heat that is trying to escape.

Any of these methods will work.  If you have local abundance of straw, or sand, or half a bag of perlite, or a lot of spare bricks lying around, use them to best effect. 

For pure efficiency of baking, the choice of more straw or more sand is MUCH less important than the number of bakers and dishes sharing one oven/bake cycle.  Choose a workable size to handle your normal baking needs in sequence, such as pizza, bread, biscuits, cakes and cookies, potatoes and casserole, drying things, and culturing yogurt or yeast, to make the most of each fuel load.  (I rarely get more than 3 dishes organized for one baking party, but I'm always glad to do more than one.)

Wow, thanks Ernie!  More food for thought.  Did Cob Cottage keep the dissected cob oven?  I would like to swing by and see it sometime, I am just across town, literally.

Hi again - sorry to deceive you, this is actually Erica, Ernie's computer just automatically logged me in as him.

Re: does Cob Cottage still have the dissected oven?
We built a new oven on the plinth where the old one was.  I think the dismembered old oven may have ended up in the garden.  I have a photo of one of the pieces we pulled off where it was cracked, or Ernie (the real ernie) can describe the layers in detail.

But it's worth dropping by for a look.  Especially if you live that close - do we know you by chance?
CCC has a Pyromania course happening in the middle of October, and if it fills up we'll be there to help teach.  Or just give a call and set up a private visit.  Their phone number is on the website at www.cobcottage.com

Yours,
Erica ("Mrs. Ernie") Wisner
http://www.ErnieAndErica.info

Ernie wrote:
Especially if you live that close - do we know you by chance?

Might remember me... I was there for the Mountain Homestead open house and brought vegan potato salad, my wife is disabled and staid at Cathedral while the rest of us walked over across the river & got the very grand tour of Cob Cottage.  I was asking about blue columbine seeds in the vegetable garden and was asking to trade my white ones with Ish if I remember right. 


Oh yeah, and Ianto just came back from New Zealand remarking about having to go back and see the Parliament building.