Cob Oven Update #5 - She's Hot!

Yesterday i could not stand it any more so i built a fire in Craven, have i mentioned her name is Craven?, with the intention of baking some pizzas. I must say I was a bit apprehensive about getting her all hot and bothered. For all i knew she could totally collapse in a heap of mud... or explode into a million pieces. I built a fire out of old pallet wood and kept it blazing for 2 hours which i figured would be good enough for cooking a couple of pizzas. The fire door worked great at promoting good air flow while allowing easy feeding and tending of the fire. I used the blow pipe a couple of times to rev up the flames.

As darkness fell it decided it was now or never. I assembled the pizzas and (attempted) to put them in the oven :-p It was at this point that I began to learn a few things about cob oven in general and this oven in particular.

This is What I Learned:

1. I need a proper peel- sometimes DIY is just not worth it. I found a restaurant supply on line from which i can get one for under $10.00. Ordering it next.
2. Use a flat surface on which to assemble the pizzas - a cookie sheet with a lip does not allow one to effectively slide the peel under the pizza without messing it up.
3. Do not put too many toppings on said pizza - they fall off with handling.
4. Calzones are easier to handle that pizzas - and taste just as good.
5. It takes a lot of foreplay to get Craven really hot - 2 hours of firing was not enough to heat her enough to even cook pizzas properly. I am guessing 3 hours minimum and 4 hours + to getter her hot enough to make buns in the oven, i mean, bake loaves of bread. This suggests that the abundant thermal mass in this oven will retain heat for a long time once it finally reaches maximum temperature.
6. I need to start stockpiling lots of firewood - i have enough for probably one good firing. I am going to keep my eye open for construction sites, few and far between in this depressed economy. and start cutting brush around here that we've been planning to do for a while now.

While we did have to finish the pizza and calzone for a few minutes in the oven, they tasted great. Smokey, with a nice bottom crust. I look forward to the next time we get to fire her up!

Cob Oven Update #4 - Tools of the Trade

The oven is essentially finished. After she dries out well i will put the final coat of plaster on her. She is about ready for her maiden voyage into baking though. i built a test fire in her last week and she breathes very well.

I have been making the tools i will need for the firing and cooking while i wait for her to dry out a little more.

These are the tools of the trade:

This the rough form of a peel. It will be used to place loaves of bread and pizzas in the oven and peel them out when they are finished baking.








This is called a scuffle. i made it from a paint roller extension pole, a nail, some copper wire and an old cotton sock. It will be wetted and used to swab out the remaining bits of ash in the oven before the loaves go in. The moisture left in the oven turns to steam and helps to create a nice chewy crust.







This tool is the rooker. It is used to scrape the coals and ashes out of the oven before the baking begins. I connected an ell bracket to a watering wand with a couple of screws to make this fine tool.









This precision tool is an oxygen delivery tube a.k.a. blow pipe. I will be used like a bellows to blow air into the fire to keep it burning evenly. I smashed the end of a 1/2" copper tube with a rubber mallet to flatten it out to provide a wide focused flow of air to the fire.







This is a fire door I fashioned out of a piece of aluminum flashing, a couple of ell brackets and a piece of copper wire. It serves as a temporary chimney improving the draft in the oven especially on windy days. Cool air flows into the oven along the floor and circulates up the the top of the oven and out the top of the door. When the wind blows the flow becomes turbulent and the wood does not burn efficiently. The fire door deflects the wind keeping the fire burning efficiently thus using less fuel to heat the oven.



This is the baking door. It is made out of cob with a piece of bamboo for a handle. Right now the damn thing weighs about 40 lbs. Hopefully when it dries out it will weigh a good bit less because it is very difficult to handle right now. It should keep the heat in well though.

We are very excited to fire her up and bake something soon. With the holidays fast approaching it may be next year before we try her out.

Cob Oven Update #3 - The Key to Cob is Community

Saturday before last the permaculture class came out to the Funny Farm to work on the cob oven. There were 14 of us all working together to make it happen. I gave a brief orientation about how a cob oven works, what the various layers are made of and where we stood in the process. We then divvied up the various task and got to work.

One group worked on the sand dome that would support the cob that forms the inside of the oven and is the layer that will absorb and retain the heat for cooking. 2 other groups started mixing and stomping the sand/clay mixture to make the cob. It was very exciting to experience how quickly we gelled into an efficient team to get the job done. Within and hour and a half we had completed the sand dome and applied the first layer of cob. Thanks to Brandy and Keri for bringing their group out the help.







Sunday i cut out the door opening and then took a break from cobbing to let my weary body recover. Cobbing is hard work :) And fun work too!

On Monday my friend Deanna came out to help me apply the next layer, the insulation layer. We built a large lip of structural cob around the door opening to support and contain the insulation. We mixed together clay slip (screened clay and water) and wheat straw and layer it over the whole surface of the oven in a 3-4" thick layer. This layer is not packed down so there will be air pockets that prevent the heat from being conducted out of the inner cob layer to the outside surface. After Deanna left i began to sculpt some of the features that will give the oven a Funny Farm flair. I added an eyebrow, an eye and the upper lip.

On Friday i covered the insulation layer with a layer of structural cob, clay/sand/straw. The straw acts like rebar giving the cob shear strength.

Yesterday i did some more sculpting using up the remaining cob i made on Friday. I added a lower lip and one cheek. I have determined that the oven is a female. Someone on Facebook asked me what her name is. She has not revealed that to us yet. All in its own time.

If the weather is good tomorrow i will finish up sculpting the rest of her features. After that we will let her dry until after the end of the year before we put the final plaster coat on her. This Sunday we will probably build a small fire in her to see how well she breathes and because i can't stand to wait any longer.

We are so excited about having fresh bread and other yumminess cooked in our own mud oven in the foreseeable future!

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Cob Oven Update #2 - The Base is Complete and Ready for the Oven.

Today i finished the base for the cob oven.

The Insulation Layer
We want to retain as much heat in the thermal mass of the oven as possible. I made an insulation layer below the fire bricks that will be the bottom of the oven to keep the heat from being conducted into the oven base. The principle here is the same as with double paned windows. Air is a poor conductor of heat. First i placed empty bottles and jars on their sides. The insides of the bottles and jars are filled with air. Then I filled the spaces between them with a mixture of sand, clay and a good bit of straw with a little portland cement mixed in for strength. Straw is hollow so it is a poor conductor of heat as well.

The Final Layer That Will Support The Fire Brick.

I finished off the base with a 1 1/2" layer of structural cob which is just clay and sand in a ratio of 1 part clay to 2 parts sand. I determined the ratio by making test bricks a few days ago. I made same sized bricks using different ratios of clay to cob. 1:1, 1:2, and 1:3. I dried them in the oven using low heat. The 1:1 ratio brick shrank a lot. The 1:3 brick turned out deformed and slightly crumbly. The 1:2 ratio brick is perfect! That is the ratio we will use when we make the cob tomorrow.

Cob Oven Update - base almost complete. Bourbon bottles almost empty.

Today i worked on the base for the cob oven. The base of the bench is finished. The oven base is at its final height but i ran out of materials to finish it. Good thing too, cause i am totally whipped!

Tomorrow i will get some more sand and fire bricks and complete the base. I also need to make some clay slip and start staging materials for the day of fun on Saturday.

Oh, yea, those bourbon bottles will be part of the insulation layer under the fire bricks. Looks like I probably need 1 more. Could be a long night of drinking ahead ;)