Cob Oven

[jagarvin]

Hi,
I have finished my first cob oven. I think I may have made an error with the inside of my dome. I used clay, straw, and sand mix. From what I have read now I should not have used that on the interior of the dome, but only clay ,sand mix. Is this going to be a problem?
Thanks

[Rocko Bonaparte]

Re: Cob Oven

The idea behind the straw is that it will insulate when used in significant amounts. In smaller amounts, the straw might actually help you out. The straw can provide some breathing room for everything to expand and contract. I didn't use straw here on mine so I can only speak generally about it.

[david s]

Re: Cob Oven

It won't matter, You might get the odd void right on the surface, but so what. Some of the straw that is close to the inner surface will just burn away. be sure you give it plenty of time to dry before attempting any fires. If it is fine weather try to let the sun and wind do most of the drying, but you will need to cover it if there is a threat of rain. A cover that allows air flow over the dome but shelters it from rain is good.

[zeker]

Re: Cob Oven

I too am confused about this.. in some spots it says.. use no straw on the first (oven) layer.. in others , it says to go ahead and use as ithe straw burns out and leaves small voids for expansion. watching the utube vids of folks building with cob, it seems they use the cob rite from the sand form.. color me confuzzled.

[madKW]

Re: Cob Oven

Hi all, I think its a case of get as much advise as you can then do what you think is best. I to am in the same boat ,no straw or straw ? I think I will use SOME straw but not alot
Cheers

[david s]

Re: Cob Oven

For the insulation layer use as much straw as you can with just enough slip (clay and water) to bind it. The insulation layer does not get hot enough to burn the straw.

[Tscarborough]

Re: Cob Oven

If you are going over a sand form, make your first layer with no straw, about 1/2" to 1" for a solid face, then continue adding straw as you build it up. The last 3-4 inches should be straw covered with a slurry of sand/clay mix for insulation.

[madKW]

Re: Cob Oven

Thanks for that.So 1/2"-1" for the face with no straw, then 3" with a modist amount of straw ,then 3"- 4" of lots of straw for insulation and finally a thin layer with little straw to render the dome . Does that sound about wright ? Thanks for the help

[david s]

Re: Cob Oven

Thanks for that.So 1/2"-1" for the face with no straw, then 3" with a modist amount of straw ,then 3"- 4" of lots of straw for insulation and finally a thin layer with little straw to render the dome . Does that sound about wright ? Thanks for the help

Yes that's it. After you've fired the oven lots and the cracks in the outer shell have shown up, you can fill then with more mud and then render the whole thing with a sand,lime, cement coating. I use a 4:1:1:1 mix around 15 mm thick.

[madKW]

Re: Cob Oven

Grt thanks for that. I will finish putting the decomposed granite down this weekend so that will be the area done ,next will be the pizza oven stand then the oven its self.Soon I hope

[madKW]

Re: Cob Oven

Hi all got the decomposed down last weekend ,it came out really well good and hard and flat thanks to a mates plate compactor .It only got away on me once and smashed a pot plant and a porcelain elephant.It must have looked like a episode of MR Bean.Anyway it all came out great. Tomorrow I go and buy a compound miter saw and all the timber needed to build the stand over the weekend .If its not to hot, 38 in my back yard at 5pm today so working outside in that temp is not for me
cheers
Marty