The Fresh Loaf

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Final layer of cob oven

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JennrB's picture
JennrB

Final layer of cob oven

last year my husband and i build a cob oven using clay from a pipeline that was being dug on our property.  we did 3 layers, a base layer, insulating layer then a final layer.  this year the final layer is cracking really bad and i have mud dobbers boring holes in it;and it doesnt look very nice. i was thinking of using a stucco or a fine concrete mix to protect it more.  any thoughts on this.   i will post pictures later when i get to my home computer.

 

 

tchism's picture
tchism

You want something that will breath and not trap moisture in the oven. I just finished applying a layer of lime plaster to my oven. It will still crack some as the oven expands and contracts which is normal for these ovens but so far they are fine cracks on mine. Also, you can apply line water to the cracks and they will seal themselves.

I made my lime plaster by purchasing a 50 lb bag of lime at Home Depot. Split it between two 5 gallon buckets and mixed with water until well mixed. It needs to have a layer of water on it as it settles to keep it from curing. Thats the water you can apply later to heal cracks. Allow the lime to hydrate for at leas six weeks to make a nice putty. then mix with sand (I used concrete sand) and apply a layer no thicker than 1 inch. Also, if you can get it, add cut up horse hair to the plaster for strength.

108 breads's picture
108 breads

OMG I am having oven envy just looking at your photo. How many loaves do you bake at a time? Can you bake just one bread? You can never move because that oven is so exquisite. 

tchism's picture
tchism

Thank you 108 breads! We have been enjoying the oven.

I have baked 4 at a time and could probably go as high as six if they were 1-1.5 lb loaves. the oven holds heat well enough that I could probably do two batches. I usually try to time the baking so that I can bake something for dinner after the loaves are done. we have baked turkey, chickens, pork roast and tri-tip so far and of course  pizza. With pizza, we usually make them first. Also cookies!

JennrB's picture
JennrB

That is a beautiful oven. So you mixed lime in 2 five gallon buckets with water. How much water? Then you let the lime sit in the buckets for 6 weeks before adding sand and applying to oven?

tchism's picture
tchism

Thank you Jennr B!

Yes, I split the bag of lime between the two buckets adding water and lime a little at a time while mixing. Use a paint mixer and drill motor. in the end you add water until you're about two inches or so from the top. Then put the lid on and let it set for at least six weeks. the longer you go the better the plaster gets. I actually went six months before I used it to be able to apply it without the fear of freezing. It also shouldn't be applied if its much over 80F. You want it to cure not dry.

I added sand until it was like stucco and would stick to the trowel. Applied from the base up. I went just shy of 1 inch thick and probably should have done it in two coats. I got some small cracking from it drying out too quick or from being a bit too thick.

One more thing, the the plaster has a white / gray cast to it when apply it. It will cure to a white plaster color unless you add something to color it. I chose to go old school and add Ferrous Sulfate to some lime water and apply it to the surface of the still curing surface. I was going for a Spanish Mission color look. Ferrous Sulfate is easiest found at ranch supplies in a product called blood stop. I guess it is applied as to animals with cuts or when they are to horned to stop the bleeding.

JennrB's picture
JennrB

Ok. Thanks for the help. My oven is in desperate need of some TLC. and wasp spray. The mud dobbers love the clay. The timing is just about perfect, I will be having my second child in 6 weeks so by the end of my maternity leave the husband and I can finish the oven with hopfully cool october temps. I will post some picturean when finished. I gotta fix my brick arch( it fell this winter) and my chimney pipe. 

tchism's picture
tchism

Yep them mud dobbers can be a real pain! Best of luck with BOTH of you projects and except my early congratulations! Pm me if you have any questions on the lime plaster.