Clay Cob Oven Progress – Part 2

On Sunday, we put the final layer of cob on the oven. 

This layer we found was necessary as the oven did not keep its heat for more than an hour after an hour of fire.  It was 5 parts builders sand, 1/2 part clay, 2 parts sugar cane mulch (straw is fine).  All stomped in by foot by yours truly and young Benjamin.   We added a little water to make a firm mud.  Then Kim and I applied the cob about 4 cm thick over the dome, the top being about 5cm, and about 1 cm over the archway. 

I also fixed up the door seal.  It performed poorly during the first cookout, so I made it about 2 cm all around and placed the door against it when it was wet so that I could see if the clay left an imprint on the door.  That way I knew that it was touching all around the door.

This is the other angle.  Kim thinks it looks like a Hippo’s bum, but I just think it looks wonderful (the oven, not a hippo’s bum that is).  I checked it when I got home on Monday night, and it had a few hairline cracks, so I smoothed it all over with wet hands and pushed the cracks together.  The cracks form mostly because of air gaps between the lumps of cob when we applied it.

Here is the finish (click to enlarge).  As you can see, it is very sandy, but because I still used clay and straw, it has gone rock hard today.  I will give the oven a light firing on Wednesday night to speed up the drying, as Kim wants to apply the mosaics this weekend.  To do that, I will add a light coat of render made up of sand and cement with a oxide mixed through it.  It will only be about 1 cm in thickness, but should hold the mosaic tiles firmly in place.  At the same time, I will render the besser bricks, and fix up the mantle which I have the materials for.

I am anxious to see the finished product and hope it performs to my expectations.  It should lock in the heat, with all that extra thickness.   Another update next weekend.  Looking forward to inner clay oven artist in Kim bursting out and putting on the finishing touches.