After spending the last month extracting clay from my dirt and last week mixing and mashing a clay, wood ash, sand, and grass string cob I finally got it some molds yesterday. Not sure if I can post photos but this is what I have so far:
I sat it about 3 feet from my current wood stove to speed up drying.
This is a 4 inch core.
And the heat riser.
I slapped the molds together out of some scrap plywood I had laying around and used coffee cans to form the round openings. I filled bags with sand and stuck them in the coffee cans so they wouldn't get crushed by the mud. I figure if I can't just pull the cans out of the mud once it dries then I can punch the tops and bottoms out and pull out the sand bags one by one. I also used a solid block of wood for the port opening so that will have to be drilled out before I can burn the inside mold out. I used 2 inches of mud on all sides including the top. Not sure if that will hold up as most of these I have seen used bricks or a piece of refractory over the top of the box. I'm also not sure what ratio my clay/ ash/ sand mix is as I kinda just went by feel. If I had to guess I would say 10:6:3 clay/ash/sand with very little grass string in the mix to give it some fiber. I think my clay was a bit wet as my mix seems a bit runny. It can be rolled into a ball but it sticks to my hand so much it comes off my hand teardrop shaped and lands with a bit of a splat. Hopefully setting it this close to an active wood stove while get it to dry out.