May 2008

May 7, Upward push begins!! Block work is not very fun, that's for sure. I started by carefully measuring out and marking the base of the oven on the foundation, taking in consideration the spacings between the blocks. This required dry-stacking them first to make sure everything was ok. 

My friend Craig is helping out with some brick work. 

Looks like... something. Note that the top row of blocks, and each vertical corner is filled with cement and double 5/8" re-bar for reinforcement. I cut the inside of top blocks in such way that the rebar is placed horizontally all the way through all the blocks and connecting at each of the corners. This is called a "block beam" and it gives overall strength to the base. 

Framing for the hearth is put in place. Essentially it's just wooden boards that will support the cement board that I will place on top. 

Framing is done for the hearth, which will be the bottom foundation of the actual oven. The bottom is reinforced by sturdy cement backerboard, and the sides by 1" wooden planks, so the hearth slab is not actually attached to the base - it will be literally hanging on rebar, and supported from the bottom by the little block wall inside. This is done to insulate the oven, so it does not lose heat via direct contact with the base. I am ready for another pour of cement.

Note: This is considered the best practice but for smaller, back-yard ovens this may be an overkill. My oven's heat retention is incredible, it maintains cooking temperature for 48 hours, but it is a definite overkill for a backyard oven. 

2" of vermiculite/cement mix is poured first, as an insulating layer. This will harden to a tough but very light consistency, and will be a great insulator to keep all that heat in from dissipating into the surrounding masonry. 

Then the rebar, which is essentially resting on top of the block walls - this will make the entire hearth "hang" on the rebar without touching the surrounding masonry. Yep, this is the way it's done. 
Notice that the rebar is resting on another piece of rebar in the front and the back of the oven - this is done so all of the re-bar is resting on something, rather than just the rebar on the sides. 

The little insert for the ash slot is also visible here. 

Close up of the vermiculite mix. The mixture is 7:1, and is refreshingly easy to work with.

4" of concrete goes on top of the vermiculite. At this point I was really missing my concrete mixer. 

Looking like I am done here. The top doesn't have to be cosmetically perfect, but it has to be perfectly level. The wooden frame and shims will be removed once the concrete cures.
The weird wooden contraption sticking out of the concrete at the front of the oven is the beginning of the drop slot for the ashes from the oven. It will also be removed. 

.. and just let it cure for a few days, while keeping it moist. Being level at this point is the most important step.