Here are the first, second, third, fourth, and fifth posts in this series (you can also go to the “bread oven” category, in the lefthand navigation menu).
With the oven chamber completed, it feels like we’re in the home stretch. Time to add mass to the oven, to retain heat. This thing is going to get crazy hot. Pizzas are cooked at 650-800°. The oven also needs to maintain high temperature for a long time. Bread is cooked around 500°, after the coals are raked out of the oven. Lots of mass and insulation ensure consistent results.
First, Jan built a removable plywood form, into which the concrete would be poured.


Then Ken and Jan wrapped the chamber with tin foil, to shield the bread from cosmic radiation. Actually, it’s to prevent the concrete mass from adhering to the chamber structure. This will allow expansion and contraction in the chamber, without breaking up the concrete layer.

Next they replaced the form, and inserted rebar around the chamber structure.


Please note the stretch of space on the side of the form where there is no 2×4 supporting the plywood. This will become important later.
Next, massive quantities of concrete were mixed and shoveled into the form. When this project started, Jan and Ken were carefully measuring water to add to the concrete mix. By this point, they were mixing their own concrete from scratch, and eyeballing the water from a hose. Skills have been acquired.

Concrete is heavy. Really, really heavy. So as the boys were shoveling, they began to notice that the sides of the plywood form were bowing out. Note to those who come after: reinforce the plywood along the entire length. Otherwise, you’ll need an emergency retrofit:

The good thing is that this will all be covered up by the outer brick-work. So no harm done. The form came off a couple of days later, and our commitment level ratchets up another notch.
Notice the inset wooden form at the top front. That is where the chimney will be.

At this point, Jan and I reflect on permanence and attachment. He told me we could never move now. This is a funny thing to say to me. I have never in my life lived in a house for longer than 4 years. We, as a couple, have moved 6 times into 7 houses in our 9 years together.
“You told me that this oven was built on a floating slab, so that it could be detached from the base and moved,” I say.
“Well yes,” he says, “moved across the yard or something.”
“Across the yard?” I am incredulous. “What the hell good is that? Why can’t we take it with us?”
“This thing weighs as much as a Hummer!”
“I see Hummers moving around all the time.” Too often, if you ask me.
“But they have wheels!” Now he’s incredulous.
“So, get some wheels for this thing. We’ll hitch it to the van.”
If we do end up hitching this thing, I promise I’ll share pictures.