Worked on filling the voids in the floor, and strengthening the foundation under the primary air today.
Here is the finished floor with all the voids in the shelves filled with hard castable, as well as everything around the edges. The upper tiers of the first chamber are filled with insulating rather than hard castable. Just a little experiment to see how it holds up.
The bricks at the front of the firebox were loose, because we hadn’t brought the foundation that extra half brick out in the center. Fixed that with some more hard castable and a leftover piece of castable slab that was laying around. Also laid a PVC pipe underneath the slab and poured the castable around it, even if the heat of the kiln melts the PVC, a castable pipe will remain for water to drain into the sump from the front of the firebox.
I wadded up a pair of cloth gloves in the kiln end of the pipe, to keep the castable from plugging the pipe. I tied a string to the gloves so they can be removed later, hence the pink string in the picture. The sump will be enlarged and lined, and an automatic sump pump with floats will be installed, ensuring that the firebox will never flood during heavy rains.