Adding Hearth Insulation Layer

Above the layer of Rocks we added the bottom insulation layer which insulates the hearth (the oven floor) from the base of the oven.
We chose to make the insulation out of empty glass bottles set in a combination of grass clippings (which we collected from a large pile which remained from mowing a soccer field) with clay slip (clay mixed with water to make a clay 'soup').
The layer of insulation is 5 inches thick.
In the pictures can be seen: Grass clipping mixed with clay slip, and the finished insulation layer.