I poured the perlite layer over the entire hearth slab. I mentioned in a post on Fornobravo that I was not sure how to anchor the steel frame of the oven enclosure into the perlite layer. Here’s what I ended up doing:
I snapped a chalk line to give me about 5 inches of perlite insulation from the hearth brick to the inside surface of the future wall. Then, I used a wide putty knife and a hammer to cut out blocks of perlcrete. The blocks came out easily, and will come in handy when filling the enclosure with loose perlite.
Some photos of the process:
Having exposed bare concrete, I used a powder-actuated nailer to shoot 1-inch nails through the steel track and into the concrete slab. It was a lot of fun!