Basalt alternative for loose thermal mass aggregate

[MarcD]

My friend and I are both building steel lined ovens. One with cast cladding and one with a loose aggregate contained by an outer stainless skin. I thought I had source for basalt but the minimum purchase amount is more than I need or have room to store at home.

I'm considering decomposed granite or crushed red brick with a fine gap filler material like polymetric sand. Is there anything with this material that I am overlooking?

[david s]

Adding a loose mix overcomes any problems of the layer cracking, but air spaces bettered loose aggregate will act as an insulator. In a wet concrete mix the spaces are filled with sand and any spaces between the sand are filled with cement and water. This creates a denser mix than aggregate alone with no spaces which makes the mix more conductive. You may have trouble compacting a loose mix. I presume you’ll have a hole near the top of the outer skin to load in the material. You could try vibrating the outer surface as you fill the stuff in to get decent compaction.

[MarcD]

You could try vibrating the outer surface as you fill the stuff in to get decent compaction.

This is pretty close to the plan. We tested out a theragun to vibrate the aggregate and sand into a very tightly compacted stainless brick form. Worked as expected and held heat as well as the regular clay brick sitting next to it.

I presume you’ll have a hole near the top of the outer skin to load in the material.

Instead of the typical top down style of outer skin I cut the steel in increasingly smaller diameter rings that will work their way up from the bottom. Hopefully this will allow me to tightly pack down the material one section at a time. The thought behind the polymetric sand is it's fine enough to take up enough space between the pieces of aggregate to allow for even heat retention. Last will be a 2 inch thick blanket and I'll work out a layer over the blanket after a few test fires.

Long term heat retention is not the goal for this oven. This thing is intended to cook quickly even if it means feeding a hungry fire. Besides, I can do masonry work anytime I want as this build will be easily taken apart. Most of the fun has been in the planning process anyway.