Refractory Mortar under hearth

[adam.darrow1@gmail.com]

Hi All. Newbie here building a barrel vault oven. I'm building in Laos and some of the building materials are difficult if not impossible to find here. I'll be using red clay bricks in the build, along with homebrew refractory mortar made from 3:1:1:1 sand, Portland cement, lime, and I was only able to find fresh, wet red clay rather than clay powder. First question is, will the wet clay still be effective when I'm just mixing it in with the rest of the materials? And my second question is, can I use just that homebrew mortar under the hearth as insulation, as well as an additional layer over the brick barrel before rendering with something more aesthetically pleasing like tile? Will the homebrew mortar be effective enough for insulation by itself, or am I screwed if I can't find proper insulation material? Can I just cover the brick barrel in a thick layer of the wet fire clay? Sorry for the slew of questions! Thanks for any advice you can offer!

[JRPizza]

Adam, the homebrew mortar is thermal mass, and some builders even use it for the heat retaining oven walls. It is not insulation. You are going to need to find something to use under the floor and around your barrel or the oven will be very difficult to heat and will cool very fast.

[david s]

Wet clay will not mix with the other materials. It will not disperse into the mix wanting only to stick to itself. It needs to be powdered. To convert its state from plastic to powdered, you can break it into fist sized pieces, dry it thoroughly in the sun, then pulverise it into powder, but this takes a fair amount of effort. For insulating material try vermiculite or perlite. If they at unobtainable and you are near a beach you may be able to find pumice stone. Sawdust is another option if you are close to a sawmill or chopped straw. These can be mixed with just enough powdered clay and water to hold them together.
It is the air contained in the mix that provides the insulation. The clay only acts as a binder.