Igloo design refinement

[laurie]

We have made a few ovens hand cast over sand and the latest is one we made by using large and medium size dog igloo house ,one suspended inside the other upside down forming a 3" cavity, and pouring castable refractory cement into it. We did it in two parts so it was reasonably manageable to handle. So far so good and now we want to apply insulating layer and stucco. Any suggestions about what to use for each of these processes ? Do we need to use lath before we do a brown coat ? What should we use as a mortar between the two parts or do we even need it ? Each piece is very heavy and not likely to go anywhere and I am wondering if using mortar will make it more or less likely to crack. Any input would be appreciated

[david s]

Re: Igloo design refinement

Part of the reason for creating sections is to create cracks where you want them to allow for uneven heat stresses to be accommodated. Most modular ovens suggest mortar only on the outside, to prevent any bits falling into the food. Mortar squished into the joins from the outside and a layer sitting proud of the surface is usually the go. You could use the homebrew recipe or, if you have plenty of castable left, you can sift out the course aggregate and use the resulting mixture as a mortar.The other reason for making it in sections is of course to be able to handle them more easily. They are heavy.
Most people use an insulating blanket, then some vermiculite or perlite concrete, then the stucco.