To construct an oven that stands the test of time you need to understand the effect of heat cycles on the materials used in the oven, combined with the elements.
- What happens with thermal expansion
- What steps are taken to minimise the effect of thermal expansion
- What effect does moisture have on an oven
Thermal expansion is what happens to the materials in the oven through the process of using it. From cold to hot and back to cold again. This process puts stress on the materials. These are the steps that we take to minimise the effect of thermal expansion on the ovens we build. This is divided into three areas, the inside/working part of the oven that gets very hot, and the outside which is there to protect the inside. In between the two is the insulation.
The inside or working part of the oven is where you will find all of your refractory materials. These materials need to be able to co-exist together. What this means, is the expansion rate of the different materials used need to be extremely similar. If there is a miss-match, the oven will break itself into pieces.
The working part of the oven is completely covered with insulation. This includes the dome and the underneath of the floor, keeping the heat contained in the working part of the oven.
The materials used on the outside of the oven are not refractory as the expansion is greater. Keeping them as cool as possible will reduce the expansion. This is achieved through the use of ceramic insulation. It is very important that the expansion of the outer materials do not transfer through to the internal materials.
Moisture is an ovens worst enemy. If the oven is wet, you will never achieve a consistently high level of performance. The outer part of the oven serves as a protective layer to the insulation and the working internals of the oven. This is where having a well insulated oven reduces the stress of expansion in the external shell. Less stress equals less cracking which leads to less water ingression.
Do your research as ovens are an investment. And a wood fired oven should last a lifetime. Where possible witness the oven working, read reviews.