cob oven: perlite or sawdust for insulation?

I'm building a cob oven and trying to decide what to use for the insulation layer. Sawdust is free ... is there a compelling reason to use perlite?

Patrick Mann wrote:
I'm building a cob oven and trying to decide what to use for the insulation layer. Sawdust is free ... is there a compelling reason to use perlite?

It depends on how you are going to use it. If you are mixing sawdust with the clay (or cob) to make an insulating layer, that can work. If you are filling a void with just sawdust, it won't. The sawdust in the clay may burn out but the voids left are still insulating. Perlite won't burn and so is more flexible.

I'd mix either materials with clay slip. Some people seem to have a preference for one or the other and I'd like to know why. It's more important to me to get max insulative value than to save a bit on the materials.

Hi Patrick
The group I worked with used lots and lots of finely chopped straw mixed with pudding consistency clay slip.
The few reports I've had of the oven is that it fires up hot and decreases its heat evenly.
ahhh..playing with cob/clay is so much fun
Enjoy