Insulation alternatives

[james]

I guess the world is getting smaller. Yesterday I rec'd photos of a Pompeii oven in Sweden, and today I heard from a gentleman building a Pompeii oven in Tailand. It sounds like you can't find vermiculite there, so I wanted to ask if anyone has had experience using old-world insulators. I have heard that ash, or an ash and sand mix makes a good insulator for around the dome.

Any thoughts on that?

As an experiment, I covered my first precast oven in San Gimignano with sand, then an inexpensive insulation blanket -- with mixed results. Sand has a lot of thermal mass and it really heats up, so the oven was so-so at holding heat inside the chamber, and the stucco shell got hot.

What are the properties of wood ash?

Alf, you use sand in the large commercial bread ovens...right?

James

[Alf]

Yep we use sand in the large commercial ovens we build for several reasons, 1) It is a good heat sink, is easy to come by and place on top of the ovens arch 2) Sand allows the oven arch to flex during odd commercial firings 3) We often have flues and water heating on top of these ovens and sand allows for movement and transfer heat efficiently.

I wouldn’t say sand is a good insulator, however, that’s what folks used in the past. I have read that charcoal is a good insulating material along with crushed glass. One of the best insulating materials is still air of vacuum, so wool, straw, hay, bracken (one would have to check about combustion) shells from shellfish etc, or any natural material that will trap and hold air would be good

One other good material if available would be polystyrene from packaging.

Alf