Volcanic rock

[Nick House]

I am planning to try and build an oven in Indonesia, we have masses of volcanic rock everywhere. Could I use this instead of the fire bricks?

Any help or advice or ideas would be greatly appreciated!

[Johnny the oven man]

Is it the porous type of volcanic rock? I think that type would be more insulative.

[Neil2]

What is the density ? How much does it weigh per cubic foot ?

[Nick House]

Gents

We have all sorts of volcanic rock from a hard granite type to a more soft pumice type. I would have to write to a friend and get them to sort out how dense either or both are. As I live in Saudi it might take a while. Our property is quite remote and so I was thinking that using locally available materials would be preferable especially seeing as I am not sure I could get fire bricks and even if I could I am sure they would be very expensive.

Do you guys think that it would possible to build an oven using these type of rocks?

Thanks for any advice you have, I am a complete novice at this type of thing, and just trying to get some information.

[Tscarborough]

As a rule natural stone of any type is not a good choice for the direct fire portion of your oven. Low fired adobes or common solid brick would be a better choice. They may not last as long as firebrick, but they will suffice and both are cheap and available everywhere.

[Nick House]

Thanks for the info. I will bear all these things in mind. I am tempted to experiment a bit before I finally decide what to do. Why is generally a bad idea to use natural rock?

[dmun]

Hard stones (We're exposed to granite in the states) have a reputation for cracking and spalling (surface chipping) when exposed to direct flame. That said, so do common bricks, so there might be no real reason not to try them, if there's a reasonable way to cut a hard volcanic stone like basalt.

[Lburou]

Volcanic rock runs the gamut in specific gravity, from heavy basalts to light pumice. The stone resultant from a light and frothy expulsion from a volcanic eruption has more trapped air (read more insulative capacity) that might insulate better than a more dense rock. Either way, the rock will be strong but brittle.

You can build the oven from volcanic rocks, but will likely not have much stored heat energy or insulative affect. But, practicality is king in the remote areas you describe too. You may find some local wisdom in the villages for outdoor cooking....Hopefully a small price to pay for living in paradise

Decomposed volcanic soils become clay eventually. Clay may be available depending on the age of the eruptive materials, you could use that some way I'm sure.

Good Luck

[Nick House]

Thank you, I am slowly understanding more and more of the posts. And understanding the importance information in something like this. But in the end I am sure that a bit of practical experimentation is what is really required. What would be the best way to experiment?

[dmun]

I think lburou's suggestion of tapping into local knowledge is a good one. What stone or material is locally used for fireplaces or cooking?

As far as actually using volcanic rock, I would ask, how is it used locally? Is it available in blocks or sheets?