Oven: basalt * Insulation: pumice

[v12spirit]

Re: Oven: basalt * Insulation: pumice

Basalt is an igneous rock, but that doesn't automatically qualify it as a suitable oven material. Basalt would make a poor oven. Besides being highly conductive, it won't hold up well to thermal cycling....you'll get cracking. Besides that, have fun shaping it. You'll be hard pressed to find a stone that breaks more chisels or wears out diamond blades faster than basalt.

As far as using pumice goes, it works as an insulator sure. But there are better ones like perlite or expanded clay that are easy to find, as cheap, and work better.

Unless you have nothing else to work with, then don't bother with these materials to build an oven if you care about quality and efficiency.

I have always thought of basalt as one of the toughest stones and didn't even thought of any crackings under thermal cycling!!
Besides. There are many houses in my region that are built entirely from basalt. When one enters one of those houses, one can hardly believe that they are NOT air conditioned. They're warm in winter and cool in summer. That put me under the impression that basalt was not a conductive!!
Looks like there are some facts about basalt that are not as I once thought they were.

[stonecutter]

Re: Oven: basalt * Insulation: pumice

Stonecutter,
Is it just cracking under thermal cycling that makes using limestone or basalt as an aggregate work fine, while using them as a building material doesn't?

I think it does, but it also depends on what the stone is composed of. Generally though, I feel the main reason you don't see most stone used like firebrick, is because of all the faults inherent in stone. Like I said, all basalt isn't the same..there may be some out there that would hold up great if you used it as an oven building unit....namely, ones with a higher magnesium or silicate content.

[stonecutter]

Re: Oven: basalt * Insulation: pumice

I have always thought of basalt as one of the toughest stones and didn't even thought of any crackings under thermal cycling!!
Besides. There are many houses in my region that are built entirely from basalt. When one enters one of those houses, one can hardly believe that they are NOT air conditioned. They're warm in winter and cool in summer. That put me under the impression that basalt was not a conductive!!
Looks like there are some facts about basalt that are not as I once thought they were.

It is tough, I wasn't kidding about broken chisels and wearing out diamond blades. I assumed in the original post that basalt units( not cast refractory brick with basalt aggregate) was being considered to build an oven. Also, there may be some basalt out there that could hold up to thermal cycling in an oven, mainly the ones that contain high silicate or magnesium levels. Most of the basalts I have experience with are high in iron, and I've seen them break up from heat when they where used to line a simple firepit.

As far as your observations of stone houses, that's a different application of stone than a small, thin shelled masonry structure like wood ovens. Being mass based, the stone isn't experiencing the same stresses that it would get in an oven. Since the heat is being distributed through a larger area, I feel that changes the way stone responds to thermal cycling...and allows you to use stone that would break apart in a thinner shelled build. An example of this is the massive limestone oven in Tractormans thread.

[v12spirit]

Re: Oven: basalt * Insulation: pumice

Thanks stonecutter for the details,
I hope there is a heuristic way one can find out the components of the stone (iron, magnesium,..) like color, structure, or even geographic classifications. I live in southern Syria where basalt is plentiful and free.
BTW: Regarding pumice, provided this is a right descending order of insulators (Calsil board or IFB, Vermiculite, Perlite). Feels like pumice comes right after Perlite, or does it?

[stonecutter]

Re: Oven: basalt * Insulation: pumice

Thanks stonecutter for the details,
I hope there is a heuristic way one can find out the components of the stone (iron, magnesium,..) like color, structure, or even geographic classifications. I live in southern Syria where basalt is plentiful and free.
BTW: Regarding pumice, provided this is a right descending order of insulators (Calsil board or IFB, Vermiculite, Perlite). Feels like pumice comes right after Perlite, or does it?

You have access to plentiful and free basalt? I think those are a couple of great reasons to build an oven IMO. Who cares if it lasts? Like I said, maybe the mineral content of your basalt will lend itself to successful firings.

I can't say where pumice ranks against other kinds of insulation, I haven't tested it or even used it. It is more dense than perlite or vermiculite, so I would guess that pumice would not have as great of r-value. Again, if you get it free or cheap, why not try it.

I always advocate using the best possible material or employ the best possible techniques, but try not to be so rigid as to discount alternatives to either. The only time I do is when you are building an oven for a commercial venture or for a client.

[v12spirit]

Re: Oven: basalt * Insulation: pumice

Yes that is why I thought of those materials. I find them in my garden, in the farm, on the way.. They just need one to pick them up and collect them. I will be seeing how I can start collecting them.

[Wiley]

Re: Oven: basalt * Insulation: pumice

Just as an aside, here is a photo of 13 tons of quarter minus basalt I had delivered today. It looks like a larger grain size because when it is wet it had a natural tendency to clump together. While this is a warm spring day the stuff came from a large pile wherein it was wet inside. This is the Pacific Northwest where water is plentiful and rain common.

I am using the quarter minus as underlayment for foundation and leveling beneath red bricks (pavers) for a patio around the WFO (which I'm finally getting around to building). It packs tightly and makes IMHO a better foundation than straight sand. Any left over will be used on the parking area.

Bests,
Wiley

[Tscarborough]

Re: Oven: basalt * Insulation: pumice

Any stone is not really suitable for a high temp oven. Any monolithic structure is going to crack, but one made of a natural stone will also flake and spall. On the other hand, using natural stone as an aggregate is pretty much a necessity. So long as it has thermal characteristics similar to the matrix material it should not be an issue.

Obviously in the past, and even today, an oven can be built with sub optimal materials and they will work. How long and how well will only be determined empirically. I would never consider using less than the best I can afford in my current situation, but in the past I have certainly done so. The best rule is: Build to your budget and the value of your time.

[stonecutter]

Re: Oven: basalt * Insulation: pumice

Any stone is not really suitable for a high temp oven. Any monolithic structure is going to crack, but one made of a natural stone will also flake and spall.

Ah, but with one exception, soapstone. Though if there is heavy veining, it will likely crack.