Oven: basalt * Insulation: pumice

[stonecutter]

Re: Oven: basalt * Insulation: pumice

Uh...I typed a reply and it has vanished.


Anyway the short of it is that I'm not disagreeing with using crushed basalt as a gauged aggregate, just as an oven building unit. I'm not sure that was the intent anyway. And I never said I don't like basalt..it makes a fine wall, and even though it's very hard to shape, it makes beautiful sculptures and polishes like glass.

Also, there are several different kinds of basalt. Some possess refractory minerals like silica and alumina, others contain stuff like sodium and iron. So it would be beneficial to know what you are using, because all natural stone within a specific group, has lots of variance in composition and mineral make up. As an aside, what source says basalt is amorphous? I've never heard that reference to any rock other than gemstone.

I don't disagree with using it as thermal mass over a steel shell either. You can use almost anything that doesn't degrade or burn....even quartz sand. There is a lot of material used as aggregate or even a pozzolins, that could not hold up to thermal cycling on their own as a unit.

I'm interested in mix design and I'm developing a couple right now. I was wondering..... Are the commercial ovens using the basalt mix as a castable or only as thermal mass? How old are they and what is the condition?


Edit: I just skimmed through your build. That is a very cool oven!

[Wiley]

Re: Oven: basalt * Insulation: pumice

OK, so I didn't want to start some sort of fight. Stonecutter obviously doesn't like basalt and seeing as how he uses stone he obviously knows what he is talking about using basalt en masse with chisel and hammer. However, using crushed basalt as the sand and aggregate in a concrete mix is a different story IMHO.

Unlike common sand, which is usually comprised of lots of separate distinct minerals, crushed basalt is quite homogenous. Basalt is amorphous, meaning it is uniform in composition. Crushing it simply makes smaller particles of the same material, each with the same physical characteristics as the other. There is only two materials to present problems: the differential of expansion of the calcium aluminate and that of the basalt. So far empirical data would suggest they are very close as the half brick is very much as it was six years ago in spite of neglect and abuse from fire and the elements.

I have taken a couple of photos of some left over quarter minus in a pile. I have also taken a small rectangular trowel and tamped down a small area so one can see how closely it compacts. The space between the pieces would be filled with calcium aluminate cement if one were making concrete of this material.

A basic simple formula for home mixed concrete is one part cement, two parts sand and three parts larger aggregate (stones). This mix is commonly called a 1-2-3 mix. It's easy to remember and it is the reason I decided to use one part calcium aluminate cement to five parts quarter minus crushed basalt. When one says quarter minus one means anything larger than 1/4 inch will be screened out while everything small passes thru the screen and into the quarter minus pile. The range from the largest pieces to the stone dust I accepted as the sand and stones (the 2 parts sand + 3 parts gravel making 5 parts) in a 1-2-3 mix. No special reason it looked right and looked like it would work.

It does. It is easy to work and shape into complex shapes. The very fast cure time is both a blessing and a curse. One it allows one to work progressively almost continuously BUT one has to work fast and mixing small enough batches that one has it placed or shaped before it goes off. Using cold water and six quart batches (one quart calcium aluminate and five of the quarter minus just as if came from the pile) made for some fast moving. No breaks for coffee or whatever while working a batch.

Now would I suggest using it? Well I'm most pleased with my WFO and I know of several others built closely on my design. Two in commercial use. My WFO is steel lined with the basalt /calcium aluminate cement refractory as my heat reservoir. I don't have a need at the moment for another WFO and if I did I would build it very close on the design of my first.

v12spirit: check out the thread on firepits I posted pictures of it there years ago. The pit is portable and has been moved several times. Like lots of what I prefer to build it is made of re-purposed materials. Presently it is on the shores of Lake Jeannette (which is what we call our pond).

Bests,
Wiley

[david s]

Re: Oven: basalt * Insulation: pumice

Stonecutter,
When I built my WFO I had some left over 1 part calcium aluminate cement to 5 parts crushed 1/4 minus basalt that I mixed and formed in one of those molds one uses to cast stepping stones. The mold I used created something very close to the size of half a red house brick.

That was about six years ago and that cast extra leftover "brick" has been abused by fire (I have it in the bottom of an outside fire pit...although it is actually a wheel rim) and weather (left out thru snow and rain etc.) The "brick" has held up very well with little apparent degradation.

I would have no problem using that mix as homemade castable for a WFO. As for mortaring solid pieces of basalt together to form an oven I have no personal experience to share but as crushed aggregate held together by calcium aluminate cement it has proven it's stability and durability to me. And as the heat reservoir in my WFO it has worked without problem for six years.

Hope this helps,
Wiley

My refractory supplier tells me it is common for industrial chimneys to be lined with calcium aluminate cement and cracker dust (fine basalt aggregate from dust to around 3mm in size)

[stonecutter]

Re: Oven: basalt * Insulation: pumice

Further, a floor on a firepit is not subjected to the same extreme temperature swings as an oven chamber. In the case of your bricks, you mixed the graded basalt aggregate with a refractory binder. I would not all it a basalt brick or unit.

I'm not against using alternatives to tried and tested refractory material. You just need to understand alternatives are not on par with refractory products.

[stonecutter]

Re: Oven: basalt * Insulation: pumice

Stonecutter,
When I built my WFO I had some left over 1 part calcium aluminate cement to 5 parts crushed 1/4 minus basalt that I mixed and formed in one of those molds one uses to cast stepping stones. The mold I used created something very close to the size of half a red house brick.

That was about six years ago and that cast extra leftover "brick" has been abused by fire (I have it in the bottom of an outside fire pit...although it is actually a wheel rim) and weather (left out thru snow and rain etc.) The "brick" has held up very well with little apparent degradation.

I would have no problem using that mix as homemade castable for a WFO. As for mortaring solid pieces of basalt together to form an oven I have no personal experience to share but as crushed aggregate held together by calcium aluminate cement it has proven it's stability and durability to me. And as the heat reservoir in my WFO it has worked without problem for six years.

Hope this helps,
Wiley

That great, but not what I was talking about.

It's kind of like comparing your basalt aggregate to sand. A large part of which is composed of Quartz. On it's own as a unit or slab, it would not hold up to thermal cycling, yet, it's a usable and lasting component of fire mortar.

[v12spirit]

Re: Oven: basalt * Insulation: pumice

Hi Wiley,
It has been a while. Interested to see your fire pit and those homemade basalt bricks if you care.

[Wiley]

Re: Oven: basalt * Insulation: pumice

Stonecutter,
When I built my WFO I had some left over 1 part calcium aluminate cement to 5 parts crushed 1/4 minus basalt that I mixed and formed in one of those molds one uses to cast stepping stones. The mold I used created something very close to the size of half a red house brick.

That was about six years ago and that cast extra leftover "brick" has been abused by fire (I have it in the bottom of an outside fire pit...although it is actually a wheel rim) and weather (left out thru snow and rain etc.) The "brick" has held up very well with little apparent degradation.

I would have no problem using that mix as homemade castable for a WFO. As for mortaring solid pieces of basalt together to form an oven I have no personal experience to share but as crushed aggregate held together by calcium aluminate cement it has proven it's stability and durability to me. And as the heat reservoir in my WFO it has worked without problem for six years.

Hope this helps,
Wiley

[stonecutter]

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.

[v12spirit]

Hi guys,

Basalt is cooled lava. Where can one find a hotter kiln to bake man made bricks?
Pumice is fairly light and is full of holes that can trap the air. These are the characteristics of an insulator.
What I see above is typical oven-building-materials, don't you guys think?