FibraMent vs. Cordierite (Engineering Data)

[November]

FibraMent
Density: 1.762 g/cm³
Thermal Conductivity: 0.69183088225 W/m-K
Maximum Temperature: 538 °C
Strength
Flexure: 10.58345 MPa
Compressive: 73.29127 MPa

Cordierite
Density: 2.6 g/cm³
Thermal Conductivity: 3.0 W/m-K
Maximum Temperature: 1315 °C
Strength
Flexure: 117 MPa
Compressive: 350 MPa

Note: Strength properties were evaluated using slightly different ASTM standards, however the standards are similar enough in their test specifications for the purpose of this comparison.

For a thermal shock resistance comparison, the following is an approximative extrapolation based on the simplified formula R_s = (thermal conductivity * flexture strength) / (coefficient of thermal expansion * modulus of elasticity).

FibraMent: 73.5
Cordierite: 500

As hard as I tried, I could not work out a result that gave FibraMent a more favorable thermal shock resistance value.  The large, unwavering disparity between the two materials rests mainly in the thermal conductivity.  I almost don't want to trust the FibraMent manufacturer's numbers.  They mentioned using ASTM C177 which is BTU-in/hour-foot²-°F, but they could have mistakenly meant BTU-foot/hour-foot²-°F, although I seriously doubt it.  I'm inclined to believe that, because the maximum operating temperature difference between them is greater than twofold, and the density difference between them is almost 1.5x, cordierite really can take more thermal punishment than the FibraMent.

Maryland Ceramic & Steatite Company Inc. is quoted as saying, "corderite has excellent thermal shock resistance, withstanding red heat to ice water quench, and then returned to red heat. Our high fire corderite body will withstand a temperature rise from 70° to 1800° in 80 seconds, followed by an immediate room-temperature air quench."  That seems to substantiate the large difference between FibraMent and cordierite thermal shock resistance.  FibraMent can't even reliably reach 1800°, let alone be air-quenched from that temperature.  I'm sure the decision to buy one material over the other will still be influenced by several other factors, but at least this gives the curious mind an idea of the performance differences based on engineering data.

- red.november

[November]

The two cheapest places I could find round FibraMent and cordierite stones manufactured specifically for pizza baking, each measuring between 15 and 16 inches in diameter, were:

FibraMent (15.5" x 0.75") - $44.95 Total
http://www.theposhpeddler.com/awmco_15in_round.htm

Cordierite (15.75" x 0.875") - $39.61 Total
http://www.abestkitchen.com/store/pizza-stones.html
Note: The thickness listed at the above website is incorrect.  The thickness is indeed 0.875" per the manufacture.

[Pete-zza]

November,

I have a rectangular (14" x 16") baking stone from Old Stone Oven and it has pedestals, or "feet", on the bottom side. If the feet are included in the thickness measurement, the "total" thickness is about 7/8". If they are not so included, the thickness is close to 1/2". I checked the American Metalcraft website but I couldn't find anything to tell me whether their Cordierite stones also includes feet. If they do, would that alter your analysis? My Fibrament stone does not have any feet.

Peter

[Pete-zza]

November,

This is a case where a photo does a better job than words.

Peter

[November]

Peter,

I would be very surprised if the American Metalcraft stone possessed feet.  I have seen the product listed numerous (6+) places, and not one of them mentions feet.  It's fairly clearly shown that the stone does not rise above the surface it rests on in the following picture: http://www.amnow.com/pizzaSupplies/images/pizzaStonesSTONE13.jpg

The analysis was based on the materials, not specific end products.  Whether the stones have feet or not, the engineering data remains exactly the same.

- red.november

[Jack]

Nice comparison Nov.  I just hate seeing those numbers when I own a Fibrament. 

In day to day usage though, I'm not sure that I'd want the Cordierite.  The Fibrament takes long enough to pre-heat and I use it well within it's operating specifications, although I did make a real leadball pie a few months back that may have pushed the limit on compressive strenght. <grin>

On a positive side, is it also a cementicious product?  When I have not used my Fibrament for a while, here in the damp PNW, my wife will sometimes complain about the "wet concrete" smell, as it is pre-heating.

Jack, WA PE Mechanical

[Pete-zza]

I would be very surprised if the American Metalcraft stone possessed feet.  I have seen the product listed numerous (6+) places, and not one of them mentions feet.  It's fairly clearly shown that the stone does not rise above the surface it rests on in the following picture: http://www.amnow.com/pizzaSupplies/images/pizzaStonesSTONE13.jpg

November,

When I originally went to the American Metalcraft website and looked at the AM stones, at http://www.amnow.com/pizzaSupplies/pizzaStones.html, I saw two photos. The top photo was the same as the one you referenced in the above link. Clearly, there are no feet on the pizza stones shown in that photo. But the photo below that one, for baking stones, suggested by the shadowing that possibly those stones had feet. Although the answer to the question of feet or no feet will have no effect on your analysis, it might be of interest to those who are looking for stones and want to know exactly what they are getting. To satisfy my curiosity, this morning I called American Metalcraft and spoke to a customer service rep. She said that the stones designated "Pizza Stones" are 5/8" thick (you will note that no stone thicknesses are given for the "Pizza Stones"). You will also note that the Pizza Stones are specified as being of a ceramic material, not Cordierite specifically. However, the "Baking Stones" are of Cordierite. When I asked whether the Cordierite Baking Stones had feet, she couldn't find anything in her computer to provide an answer, so she referred me to the warehouse manager. He said that the Cordierite Baking Stones do have feet. That is why two different thicknesses sometimes appear in the ads. When I thought back, I couldn't remember any ads for my stone mentioning feet either, and the only thickness dimension that I could recall in the ads was around 7/8".

Looking at the prices shown for the American Metalcraft Pizza Stones and Baking Stones at the AM website, the Baking Stones seem to be the closest to my stone in composition and in price (although I paid less than the comparable price shown at the AM website).

Peter

[November]

Peter,

Thanks for calling to find out for sure.  I had thought that the pizza stones and baking stones would be made similarly.  That's why I referenced the photo of the pizza stones, and because the drop shadows on the picture of the baking stones look like they were added in post production.  Those are not natural looking shadows for being projected onto an underlying surface just 0.25" inches away.  The distance between the corner edge of the shadow and the stone is at least the thickness of the stone which can't be right, so I just ignored those photos.  The stone I was referring to in the pricing post was the PS1575 product.  What's sad is that nowhere is it mentioned that the product has feet.  It's almost pointless to provide a dimension when it's just a surface feature that protrudes to that depth.

The best deal on cordierite may still be from a kiln shelf supply store such as Sheffield Pottery, but 0.625" isn't bad.

- red.november

[Art]

Please don't shoot the messenger, but I am posting this response I received from a spokesman for the Fibrament folks. I thought it only right someone there had a chance to present their data.     Art

"I am disappointed to learn red.november used incorrect data to evaluate our FibraMent Baking Stone. It is apparent this person does not have the knowledge or academics to correctly compare our FibraMent Baking Stone to the ceramic cordierite.
 
FibraMent is specifically manufactured for commercial and home baking stone use. Cordierite is primarily used as kiln furniture and for applications in steel mills and foundries. Cordierite is available in many formulas. What grade of cordierite did red.november use for his evaluation?
 
We send our FibraMent Baking Stone to CTL in Skokie, IL for testing. They are internationally respected testing laboratory. The heat transfer/thermal conductivity rating (k factor) for FibraMent is 5.6 Btu. in./hr. sqft. F. I do not know why red.november would dispute the lab's results.
 
It is common knowledge in our field that higher density materials have lower thermal shock values. The dry density of our material is 126 lbs pcf.
 
To increase FibraMent's strength we place several layers of high temperature fabric in the matrix. Cordierite does not use any type of fiber or fabric to increase its tensile, flexural or compressive strength.
 
The Compressive Strength for FibraMent is 10,630 psi per ASTM C 109. Our Flexural Strength (Modulus of Rupture) is 1535 psi per ASTM C 78. Compressive Strength does not have anything to do with heat transfer.
 
red.november also has the maximum temperature rating for FibraMent incorrect. It appears red.november is only trying to discredit FibraMent. The maximum temperature rating for FibraMent is 1500 F/815 C. The maximum temperature rating is independent of heat transfer. Baking stones are typically used at temperatures from 350 to 600 F. It is not necessary for baking stones to have a temperature rating that exceeds 750 F.
 
Thank you for bringing this to my attention. Please feel free to post my reply on that web site.
 
Mark

[November]

I would expect no less a defensive response from the manufacture if given the impression that someone were trying to make them look bad, but what I want to know is what did Art tell them to give them that impression.  I have no ulterior motive here as I really don't care which material is better, and I did use their published data which can be found here:

http://www.foundryservice.com/Fibrament%20Data%20Sheet.pdf

If their data has changed since then, they should have their data republished instead of pretending like the data that's out there is bogus.  It seems clear that the representative doesn't understand the nature of the comparison either.  Yes, the strength of the material has nothing to do with heat transfer, however it determines in large part the thermal shock value which was one aspect of the comparison.  Anybody with a primitive understanding of material science gets this.  Further illuminating the representative's lack of understanding is his/her need to point out the strength values, as if what I listed was incorrect.  For those of you who don't want to bother with the conversion, I assure you 10,630 psi = 73.29127 MPa and 1,535 psi = 10.58345 MPa.

So their new thermal conductivity value might have risen to 0.8071360293 W/m-K, and the density increased to 2.018 g/cm³ on a later revision based on the representative's response.  I would like to point out the obvious here and state that their thermal conductivity is still pretty distant from 3.0 W/m-K.

I appreciate seeing the most current data they have to offer, but I don't appreciate being setup as if I was malicious in my comparison.

- red.november

[Art]

I told them nothing that would give them the impression that you or anyone was trying to make them look bad. I simply emailed the link to this discussion. I assure you there was no "setup" here.  Art

[November]

Art,

Would you then be so kind as to ask them for their product's coefficient of linear thermal expansion?

"It is common knowledge in our field that higher density materials have lower thermal shock values." is an over-generalization.  There are two kinds of densities in play here.  The density of the compound, and the density of the structure.  Smaller grain size (i.e. higher structural density) has a positive impact on thermal shock resistance.  That is what is common knowledge within the ceramics industry.  It would make sense to anyone who understands thermodynamics since higher structural densities typically support higher thermal conductivity.

Knowing the coefficient of linear thermal expansion would remove the need for extrapolation, and make density a moot point, other than higher densities can hold more heat that is; and holding more heat is generally accepted as a good thing for baking stones.

- red.november

[abatardi]

Isn't this like trying to decide whether a McLaren or an Enzo Ferrari would make a better 25mph turn? 

- aba

[2stone]

visual data

[abatardi]

looks awesome - what are the toppings (mushroom, sausage?)?

[2stone]

roast beef and caramelized onions

what a meal!

[Jack]

Isn't this like trying to decide whether a McLaren or an Enzo Ferrari would make a better 25mph turn? 

- aba

Maybe a little.  The technical differences are sufficiently valid to be debated.  Similar looking/sounding materials can often perform hugely different in different environments.

Nov said "and holding more heat is generally accepted as a good thing for baking stones", although this statement could be debated too. Personally, I'm thinking I'd like my stone to transfer and absorb heat pretty easily too, unless his statement was only with respect to heat capacity.


Jack

[vitus]

Sorry if this is a stupid question:

When you guys say Cordierite, are you then talking about a natural occuring mineral or an engineered composite material (like FibraMent)? Could I for example get my local stonecutter to cut me a slice of Cordierite to use as a baking stone? 

[November]

Nov said "and holding more heat is generally accepted as a good thing for baking stones", although this statement could be debated too. Personally, I'm thinking I'd like my stone to transfer and absorb heat pretty easily too, unless his statement was only with respect to heat capacity.

Jack,

You just needed to quote more of the statement.  What I said was:

higher densities can hold more heat that is; and holding more heat is generally accepted as a good thing for baking stones.

I am indeed talking about heat capacity relative to density, not to be confused with specific heat capacity which factors out volume (and consequently half of what defines density).  Even if two materials had the same specific heat capacity, the higher density material will have a higher heat capacity per volume.  That certainly isn't debatable.

- red.november

[November]

When you guys say Cordierite, are you then talking about a natural occuring mineral or an engineered composite material (like FibraMent)? Could I for example get my local stonecutter to cut me a slice of Cordierite to use as a baking stone? 

Cordierite is a mineral, but it's also engineered as a ceramic.  One example of engineered cordierite might also include mullite.  You can get a stone cutter to supply you with a slice of cordierite, but I imagine a ceramics supplier would be less expensive.

- red.november