From: "TAYLOR,DON"
To: 'Jim Buckley'
4/3/03

Jim:
I talked with someone back in Ohio this morning to confirm the attached previous request for information. Nice folks. However, I have also found some interesting information from another oven manufacturer and I would like your perspective.

The direct quote is as follows:
"I have seen the Superior Clay oven product at our annual Masonry Heater Association meetings in North Carolina. It is relatively light weight and some of the components are modified clay flue tiles. I am not sure what testing has been done on it for its durability under fire. Clay flue tiles can often shock and crack from fire if the fire is suddenly hot as in a chimney fire. I have an experimental clay flue tile (veneer) in my office which I love, but it cracked on the day I pushed the exterior temp to just over 250 degrees F."

My concern is that I will be using this oven once or twice every two weeks, and with the intermittent heating and cooling this could cause a problem, with temperatures of 750 degrees being reached on an initial firing of the oven.

My questions are:
1) Is this guy blowing smoke?
2) Do you have any installed sites, or contact lists of owners, somewhere in the San Francisco area where I could see one of the ovens in action or talk with the owners? I have checked with my dealer, but his first response was that he "didn't know", and I would have to talk to a mason.

Any comments or help on this will be greatly appreciated.

Regards,
Don Taylor

    Don,

    The Superior Clay oven built at the MHA workshop in NC was a prototype and is pictured at http://www.rumford.com/oven/wildacres.html. It did have a tunnel entrance made from round clay flue pipe. The current oven, shown at http://www.rumford.com/oven/oven36.html features a new refractory clay entrance tunnel.

    Nonetheless, I think it's a fair question. The white fireclay (refractory) pieces perform better under thermal shock conditions that the shale clay used for flues because it is stronger and better able to withstand weather. But any clay or cast refractory piece is likely to crack if heated or cooled too fast. The trick is not to subject it to sudden thermal shock.

    Our clay ovens, including the ones with shale clay entrance tunnels, will stand temperatures well over 1,000 degrees F without cracking if you heat them up slowly and evenly. Don't induce a chimney fire. And I'm not sure what your masonry heater guy means by the experimental flues in his office but possibly he used the flues to make channels for his heater which might have been heated rapidly to a temperature much higher than 250 degrees if his objective was to get the outside of the heater up to 250 degrees. Don't know. Masonry, even exotic refractory masonry, cracks if heated too fast.

    If the components of any oven do crack, you might ask, what is the consequence? The pieces probably won't fall out due to the shape of the oven. And you can repair the crack if you like but it's probably not necessary. The other imported oven built at the MHA workshop came in sections like an orange - pre-cracked you might say - which isn't a bad strategy.

    I don't know how our ovens are performing. The ones I know about are on line linked to http://www.rumford.com/oven/links.html Some of these are also prototypes and not all our customers were pleased with the"fit" but so far none have complained that the oven cracked. I will contact some of them to see how they like them and let you know.

    Best,
    Jim Buckley

From: "TAYLOR,DON"
To: 'Jim Buckley'
Cc: mcclave
Subject: RE: Fw: Oven materials information request
Date: Thu, 23 Jan 2003

Jim:

Thank you very much for your timely and candid reply. I understand better now how materials are classified and used in food type ovens. I intend to work closely with my local distributor to answer any additional questions. As a side note, I found your website and material to be more helpful for construction information than any other site. If you plan a demonstration or installation class in California I would be interested.

Thank you again for your time and information.

Regards,
Don Taylor

-----Original Message-----
From: Jim Buckley [mailto:buckley@rumford.com]
Sent: Thursday, January 23, 2003
To: Don Taylor
Cc: mcclave
Subject: Re: Fw: Oven materials information request

Don,

Todd has asked me to respond to your email. I will try to address your questions as you ask them below.

Best,
Jim Buckley

----- Original Message -----

Todd:

I am planning to build a wood fired baking oven and there are a few different distributors (and types) of ovens on the market today. I am interested in the Superior Clay Bake Ovens (36" model). However, I have a few questions and would like any assistance you could provide in answering them.

1) What materials do you use to create the oven? I know there are differing types of clay and refractory cements that I have seen advertised. If you chose a specific type, why?

    Our ovens are all vitrified fireclay - the most pure and refractory clay, used for centuries for ovens, kilns and fireplaces. Some of the other ovens are made with cast refractory concrete which is a good product but often has various metals incorporated in the formula which is why some of the oven manufactures deem it necessary to get some sort of listing to assure their customers their ovens are safe to cook food in.
Here is a detailed explanation of reasons for materials and functionality from Mugnaini as an example.

http://www.mugnaini.com/ovens/ovens_resid_features.html

    My point above made for me. "Cotto Refrattario" sounds like "fireclay" in Italian to me. And the rationalization below about the "alumina content" is unnecessary if the oven floor is made with pure fireclay firebrick as ours is.
2) What is the thickness of the bake oven? I have notice that some range from 2" to 4" in thickness. Does this make a difference, if insulated, for start up times? Heat retention? See article above.
    We agree with the comments and hedges in the article. More mass takes longer to heat up but stays hot longer. We've heard complaints about our ovens as well as other ovens about how long it takes to heat up - never a complaint that it heats up too quickly. Of course I suspect the ones that take a very long time to heat are not properly insulated and the oven walls may conduct heat away into a massive brick chimney. We recommend a total of 8" thick oven walls which include a couple of inches for our oven dome and a couple of more inches (maybe) for a brick backing and at least two inches of insulating refractory concrete. This may be conservative and you may want to consider eliminating the brick back-up but, if the oven is inside the house or near combustible material, the code that most appropriately applies is the masonry fireplace code which requires fireboxes to have 8" thick walls and be kept 2" clear of combustible material.
3) Is there any warrantee with your product?
    We are a reputable company and stand by our products to be as advertised. In addition all our products meet appropriate ASTM standards for firebrick, refractory mortar or clay flues. I'm not aware of any materials standards for clay oven components. Having said that, there is ample opportunity for any clay component to crack as a result of abuse or thermal shock. Probably a crack or two won't hurt but you should break in the oven with a slow fire at first and never subject it to a sudden overfire condition or cool it down too fast by throwing water in or on it.
4) Do you offer, or make, larger fire brick for the baseÊor floor of your oven? I would like something at least 1 ft. square and 2 inches thick.
    Larger firebrick - at lease 8"x8" - are available but cost more. We can also provide 18" or 24" castible refractory slabs used for kiln furniture but they are made with exotic materials and you run into the issues of "alumina content" mentioned above and we have not had these materials tested for use as a cooking surface. We could also provide soapstone, which would be a good natural stone refractory surface but even soapstone is likely to crack if the blocks are too large. We decided to stick with firebrick. You could bevel and smooth the edges a little.
5) Do you have any competitive information about how your oven compares with Mugnaini (http://www.mugnaini.com) or Earthstone (http://www.earthstoneovens.com)?
    No. I think those are both good companies. We're all in the 2,500 year old Roman tradition of semi-spherical earthen oven design, changed not very much over the years in Italy, France, Mexico and Virginia. Ours are all clay and in some ways the most traditional, while Muganaini and Earthstone have been at it a little longer, sell larger commercial ovens, have more well developed literature and cost more.
6) Do you have pricing information on the larger oven (36") and what comes with the kit. Thanks in advance for any information you may be able to provide. It will help me with my purchase decision.

Regards,
Don Taylor

Sent: Sunday, April 20, 2003
To: TAYLOR,DON

Don,

We've had no report of cracked oven domes, although I wouldn't be surprised if they would crack if fired too fast. I think Alan Scott's method of building a fire in an oven would result in a slow and steady increase in temperature that would not damage the oven. On the other hand, most refractory materials crack but it's not a problem. Due to the shape of the dome, if it did crack, I would expect the pieces to stay put. Most ovens, including ours, are made in several pieces - pre-cracked if you like.

I don't personally know of any of our ovens in the Bay Area. Our new designs have only been available for about a year and maybe there are none in the Bay Area. Let me refer you to Mitch at McNear Brick (415 454 6811) however. He may know of an oven.

I'd be interested in your report upon trying Alan Scott's oven - the others as well.

Best,
Jim Buckley

Jim:

Thank you for your reply regarding the oven dome cracks. I had suspected as much, with the information I have recently read and found in talks with other manufactures. The cracking doesn't seem to be a real issue the more I looked into it.

I had a great time baking some whole wheat sourdough loaves last Thursday in Paradise. The oven was already fired (it took about 3hrs from cold to get it up to 550 degrees by the time I arrived. I found this interesting, since most of the the other oven masses are up to temperature and ready to bake within 45 minutes to one and a half hours.

I have noticed that the masses for most of the other ovens range from 2.5 inches to 4 inches.This is the major difference between the other ovens and Superior Clay oven. Is it recommended to "lay on" a heavier thickness which would provide that thermal mass? Is there a recommendation on the type of material to build the mass up without having a problem with dissimilar materials expanding differently? It would seem to me the heat could cause a problem in expansion or friction between the clay and any other material like Portland cement.

My goal is to be able to do a shorter fire (fuel efficiency), bake some pizza and then bake some bread (5 or 6 loaves). I am sure that this would work with the standard product and some insulation material (pearlite or vermiculite), but I also though for longer term roasting it would be good to add an additional 2 inches of insulation.

Am I making to much out of this cladding issue?

Regards,
Don

From: Jim Buckley
Sent: Monday, April 21, 2003
To: TAYLOR,DON
Subject: Re: Oven cracks and other facts...

Don,

We agree that 2" to 5" is probably about right for oven wall thickness, depending on how fast you want the oven to heat up - and cool down.

We make our oven walls a total of 8" thick only because we have no listing or test numbers to indicate otherwise so we are trying to stick to the building code requirement that "firebox" walls be at least 8" thick. Let me point out, however, that the 8" could be made up with as little as an inch or two of high density masonry (our dome and/or firebrick) and the rest of the thickness could be made up of DeltaCrete, an insulating castable refractory.

How long does bread take to bake? I wouldn't advise making the oven walls so thin that it cools off too fast and I would think it might cool off about as fast as it heats up.

I'm enjoying the vicarious experience of shopping with you. Please let me know which oven you decide is better and why even if it's not ours.

Best,
Jim Buckley

Don Taylor On Baking in an Alan Scott Oven
4/16/03

Jim:

Thank you for your reply. I suspected and now know why William Rubel (author http://www.williamrubel.com) said you were wonderful to work with and a wealth of information. He references you on his web page.

[The oven Don tried was "an Alan Scott oven.. or similar based on the basic construct of using fire brick for the interior. Similar, but not exactly the dimensions used in the Bread Builders Book". The oven was "about 36 deep x 35 or 36 wide" with walls about 8 inches. From cold to 550 degrees the oven took about 3.5 hours to heat up.]

The bake time for the loaves of bread (6) at hearth temp of 545 degrees took a total of about 20 minutes. Prior to the bake, she added moisture to the oven after mopping out the floor and placing the loaves. After the first 5 minutes the baker moved the loaves, checked temperature, and added moisture to the oven by spraying in water on the ceiling and back of the hearth, and then closed down the oven for the remaining 15 minutes. This dropped the temperature to around 520 or so and after a few minutes the oven recovered to about 525-530. When I asked the baker how many bakes she could get in a firing she told me that she had only done about 15 pizzas, 3 separate bakes for bread and then roasted six chickens. A total bake time of around 3.5 hours. She said that the oven cools slowly and you could do a slow cook on some lamb or something that requires slow low heat. In fact, she said that late the next day she throws some wood in the oven after it is down to about 150 degrees to dry it out for her next weeks bake.

If she has fired up the oven one day, and starts to refire the next morning, it retains about 50% of the peak heat as long as it is closed up. People who bake regularly only have to have a short burn (30-40 minutes) to bring the oven back to temperature.

Now, I understand this because Alan Scott ovens are designed to retain that heat in the thermal mass. I have heard rumor of one guy who had a marathon 16 bakes in a session! Maybe it is folklore, but none the less, you get the idea of the thermal mass in a Scott oven.

I will be happy to share my experiences. I am trying to figure out how to do the masonry work myself, so I am building a test oven from scratch this next month (Sunset plans modified). I want to make mistakes on something that I will not have to live with!

Thanks again for the information about the cladding. I will plan to have the full 8" of insulation for building codes and investigate the DeltaCrete material. It would be interesting to embed some thermocouples in the hearth and dome joint to take readings. I'll consider that when designing the oven layout.

Regards,
Don

Thanks, Don. That's an interesting and instructive lesson on baking bread. Was that an Alan Scott oven? How large was it? How thick the wall? How long did it take to heat up? Sorry, I lost track.

Jim

Jim:

Sorry... I write too much... as they say here (TMI) To Much Information! Was that an Alan Scott oven? Yes, or similar based on the basic construct of using fire brick for the interior. Similar, but not exactly the dimensions used in the Bread Builders Book.
How large was it? As a guess about 36 deep x 35 or 36 wide.
How thick the wall? 1 fire brick thick with a cement cladding + vermiculite (sp?) fill making it about 8 inches.
How long did it take to heat up? From cold to 550 degrees about 3.5 hours A good website to see how one of these is built can be found at: http://mha-net.org/msb/html/bakeov16.htm

Hope this helps.
Regards,
Don

[Ovens] [Endorsements]

Buckley Rumford Fireplaces
Copyright 1996 - 2010 Jim Buckley
All rights reserved.
webmaster