#11  
Old 12-18-2010, 10:05 AM
Il Pizzaiolo
 
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Default Re: Rock wool as insulator?

Lburou, you are correct with regard to how the floor is set.

I have done a bit of tweaking in the landing area. Initially I built to the exact FB plans; next I replaced the entry with a single slab of soapstone and I found that what I created was a conduit for the heat to flow into the entry, not good. I tweaked things by pulling the entry soapstone forward and adding back a 2” bit of firebrick, things got better. I found that the heat retention returned to what it had been before the entry change. Next I added a profiled slice, a heat break, of rigid ceramic fiber board between the oven floor and the stone in the entry, the soapstone was replaced with granite. The results of this change are that the heat retention was even better.

The transition from the oven into the entry and from the oven into the flue, are most often not insulated and therefore an area that caries heat from the oven. Some here are working on or have built a material break into these areas to retain more heat in the oven. I feel that you can choose to bleed off heat when you need to, so I’d rather have more insulation than less around the oven.

As far as materials; a feature of the soapstone is heat conductivity. This is great for something’s and not so good for others. A good example is pizza stone or the oven floor in a pizza oven. A warning here, the bread baking community using Alan Scott designed ovens, don't feel that soapstone is idea for bread. These ovens have roughly twice the thermal mass than the FB style ovens, my guess.

I feel the the FB design is more flexable with regard to usage. I have though about increasing the thickness of the floor to bring up the thermal mass, but this is more about my curiosity about how the heat curve of the oven will change than a real expectation that this change would benifit my cooking. If I were more dedicated to large bouts of bread baking, then the additional mass would matter. As it is, my 43 inch oven would like to have something like 16 lbs of bread baked at once. The additional mass would come into play on the second and later batches of bread. That's a whole bunch of bread to makeup.. The other aspect of mass is that it will take more time to heat up and so also take more wood.

The firebrick is less conductive than the soapstone and the rigid board insulation is almost a factor of 10 less conductive than the brick.

The advantage of the single surface in the entry area is cleanups are a snap. Inside the oven the firebrick is self cleaning but in the entry spills become a part of the firebrick because of the porous nature of the brick. It also allowed me to make the entry area consistent with the outside work surfaces.

Chris

Last edited by SCChris; 12-18-2010 at 10:39 AM.
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  #12  
Old 12-18-2010, 11:13 AM
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Thumbs up Re: Rock wool as insulator?

Again Chris, you have aided my understanding of this complicated process..Thank you a thousand times for taking the time to share your experience with a newbie

I have moderated several forums on a very busy message board for ten years, and I know that through the years I've grown calloused to the needs of newbies (look for Leeburough -Turbobuick.com forums). I'll have to go back to helping those new people find/discover the same information and processes over and over again, thanks for renewing my commitment to helping the newbies
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  #13  
Old 12-18-2010, 11:20 AM
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Question Re: Rock wool as insulator?

Quote:
Originally Posted by dmun View Post
Mineral wool is the name in Europe for what we call fiberglass insulation, and it has the same problem: organic binders that burn and stink. Make sure what you buy is meant for refractory applications and will withstand 1000f temperatures.
Chris, note the quote above. Its a caution by dmun from another thread about 'mineral wool' not rock wool. Nevertheless, did you notice any of these issues when you fired up your oven with a major amount of rock wool supplementing the ceramic insulation?



Last edited by Lburou; 12-18-2010 at 11:22 AM.
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  #14  
Old 12-18-2010, 12:08 PM
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Default Re: Rock wool as insulator?

I didn't have any negative experience with regard to rock wool/mineral wool, smell or otherwise. Wikipedia indicates that mineral wool is the correct term.

Mineral wool - Wikipedia, the free encyclopedia

This article does indicate "Mineral wool may contain a binder, often food grade starch, and an oil to reduce dusting."


Chris
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  #15  
Old 12-20-2010, 01:39 PM
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Thumbs up Re: Rock wool as insulator?

Found this quote in another thread, but its pertinant here:
Quote:
Originally Posted by BackyardPermaculture View Post
tfasz,

My oven is reasonably small and is not an igloo - it's enclosed. But my insulation worked out significantly cheaper than that:

- A 25 sq ft roll of insulation easily covered my dome/arch once, with enough to cover the top twice.
- Insulation is "Tombo" brand rockwool, made in Indonesia. It has an operating temp of 650c (1200F)
- 2" thick roll, so my dome top has 4 inches over it

The whole roll cost me about $50 from an industrial insulation guy - not sure if it's available where you are, but it works really well and was a great price.
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Old 12-22-2010, 07:18 AM
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Default Re: Rock wool as insulator?

I can not locate the thermal calculator I used a while ago, but I can assure everyone that Mineral Wool insulation is perfect for wood fired ovens. Each insulation has thermal properties different from others and have specific temperature ranges where they are superior to others. Industrial furnaces typically use mineral wool as an insulator next to the "hot face" refractory (the fire brick in our case, ceramic fiber in others). This is because it insulates better at those lower temperatures.
I personally used mineral wool board too on my oven (and would have preferred blanket as well).
I would recommend a layer of ceramic blanket between the brick and this mineral wool for those that need that extra sense of security and peace of mind and do not mind the extra expense for the blanket.
However, I feel that it is not always required because the heat that is conducted through the brick (or leaked out through any cracks) in our wood-fired ovens is not high enough to have a negative impact on the mineral wool.
A plus in tayloring the insulation (or insulating layers) is that less heat is conducted away from the hot face material which results in more heat staying in the brick. This can result in less fuel consumption and longer heat retention.

Last edited by altamont; 12-22-2010 at 07:20 AM.
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  #17  
Old 12-22-2010, 04:39 PM
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Default Re: Rock wool as insulator?

Altamont,

Are you recommending tailoring mineral wool board (ie: a geodesic shell) around the dome with ceramic blanket in between?
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Old 12-22-2010, 04:55 PM
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Default Re: Rock wool as insulator?

I am not strongly recommending using mineral wool board - it is much harder to work will as it just does not bend. If only the blanket form of mineral wool was easy to find...

My thought was that one layer of ceramic blanket between would give some people some peace of mind. It is used as a hot-face lining in many industrial furnace designs so it can very easily withstand the much cooler temperatures between the firebrick and mineral wool. It would partially fill some of the void between the curved brick surface and the flat surface of the mineral wool board and not slide down from gravity (in the more vertical areas of the dome).
I still have to come up with the chimney on my oven and a weather-proof house for the dome. Much to my chagrin, I can only fire up in good weather - everything is now covered up under an ugly blue tarp to keep the mineral wool dry :-(
I can say that I have fired the oven up to clear, maintained a small fire on the side and fired pizzas on the first evening. I put 2" thick cal-sil board up as a door. Open those up two days (evenings) later and I am still over 350 F. on the sidewalls and top of the dome (inside of course). Ambient temps the last time I did that and took measurements were @ 70 - 75 F. peak during the afternoon and down to @ 47 - 52 F. at night. Just the one layer of 2" mineral wool board covered by the tarp (only when not firing).
I plan on keeping that mineral wool in place and using up the remainder of the box about the top. Then back fill between the outside walls when built and the mineral wool with bulk fiberglass insulation.

Getting back to you question, if someone had the patience to cut the mineral wool (and taper the joints for tighter fit) - well that would be great. Any openings between pieces of mineral wool are basically uninsulated voids. If blanket were under the mineral wool, there would be some insulation instead of none.

Last edited by altamont; 12-22-2010 at 04:57 PM.
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  #19  
Old 12-22-2010, 07:29 PM
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Default Re: Rock wool as insulator?

John, I found that the board wasn't what I was expecting with regard to flexability, but I was able to get the board around the oven. I think you can find thinner boards than what I used and you might be able to split the boards. If you're enclosing your oven then the boards work just fine and the're available at a good cost. I don't think that unless you had a very large crack that vents flame through the dome rather than out the flue, that Mineral Wool have any problem. For a stucco covered dome you might have real problems getting the insulation in a dome shape ready to stucco. If you need a local source send me an E.

Chris.
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  #20  
Old 12-22-2010, 11:27 PM
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Default Re: Rock wool as insulator?

Thanks, Chris. My original plans were to use ceramic blanket and vermicrete followed by loose vermiculite housed in a cement board enclosure like yours. However, if I was able to source a case of insblock 19 like I did for my oven floor insulation ($75 for 8 3'x1'x2" boards), I might think about it. Although Dmun recommends just using more ceramic blanket, I like the idea that ceramic blanket is best used in direct contact with a 'hot face' and Insblock is best used as a backup insulation layer in kilns. I would separate the 2" thick 2-ply boards into 1" boards, and maybe have enough to cover my dome. I'll have to do the math first.
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