#11  
Old 04-19-2008, 09:41 AM
gjbingham's Avatar
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Default Re: Is ceramic fiber insulating board worth it?

That's wierd Jim. Mine stays cold to the touch underneath the hearth until probably 5 -6 hours after firing the oven. 12 hours later, its around 100 - 110 degrees F. That's with 4 inches over vermicrete under the floor of the oven. I still have trouble maintaining a really hot floor for any length of time without having a pretty hot fire burning on the side. That's why I would recommend 6 inches of vermicrete for the insulation hearth vs. 4. I'd still recommend 3 inches of Isoboard first though.
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  #12  
Old 04-29-2008, 08:15 AM
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Default Re: Is ceramic fiber insulating board worth it?

I went for the boards. When I calculated the time of pouring the vermiculite-cement, added the number of costly ways I could botch the job and compared it all with just unwrapping the boards and putting them on top of the supporting board/slab there was no comparison ... The proper boards are quite pricey in the UK, but I still think they make a lot of sense.

W.
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  #13  
Old 05-01-2008, 08:19 AM
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Default Re: Is ceramic fiber insulating board worth it?

I ordered the FB boards and they will be used.

Is it overkill to place the vermiculite concrete under the boards? I know you can never have too much insulation, but is it worth the trouble?

What will the temperature get up to under the FB boards? Does anyone think that it could get as high as 200 degrees?

What are some alternatives that others have tried under the FB boards to further insulate them from the concrete slab? alternatives other than vermiculite concrete?

to get to a 41.5" cooking surface, I only have 2.5 inches to use for extra insulation like the vermiculite.

has anyone used asbestos insulation under the FB boards?
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  #14  
Old 05-01-2008, 08:53 AM
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Default Re: Is ceramic fiber insulating board worth it?

Quote:
Originally Posted by maburton View Post
I ordered the FB boards and they will be used.
Same here!

Quote:
Originally Posted by maburton View Post
What will the temperature get up to under the FB boards? Does anyone think that it could get as high as 200 degrees?
A quick calculation (steady state) assuming 5cm (2") of oven floor refractory (1.31 W/(m K) - like brick) and 5cm of FB (0.1 W/(m K) - slightly pessimistic), internal oven temperature 400C (673K), heat transfer coefficient of 20 W/ (m2 K) (standard for brick to air - assuming that FB is exchanging heat with the ambient air or sat on a thin cement board and the ambient temperature is 17C - what we have right now) the temperature of outer surface of FB is 323K (50C)

Quote:
Originally Posted by maburton View Post
has anyone used asbestos insulation under the FB boards?
I wouldn't. Not healthy, not even legal in many places.

Yours geekily,

W.
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Old 05-01-2008, 06:07 PM
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Default Re: Is ceramic fiber insulating board worth it?

Quote:
Originally Posted by Wlodek View Post
A quick calculation (steady state) assuming 5cm (2") of oven floor refractory (1.31 W/(m K) - like brick) and 5cm of FB (0.1 W/(m K) - slightly pessimistic), internal oven temperature 400C (673K), heat transfer coefficient of 20 W/ (m2 K) (standard for brick to air - assuming that FB is exchanging heat with the ambient air or sat on a thin cement board and the ambient temperature is 17C - what we have right now) the temperature of outer surface of FB is 323K (50C)
That's so fantastically geeky... I love it! The scary part is that it makes sense.

Last edited by Ed_; 05-01-2008 at 06:08 PM. Reason: Hey look, I'm a laborer!
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  #16  
Old 05-02-2008, 02:33 AM
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Default Re: Is ceramic fiber insulating board worth it?

Quote:
Originally Posted by Ed_ View Post
The scary part is that it makes sense.
Thanks Ed, I must say I was suprised myself ...
W.
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  #17  
Old 05-02-2008, 08:04 AM
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Default Re: Is ceramic fiber insulating board worth it?

Now, following this result I have probably very nearly done something stupid. Perhaps someone here will correct me (or confirm I am right) before I carry it out .

I thought that 50C is quite hot for outside of the oven and will make the oven lose lots of energy. The model above actually describes my set-up well: 2in of oven floor resting on 2in of FB.

So I bought some inexpensive high density fiberglass slabs to put under the FB.
The slabs are fibreglassy, designed to go into cavity walls or under flooring, quite dense, about 2in thick and would surely bring the 50C down to not much at all. And they would not be exposed to high temperatures, as these will be taken off by the FB. That was my rationale.

...... but then came The Doubts.

Because while FB is tried and tested by this Forum, the fibreglass slab possibly isn't.

On the specs for the fibreglass slab a sub-flooring application is included (under concrete screed), so I hope that it will remain stable under the relatively small pressure from the oven, spread over the approx. 2sq.m. of oven support area.

Or will it all wobble ???

.... or even sink ?

Any experience, advice , voice of reason (on this sunny Friday afternoon)?

Yours,
W.
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  #18  
Old 05-02-2008, 05:50 PM
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Default Re: Is ceramic fiber insulating board worth it?

I have started building a pompeii oven and I am worried about ceramic fibers. I've read much information about building ovens of this kind on fornobravo. Because I live in the Netherlands I also read information more close where I live. And there is a firebrick seller that doesn't sell ceramic fiber blanquets anymore.
He says: (the next is dutch)
Het keramisch vezeldeken wordt NIET meer geleverd. Dit i.v.m. de wereldwijde discussie over de mogelijke gevaren voor de gezondheid. Als uitstekend alternatief wordt de Superwool 607 geleverd.
Here is my translation: Because of the worldwide discussion about the possible hazards with respect to human health, we don't sell the ceramic fiber blanquet anymore. I like to sell my Superwool 607

If this is true, we have to get alternatives.
Is it, or is it just a way to get the Superwool 607 selled?

kind regards, Henk
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  #19  
Old 05-02-2008, 09:35 PM
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Default Re: Is ceramic fiber insulating board worth it?

Sounds like he has Superwool 607 to sell and not ceramic blankets. Business is business. Certainly, not advisable to breath the ceramic fibers. I know of no other problems with the stuff. Once incased inside the layers of the oven, I think it will be fine.
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  #20  
Old 05-03-2008, 04:31 AM
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Default Re: Is ceramic fiber insulating board worth it?

You don't want to breathe any of this stuff, even the brick and concrete dust. Just because it's asbestos-free doesn't mean you don't want this dust in your lungs. Silly paper dust masks are not enough, get a low end respirator that lets you breath out un-obstructed, and filters the air on the way in:



This will make your life easier.

Maybe it's time to bump up the safety thread with all the new builders coming in in the spring.
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