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Post by navylark on Aug 1, 2012 21:31:09 GMT
Hi all
I am new to the forum and currently building the base for a pompeii oven. As with most jobs I do they evolve as I am going a long, buying and acquiring items as I go. One thought I had following a trawl through various websites was for cheaper alternatives to insulation of the dome. Has anyone used Rockwool insulation squashed down and sealed in with chicken wire and cemented/rendered over? It is far cheaper than proprietary fire blanket, non flammable and cheap to get. I happen to have access to it for free - even better. Look forward to your thoughts to assist my evolutionary oven.
Cheers Nick
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Post by cannyfradock on Aug 1, 2012 22:08:48 GMT
Hello Nick......welcome to the forum. As these ovens can easily reach +500C, normal rockwool hasn't got enough fire-proofing to be used safely. Chicken wire etc is usually used to hold the blanket in place, but it shouldn't be compresssed. The fire-blanket from Liam.. http://www.kilnlinings.co.uk./ is competitively priced....and so are his fire-bricks etc. If you are getting your bricks from somewhere else or using storage heater bricks.....or even clay bricks, then "Sheffield insulation" (they've got outlets all over the UK) sell a suitable product for about £45? We also have a discount account with Jewsons which may save you a few bob.. ukwoodfiredovenforum.proboards.com/index.cgi?board=membersdiscounts&action=display&thread=82 Doing a lot of research of old Pompeii builds may also help you out in saving money or help you with your build. As well as the Pompeii builds on this forum there is also a wealth of info on our old forum.. woodovenukforum.forumup.co.uk/viewforum.php?f=49&mforum=woodovenukforum (you need to register to see all the pictures and links) Terry
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Post by bookemdanno on Aug 1, 2012 22:35:30 GMT
Not wanting to poo-poo Terrys' comments, as he is a goldmine of experience, but...
Rockwool Website states..."Rockwool stone wool insulation is classified as A1 which is the highest ranking of the reaction to fire classifications. Non-combustible in nature, Rockwool can withstand temperatures in excess of 1000°C without melting."
Can't find where i saw it but i think Rockwool has a higher insulation value than Ceramic Blanket also.
Now, i'm not saying that its better. Its not proven.
It will take some people to take a chance and use it, then report their findings over time. I will be one, as i'm using the Rockwool Fire Barrier, but i do have some ceramic blanket also, which will probably go on first. But i doubt we will ever be able to do back to back tests. Make sure that it is in fact Rockwool Mineral Wool, and check the Tech Specs of the particular insulation you intend to use. Some mineral wool insulation has additives, and can be made of lesser materials which may not tolerate the extreme environment these WFOs can create.
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Post by cannyfradock on Aug 2, 2012 7:47:06 GMT
Bookemdanno
Never be afraid to contradict or give differing opinions on my comments. I'm still learning and try to advise the best I can, but without yourself and the other members and Moderators contributions, this forum wouldn't be able to be as popular as it is.
Your input is always truly appreciated.
Terry
p.s.....Interesting info on the Rockwool
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Post by faz on Aug 2, 2012 7:50:25 GMT
It would be possible to apply a thin (say 1 inch thick) layer of vermicrete on the dome underneath the rockwool. This would reduce the maximum temperature the rockwool would be exposed to and it could then still be covered with a further layer of vermicrete over the top for additional insulation.
There is no insulation reason why it has to be blanket first, then vermicrete, although it would be easier to apply the vermicrete in a single layer rather than splitting it into two. As long as there is a blanket there it will allow movement/expansion of the dome without directly cracking the external render.
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Post by cannyfradock on Aug 2, 2012 9:37:44 GMT
OK....This is a subject that has been discussed for many years by us and also on the FB forum. Have searched through our ...and FB forums on this subject trying to find the answer. It seems that 80% of people say it's OK....with 20% of people saying...use only the correct thermal blanket .......so decided to contact Technical support at www.rockwool.co.uk/ I have been advised that although their normal rockwool.... which can withstand heat of 1000C...will only withstand this heat once. Rockwool contain a % of binders which when coming into contact with direct heat of 230C will start to dissintegrate, which in turn will turn the rockwool back to dust. The only product they make which is suitable for our needs is a product called "Industrial wired mat" which has chicken wire attached on one side and can take repeated heat of up to 600C. Terry Have just received an e-mail from Rockwool stating that their Rockwool fire-barrier also has the same properties as the Industrial wired mat...
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Post by bookemdanno on Aug 2, 2012 20:29:46 GMT
Thanks Terry, that's the way Boy! Good work! That's set my mind to rest too about the Fire Barrier. Awesome place this!
The Vermicrete layer first was something i'd pondered too. Will look into that one.
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Post by navylark on Aug 2, 2012 21:59:08 GMT
Thanks for the info, the internet and this forum is truly shared knowledge and experience.
I will read the tech spec of the stuff that I have at my disposal.
Cheers Nick
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Post by turkey on Aug 3, 2012 10:56:00 GMT
the vermicrete will not be any better than the rockwoll fire barrier as it is cement based and as such starts to deteriorate at 600C
that is on the outside of the brick, so the internal face of the brick will get hotter than this, I am unsure what the external insulation facing part will reach in normal operation, I suspect these products will be fine for the limited use residential ovens and suspect the insulation side will hardly get over 600C if at all.
perhaps scouring some posts on FB where folks have uploaded their thermocouple logs might give better insight to the temps the insulation actually faces.
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Post by faz on Aug 3, 2012 13:37:35 GMT
If the outside of the brick wil exceed 600C, which I guess is feasible occasionally on a well soaked & hard fired oven, this could cause the binder holding the very inside layer of vermicrete to break down. So the question is, will slight deterioration of this non structural element of the oven make any difference? Even if the inner face of the vermicrete loosens slightly, you'll still retain the insulation properties, and the final vermicrete layer/render will ensure the exterior of the oven has the required structural strength to remain watertight etc.
I agree that actual logs of temperature would help settle this.
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Post by turkey on Aug 3, 2012 14:43:33 GMT
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Post by cannyfradock on Aug 3, 2012 15:37:39 GMT
This thread is churning up some interesting stuff....cheers Nick.
After my first build (a guesstimate) I have followed other forums methods...and then the advice from our forums. The more you build these beauties the more you think ...is there a better way than....dome, thermal blanket, vermecrete then waterproof render (I hate using vermicrete)......but.....and it's a big but.....after reading the posts on this thread, it does make sense to follow the T & T method that is used on a normal domestic construction.
Terry
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Post by jerrym on Aug 4, 2012 8:49:00 GMT
i used rockwool on my old "clay" brick barrel oven initially. it was under the hearth insulation (thermal block). i also had it on the roof.
i saw no degradation.
i've taken it off the roof as i could not keep it dry. i also ended up taking it out of the hearth whilst trying out various hearth setups (now using sand).
i would use rockwool again. the itchy aspect being the only downside.
what's it's service temp is will be debatable - i had 750C in mind when i selected it.
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Post by bigdavenorcott on Jun 9, 2014 9:23:06 GMT
OK....This is a subject that has been discussed for many years by us and also on the FB forum. Have searched through our ...and FB forums on this subject trying to find the answer. It seems that 80% of people say it's OK....with 20% of people saying...use only the correct thermal blanket .......so decided to contact Technical support at www.rockwool.co.uk/ I have been advised that although their normal rockwool.... which can withstand heat of 1000C...will only withstand this heat once. Rockwool contain a % of binders which when coming into contact with direct heat of 230C will start to dissintegrate, which in turn will turn the rockwool back to dust. The only product they make which is suitable for our needs is a product called "Industrial wired mat" which has chicken wire attached on one side and can take repeated heat of up to 600C. Terry Have just received an e-mail from Rockwool stating that their Rockwool fire-barrier also has the same properties as the Industrial wired mat... Hi all Great info - I'm also hoping to use Rockwool to avoid the health aspects of using CF, and as a lesser aim to reduce costs. My main concern with the CF is that I don't know if it'll be me that ends up demolishing the oven - I don't want to expose someone in the future to risks breathing in the fibres when they smash my eyesore up with a sledgehammer Trying to figure out what to use - the Rockwool fire barrier seemed like a winner, but on their data page it seems to say that it only maintains its integrity for up to 4 hours before disintegrating: www.rockwool.co.uk/products/u/2011.product/9842/building-insulation/fire-barrier-systems-Danno - can I ask if your rockwool has stood up to the repeated heat OK? Cheers!
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Post by bigdavenorcott on Jun 9, 2014 10:21:40 GMT
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