36'' brick oven in northern Sweden

[johanr]

Good suggestions! I have however not been able to buy any ceramic fiber blanket (that did not cost a fortune). However, I can buy standard Rockwool (/mineral wool) blanket 1'' thick that is sandwiched between two metal nets, like the one you put on your ceramic blanket to hold it down. Do you think that could be good enough?

[Gulf]

Here is a discussion on Mineral Wool/RockWool that you may find interesting. I haven't used it, but it seems that it is a good option to ceramic fiber blanket. You mentioned 6" of vcrete. I think that I would go with 3" of mineral wool and 3" vcrete to bring it back to shape. I don't know how much the wire mesh on the roll will help or hurt, though. I'm wondering if can be removed so that you don't have it between the layers. Or, if it is possible for you to get it without the mesh? Maybe, someone who has actually used it in an oven application will weigh in on this thread.

I hope this helps.

[david s]

I used Rockpool blanket (no mesh) on a couple of builds. It is slightly less effective as an insulator compared to ceramic blanket, but is cheaper. What I don't like about it is that it is far more water absorbant than ceramic blanket and also it does not cut as well. I agree with Gulf that a layer of blanket acts well as an expansion layer, reducing problems with the vermicrete layer.

[johanr]

Thanks! The local stores carries rockwool blankets with wire mesh and aluminium/woven foil/fabric on one side. That side of the blanket is specified for 300 C (570 F) so that should go out, and the other side that would be against the dome is specified for 1000 C (1800 F). The water absorption is specified

[johanr]

Weird, half of my post disappeared..
Well. Water absorption

[johanr]

And again..! Perhaps water absorption is a sensitive issue..
<1% so that's not much, but I guess more that modern ceramic fibers. Rockwool blankets available were 3.6 m2 per roll so that would be enough for one layer, but perhaps it would be easier and better to do two layers and reduce vermicrete applied for shaping the dome.

[Gulf]

Thanks! The local stores carries rockwool blankets with wire mesh and aluminium/woven foil/fabric on one side. That side of the blanket is specified for 300 C (570 F) so that should go out, and the other side that would be against the dome is specified for 1000 C (1800 F). The water absorption is specified

And again..! Perhaps water absorption is a sensitive issue..
<1% so that's not much, but I guess more that modern ceramic fibers. Rockwool blankets available were 3.6 m2 per roll so that would be enough for one layer, but perhaps it would be easier and better to do two layers and reduce vermicrete applied for shaping the dome.

"Aluminum/woven foil/fabric" That sounds like it may have a porous backing that would allow it to breath. If it is solid, I would try to find blanket without the foil or remove it. It is believed the foil will trap moisture. Some, that have used the foil backed blanket, went back and poked a "gazillion" holes in it to get around this. Also, If you can go 3 layers of blanket that would reduce the amount of vermicrete that will need to dry even more. Although, it does add some bonus insulation, I consider the vermicrete as a shaping layer and firm base to add some type of render..

[johanr]

The woven fabric on the RockWool Vent felt like it would easily let moist through. I believe there is also an aluminum-foil version of this blanket, that perhaps is not as suitable then. One issue I found was a little tricky was how to keep the blanket tightly fit round the dome. I made some cuts in the square blanket to make it better fit the round dome, by overlappning the cuts. Are there any clever tricks here to get the blanket into good shaping prior to vermicrete? I've seen some people put wire mesh on the blanket, but not shure how to secure that to shape. Perhaps just get it into acceptable shape and then when vermicrete is put on, it helps weigh it down and secure it?
The Rockwool blanket was good priced at around 50$. I would say that perhaps even cheaper than for me to use the vermiculite, and another reason to go for 2-3 passes of RockWool blanket. If I can just return some of the 400 liters of vermiculite : )

[Gulf]

Take a look at this Forno Bravo video.

[cobblerdave]

G'day
I used rockwool as a Secondary insulation. 4 ins of rockwool OVER 2 ins of ceramic blanket.
Wire mesh over that and rendered over the wire.
I checked a no of years later and posted the results but cant find that thread now. Yes I cut a hole in the dome render.
My recommends would be a 3 in layer of V-crete to take the high heat then the rockwool. (Sorry Gulf)
As for the aluminium. All ovens other than those under full cover get damp from time to time. Its never a real problem you just need to fire the oven a few times. Aluminium out of the open air in contact with moisture will corrode. Just get a piece of cooking foil and put it under brick and leave in the yard on the ground. It will start to corrode before the weeks out.
Regards dave

[Gulf]

G'day
I used rockwool as a Secondary insulation. 4 ins of rockwool OVER 2 ins of ceramic blanket.
Wire mesh over that and rendered over the wire.
I checked a no of years later and posted the results but cant find that thread now. Yes I cut a hole in the dome render.
My recommends would be a 3 in layer of V-crete to take the high heat then the rockwool. (Sorry Gulf)
As for the aluminium. All ovens other than those under full cover get damp from time to time. Its never a real problem you just need to fire the oven a few times. Aluminium out of the open air in contact with moisture will corrode. Just get a piece of cooking foil and put it under brick and leave in the yard on the ground. It will start to corrode before the weeks out.
Regards dave

No worries, old friend.

In my first reply I acknowledged that I had no experience with mineral wool in this type of application. I had hoped that folks with first hand experience with it would weigh in. I knew that it wasn't sufficient for a kiln. Even though, many think that it is an alternative for the temps of a WFO. However, I am real curious why 2" of ceramic fiber blanket wont stop "true" mineral wool form melting but, 3" of vermiculite will?

just askin'

[johanr]

Thanks for all input!
But really, what temperature should I expect at the outside of the dome bricks? If Rockwool is specified to withstand 1000 C (1800 F) before melting, should that not be enough? I would have guessed the dome outside to be perhaps maximum 600 C, but I have of course no real idea.

[david s]

you won't get anywhere near 600 C on the outside of the bricks. 500 at tops.

[johanr]

Which would make me think rockwool should be fine directly on dome. Adding vermicrete below and outside the rockwool would add to more work.

[david s]

The ovens that I used Rockpool insulation on had it directly over the dome, then a layer of vermicrete over the Rockpool. They work fine although I've not pulled them apart to inspect the Rockpool. The vermicrete was a little more difficult to apply over the Rockpool compared to ceramic blanket. It was more difficult when asking the vermicrete to stick and stand up against the Rockpool. I had to come back and patch a few areas the next day from memory.