36'' brick oven in northern Sweden

[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]

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.

[johanr]

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

[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

[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.

[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.

[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]

Russell (UtahBeehiver) used a similar template, but a little more as a guide. He used a larger curved trowell to actually place the vcrete. And if ya'll haven't seen it go check out his copper clad oven. Here is his photo album. He has also added some finished pics of his oven and stand that were never posted over here. It is well worth the visit .

[Gulf]

.......... I'm planning for to cover the oven in 6'' vermicrete aiming for a perfectly round finish. Any good tips on how to acchieve that easily? I thought to just mix the vermicrete a little stiff and then lay thick (6'') loaves of vermicrete starting from the bottom and go around the dome, working in circles and using a large square trowel to shape it. Is that a good idea, or should I do it differently? Using some sort of form/grid/net? Any suggestions appreciated!

First off, I think that it would be to your advantage to have a blanket between the vcrete and the dome. Aside from the insulation factor, I feel that it acts as an expansion joint. Even if it is only a 1" layer. That out of the way, I used a rotating template to get as close to a perfect sphere as I could. On my template, I attached a homemade curve trowel to the arm. It was attached by drywall screws that allowed me to easily remove and raise it up with each pass.

[david s]

I finished the brick laying today by laying the last bits of the chimney base. It felt really good! I will have a round metal chimney manufactured including base and cap, either in stainless or copper. I drilled some holes in the top chimeny bricks (before laying them) to later attach such a chimney base. Which gives rise to the question: how high should the chimney be? According to the FB plan, I should be fine with a 6'' (15 cm) chimney. I prefer not to have it too tall due to esthetics. Perhaps it is better to go for a lower 8'' chimney instead?

In parallell, I'm planning for to cover the oven in 6'' vermicrete aiming for a perfectly round finish. Any good tips on how to acchieve that easily? I thought to just mix the vermicrete a little stiff and then lay thick (6'') loaves of vermicrete starting from the bottom and go around the dome, working in circles and using a large square trowel to shape it. Is that a good idea, or should I do it differently? Using some sort of form/grid/net? Any suggestions appreciated!

Getting rid of the excess water in the vermicrete is difficult, especially if the layer is thick. It's like a pile of sand that will remain wet for months under the surface. I've found the best way to make a thick layer of vermicrete is to do it in layers of about an inch and a half with a week of sun and wind between each layer, weather permitting, and cover it if it looks like rain. Also found the best ratio is 10:3:1, by volume of vermiculite, water, cement and for every 10 litres (two gallons) of vermiculite add a handful of powdered clay. Vermiculte will vary depending where or who makes it so you may need to adjust the water proportion a little. The finer the grade the more water is required. Also I now use 50/50 vermiculite and perlite which makes a better mix than either of them used alone. If you use more cement then you reduce the insulation value,(see attached doc), less than 10:1 is very difficult to apply vertically.

[johanr]

I finished the brick laying today by laying the last bits of the chimney base. It felt really good! I will have a round metal chimney manufactured including base and cap, either in stainless or copper. I drilled some holes in the top chimeny bricks (before laying them) to later attach such a chimney base. Which gives rise to the question: how high should the chimney be? According to the FB plan, I should be fine with a 6'' (15 cm) chimney. I prefer not to have it too tall due to esthetics. Perhaps it is better to go for a lower 8'' chimney instead?

In parallell, I'm planning for to cover the oven in 6'' vermicrete aiming for a perfectly round finish. Any good tips on how to acchieve that easily? I thought to just mix the vermicrete a little stiff and then lay thick (6'') loaves of vermicrete starting from the bottom and go around the dome, working in circles and using a large square trowel to shape it. Is that a good idea, or should I do it differently? Using some sort of form/grid/net? Any suggestions appreciated!

[david s]

Also, I skipped water curing the vcrete as I found no info on anyone doing that.

There is no need to cure the vermicrete because it contains so much extra water that will act to cure it without the need to cover it.

[johanr]

Also, I skipped water curing the vcrete as I found no info on anyone doing that.

[johanr]

Thanks for that info, I started the build 4 days after pouring the vcrete. At that time it was still a bit like cork. Now a week later it feels rock solid.
I decided to include a heat break by leaving 3 mm gap in floor and beteende arches. I will fill that later with ceramic paper 2-3 mm thick (ebay UK) and fill the gap with home brew althouh with extra fine sand (0-2mm). Although, the gap in the floor will be left open and later filled with ash.
Right now, I have finished the sides for the vent arch and will wait 1-2 days before building the arch and chimney.

[david s]

I missed your question about how long to wait before building over the vermicrete layer. the answer is that it will still be wet and will take months to dry out completely. You can use the oven but you will find that its performance will keep on improving as the water is slowly driven out. It will just take a long time. See attached experiment.