Questions, Questions, Questions

[Dan94550]

Re: Questions, Questions, Questions

That plan to thickly cover the outside of the joints with mortar rather than put a thin mortar layer in the joint seems odd to me. I am certainly no mason, but why not just use refractory mortar in the joint? It should be much stronger than covering the outside of the joint, and will probably use less mortar. Your walls are quite thick, so I agree, no cladding. You'll be glad you are using the insulating blanket. It will be much easier to work with than loose fill around the walls.

I am not a mason either. This is why I am throwing these questions out there and I'm getting more and more confused as there are different techniques. All I know is that I will use the blanket and still use the loose vermiculite to fill in any voids.

Maybe I'll start a new thread with a poll if I can't get an answer that I'm satisfied with.

Pros or cons on either method would be greatly appreciated.

[jwnorris]

Re: Questions, Questions, Questions

Seal your oven in two steps. First, using refractory mortar, seal each joint the oven dome; between the oven dome and the insulating hearth; between the oven dome and oven vent; and between the decorative arch and the oven chamber.

Moisten each joint using a sponge, then seal the oven joints by applying a 2"H x 4"W strip of refractory mortar cross the outside of the seam. Do not put mortar inside the joint as thermal expansion could cause the oven to crack. Seal the oven dome to the insulating hearth with a 2"W x 4"H strip of refractory mortar, the seal the oven dome to the vent and arch.

I took the above from the FB Casa installation manual. This is a seal and is not meant to connect the two dome [for lack of a better term] pieces together. It is for thermal expansion.

Dan, i think that you re-cap is going to work fine.

J W

[maver]

Re: Questions, Questions, Questions

That plan to thickly cover the outside of the joints with mortar rather than put a thin mortar layer in the joint seems odd to me. I am certainly no mason, but why not just use refractory mortar in the joint? It should be much stronger than covering the outside of the joint, and will probably use less mortar. Your walls are quite thick, so I agree, no cladding. You'll be glad you are using the insulating blanket. It will be much easier to work with than loose fill around the walls.

[Dan94550]

Re: Questions, Questions, Questions

Being that the outside of the oven is rectangular in shape and not domed, I am still a little confused on how to assemble. Here is what I get from what I am reading, do not mortar the joints but cover the joints with 1" X 2"-3" refractory motar, cover with insulating (refractory) blanket, frame in, and back-fill voids with loose vermiculite. The walls are 4" - 6" thick so I don't think I will coat the entire oven with the mortar.

I will now order another bag of refrax mortar and the insulating blanket from FB.

[jwnorris]

Re: Questions, Questions, Questions

Looking at this from the point of view of a FB modular oven, here is what I would do.

1. Mortar between the floor pieces. As long as your base structure is level, setting the floor in mortar is optional.
2. As for the gaps in the bottom of the floor pieces, you could fill them with refractory mortar to give then somewhat of an equal mass - the difference in thickness may lead to uneven floor temperatures.
3. Do not mortar between the dome and the floor. It should just set on the floor.
4. Do not mortar between dome pieces.
5. When dome is complete, cover the joints in the dome [including the joint where the dome sits on the floor] with refractory mortar - about 1" thick and about 2" to 3" wide.

From this point, if extra heat storage mass is desired, cover the entire dome with 1" to 2" of refractory mortar. Then insulate. I would use at least a 1" thick refractory blanket [such as the one that FB sells]. Maybe use two layers of blanket.

Then, after framing the enclosure, fill any space left with loose vermiculite - including the top of the dome.

Good luck.

J W

[maver]

Re: Questions, Questions, Questions

With that narrow a space for insulation you should seriously consider using a ceramic blanket from either a local refractory supplier or from FB.com. You could add extra vermiculite if you have room above the oven to ensure good heat retention.

You also should not rely on vermiculite to seal the oven but I don't know that it really needs sealing with your design. If you are sure it will not be moved then I think I'd use a refractory mortar.

[Dan94550]

Re: Questions, Questions, Questions

right, sorry, I forgot your original thread and was just reviewing it. How much room for insulation have you allowed? I do think you'll want to mortar your joints, although considering it looks like it is self supporting I wonder if you could just 'seal' it with a fireclay paste instead? Only benefit would be ability to disassemble it if you ever need to.

I'm allowing 4" on the sides and probably the same on top. I am limited on the sides but could go more on top. I don't plan on disassemling it so I could seal it or would the vermiculite be enough?

Both of my brother-in-laws looked at my father-in-laws indoor built in and my wife took pictures but it is hard to tell if it had mortar or not. I really do want to finish it but I don't want to screw it up.

[maver]

Re: Questions, Questions, Questions

right, sorry, I forgot your original thread and was just reviewing it. How much room for insulation have you allowed? I do think you'll want to mortar your joints, although considering it looks like it is self supporting I wonder if you could just 'seal' it with a fireclay paste instead? Only benefit would be ability to disassemble it if you ever need to.

[Dan94550]

Re: Questions, Questions, Questions

Dan, what are you showing there? The blocks look like a refractory material (just based on color and texture). You have a dome that will fit inside that (or a barrel on top)? The proportions of your blocks look like they are appropriate for a barrel oven. It looks like it all sits on a layer of vermiculite concrete. Is that a FornoBravo product? Interesting.

Marc

Marc,

See my original post in the "Newbie" section and you can see what I have. There are pictures of it upside down in my yard and a picture in a brochure.

Dan

[maver]

Re: Questions, Questions, Questions

Dan, what are you showing there? The blocks look like a refractory material (just based on color and texture). You have a dome that will fit inside that (or a barrel on top)? The proportions of your blocks look like they are appropriate for a barrel oven. It looks like it all sits on a layer of vermiculite concrete. Is that a FornoBravo product? Interesting.

Marc

[Dan94550]

Re: Questions, Questions, Questions

Neill, dmun,

Thanks for the reponses. I went ahead and mortared in the oven base and took a couple of pictures with the 2nd layer just dry fitted. There is a little bit of a gap so I don't know if it will be worth adding mortar. Since the oven is square on the outside (dome inside), I plan on building a metal stud frame with hardi backer sides and back filling with vermiculite. I thought that I read on another thread that vermiculite alone is a better insulator that the mix. Is that true? Any comments welcomed.

Thanks again
Dan

[dmun]

Re: Questions, Questions, Questions

A couple of notes. I, like Neill, don't know about the FB prefab ovens but i distinctly remember that the floor sectors are put together with refractory mortar.

The difference between using loose vermiculite and the vermiculite concrete, is that the latter stays put - it doesn't leak out of any small crack in your enclosure. One ten buck bag of portland glues together a whole lot of vermiculite. My oven was in in enclosure, and I put all my vermiculite in concrete.

I know that pre-fab ovens are more robust than pompeiis, but I think a bunch of the cracking problems are from thermal shock, and I think this is much reduced if you don't fire your oven until it's insulated, FWIW.

[nissanneill]

Re: Questions, Questions, Questions

Hi Dan,
sounds like you are talkig to deaf ears.
From reading your post, it sounds like you are assembling a prefabricated oven - yes?
I have completed a brick Pompeii which is different in regards to firebrick heart and dome rather than moulded/pressed refractory mortar.
If you are using the high temp adhesive for your dome, I would cement your floor panels but only if the they not fit nice and flush together. Small gaps will quickly fill with ash but if the gaps are larger, then I would cement them.
I would most certainly cement the dome sections together using the recommended high temperature adhesive, but follow the manufacturer's recomendations as they have the best experiences for all to follow.
As far as the outer insulation is concerned, if you are building a frame/enclosure to contain loose vermiculite (or similar), or you are requiring to mix a 5:1 ratio of vermiculite cement and render the dome, either is quite appropriate but depends on your personal preferences. I prefered the hemispherical dome appearence rather than a small building constructed, so I plastered the brick dome over a 1" thick superwool cover with 3 X 1" layers of vermiculite cement. See:

https://www.fornobravo.com/forum/f21/neill-s-pompeii-4-a-2045.html

I would start with the small drying fires as soon as possible, in fact I started when my dome was closed and whilst I was insulating the dome.
Hope this is helpful to you and good luck!

Regards.

Neill

[Dan94550]

I didn't get any responses on the newbie thread so I'll try this one since there are a few more viewing.

Well I got side-tracked for a few weeks by starting the framing to my outdoor kitchen which I attached to the oven hearth. I plan on setting the oven floor tonight when I get home from work and I decided not to fill the cavities but since the floor is in 3 pieces, do I put mortar in between the joints or just dry fit them?

After letting the base set, should the rest of the pieces be dry fitted also or should the be mortared? Once the oven is in place can I begin with some fires or should I wait till the framing with metal studs is complete and back filled with vermiculite? One last question, should the vermiculite be dry or 5-1mixture as in the hearth?

Sorry for all the questions at one time but since I've been working on the kitchen, I got sidetracked but I've been thinking about all these things and need to get-er-done.

Cheers,
Dan