Mortar for outdoor bake oven?

[johanras]

It depends a bit on how long it's been since the last burning, but up to 2 hours, usually 1.5, to get it thoroughly warm.

 

[Serjon1]

Hi Johan!
Like so many others, I am impressed by the beautiful stone oven you built. Now I am eager to embark on my own project. Firebricks have been purchased along with a smoke pipe, and the hole for the foundation is dug. Now I'll cast to then build the foundation with lecablock. However, I'm unsure if 19 cm in width is sufficient? What dimensions did you choose? If it's not too much to ask, could you also advise on anything else I should consider beyond what is available in the posts? Would you have done anything differently today?
All the best!

 

[Dan_Johansson]

Hi Johan!
I, like so many others, have been impressed by the fine stone oven you built. Now I'm eager to get started myself. Firebrick has been purchased as well as smoke pipes, and the hole for the foundation has been dug. Now I'm going to cast and then build up the foundation with lecablock. However, I'm unsure if 19 cm in width is sufficient? What dimensions did you choose? If it's not too much to ask, could you also advise if there's anything else I should consider beyond what can be read in the feed? Would you have done anything differently today?
All the best!

19 cm wide lecablocks are more than sufficient, if you build a U and cast a concrete slab on top....
I would recommend you get an account on Forno Bravo, if you are proficient in English, there is lots of information there...

 

[Serjon1]

19 cm wide lecablock is more than sufficient if you build a U and pour a concrete slab on top...
I can recommend getting an account on Forno Bravo, if you are proficient in English, as there's a wealth of information there...

Thank you! I'll go with 19 cm. I've also visited Forno Bravo, lots to learn and be inspired by.
All the best!

 

[Dan_Johansson]

Thanks! Then I'll go with 19cm. I've also been on Forno Bravo, lots to learn and get inspired by.
All the best!

Please start your own construction thread, so we can see more of your build!

 

[Serjon1]

Feel free to start your own build thread, so we can see more of your project!

I'll figure out how to do it and will post some pictures as I manage to work away... I expect to be finished by July...

 

[johanras]

Hello! Glad you got a response above, I don't remember the exact dimension I had in width for the blocks, but 19 cm sounds right. I hope the pictures I've uploaded help. I used various ovens from Forno Bravo that I liked and checked in step by step during the process. I also have a build thread on that forum where there might be more pictures. Tip number one for making the oven easier and nicer to build is to make a jig that you can use to cut the firebricks at angles that require minimal mortar (just for the tilt angle), tip number two is to find the Excel file from Forno Bravo where you can calculate the number of courses, the number of bricks in each course, and the cutting angles. Tip three, make sure to have a good water-cooled saw. The mortar I think I mentioned in earlier threads was really nice to work with.

I don't know if I would have wanted to do anything differently. I've thought about what it would have been like if I had placed insulation further forward, so that there isn't an angle between the dome and the chimney/arch. I could then have placed more insulation in the angle and plastered over it. The downside is it's not the same dome shape, but it would have avoided areas where water can get in when it rains. Not that it has caused any problems so far. And I would actually like to be able to hide the bricks at the front somehow, and in that case, it would have been built-in and with mosaic over it.
And then there's the matter of oven height, which could have been lower (easier to build around) and whether one should have invested in a better floor, according to previous discussions. In any case, it's a well-functioning oven, and it has started to heat up for the season now.
Send over a link with your build thread when you get started.

 

[Serjon1]

Thanks for the response and tips! Found you on Forno Bravo too!
I think it turned out really nice that the brick is visible and I like the life the contrast against the mosaic creates. I hope to be able to build something similar myself but I realize of course that it is demanding in terms of time, effort, and money. At least the foundation is now finished, the next step is to build the base with lecablock.
All the best!

 

[Serjon1]

Hello! Great that you got replies above, I don’t remember the exact width dimension I had on the blocks but 19 cm sounds right. Hope the pictures I uploaded help. I myself used various ovens from Forno Bravo that I liked and went in and checked step by step during the process. I also have a build thread on that forum where there may be more pictures. Tip number one for making the oven easier and more stylishly built is to build a jig which you can use to saw the firebricks at angles that require minimal mortar (just for the slant angle), tip number two is to find the Excel file from Forno Bravo where you can calculate the number of courses, number of stones in each course, and the cutting angles. Tip three make sure to have a good water-cooled saw. The mortar I think I mentioned in the earlier thread was really nice to work with.

Don't know if I would have wanted to do something differently. Have considered how it would have been if I had placed the insulation further forward so that there wouldn't be an angle between the dome and chimney/vault. Could then have placed more insulation in the angle and plastered over it. Drawback not the same dome shape but would have avoided places where water can get in when it rains. Not that it has caused any problems so far. And I would really want to be able to hide the brickwork at the front somehow and in that case, it would have been built-in and covered with mosaic.
And then there’s the matter of oven height which could have been lower (easier to build around) and whether one should have invested in a better floor according to previous discussion. In any case, a nicely functioning oven and it has started warming up for the season now.
Send over a link with your build thread when you get started.

Hello again!
In an initial thread, you wrote that you planned to use stone wool as insulation but when I look at your pictures it rather looks like you used superwhool. Stone wool is significantly cheaper and easy to find but what did you end up using?
All the best!

 

[johanras]

Rockwool fire blanket, I believe it was 3 cm thick.

 

[Serjon1]

Rockwool fire blanket, I think it was 3 cm thick.

Many thanks for your response! Rockwool fire blanket it is!

 

[Dan_Johansson]

Thank you so much for your reply! Rockwool fire blanket it is!

Superwool (or ceramic fiber) is not too hard to find, but it's more expensive as you said. Additionally, the shipping becomes costly because it is bulky. I bought it from some company located a bit up north and they shipped it relatively cheaply with DHL.. Can't find it now though..

The problem with Rockwool is that the binder used cannot withstand higher temperatures than 250 degrees continuously. The rock wool itself can handle over 1000 degrees, but the binder degrades. This causes the "fluffiness" to disappear. Whether this becomes a problem when rendering an oven, I don't know, but in the worst-case scenario, the insulation might settle, creating an air pocket at the top and compressed rock wool at the bottom.. I've built a wooden "house" over my oven, using a layer of ceramic fiber first (50-100mm), and then Rockwool. However, I initially used only Rockwool, and it wasn't very good when I switched to ceramic fiber next to the brick.

 

[Serjon1]

Superwool (or ceramic fiber) is not so hard to find, but it's more expensive as you say. Additionally, the shipping becomes expensive because it is bulky. I bought from some company located a bit north and they sent it relatively cheaply with DHL.. Can't find it now though..

The problem with Rockwool is that the binder used cannot withstand temperatures higher than 250 degrees continuously. The rock wool itself can withstand over 1000 degrees, but the binder breaks down. This causes the "fluffiness" to disappear. If this becomes a problem when plastering an oven, I don't know, but in the worst-case scenario, the insulation settles, which creates an air pocket at the top, and compressed rock wool at the bottom. I have built a "house" of wood over my oven and use a layer of ceramic fiber first (50-100mm), and then Rockwool. However, I initially only used rock wool, and it wasn't great until I switched to ceramic fiber closest to the brick.

Thanks for the reply Dan!
Maybe I'll have to spend that extra thousand crowns (or more) anyway... you don't dare to take any chances...

 

[johanras]

My plan was to lay ceramic fiber underneath but I couldn't find anywhere to buy it and decided on rockwool, thinking that the temperature on the outside of the dome shouldn't get so high that it would break down the rockwool. But it would have felt even safer with ceramic fiber. I would have chosen it if I had found it at a reasonable price.

 

[Serjon1]

My plan was to use ceramic fiber underneath but I couldn’t find anywhere to buy it and decided on rockwool and thought that the temperature on the outside of the dome shouldn’t get so high that it would break down the rockwool. But it would have felt even safer with ceramic fiber. I would have chosen it if I had found it at a reasonable price.

What do you think about the insulation in the link below?

https://www.kamintillbehor.se/keramisk-isolermatta/isolermatta-1200-grader