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**UtahBeehiver** · 03-30-2017, 05:31 AM

The issue with using steel or cast iron is that both of these material have very high thermal conductivity (pulls the heat away). K values (thermal conductivity) for carbon steel or cast iron is about 54 to 58 where as fire brick is about 0.47 so about a factor of a 100. There have been a couple people experiment with steel and it may work for a pizza or so but they lose their heat quickly. Recently there was a perlite or vermeculite/concrete shell completed so that may be an option. David S is our resident casting expert and he has help a lot of FB members cast ovens.

**fox** · 03-30-2017, 08:32 AM

OK, thanks for that!
I have seen a few videos relating the a gym ball, perlite or vermiculite concrete mix design.... if that works that would be very interesting for me...

**Origen** · 03-30-2017, 10:32 AM

Hi Guernseyman! I don't spend a lot of time here, but I couldn't resist responding to you: My mother is from Guernsey! She grew up on Courthill St. Jacques, St. Peter Port! She was a young girl during WWII and had to be relocated to England for a time. I still have a few relations on the island; one aunt recently passed. I have never been, but I just recently convinced my wife we should get over there. You have an extraordinary cow! I recently found a small raw milk dairy farmer near me who keeps a small herd of Guernsey's and another small herd of Jersey's. That is exceptional dairy! OK, that's enough about that.

I am by no means an expert, but I agree with you: fire brick would be brutal expensive for you, I would look seriously at casting a dome. I used some vermiculite concrete on my base, and I also used some perlite concrete elsewhere. In my opinion, perlite might be a better concrete from a workability standpoint. Elsewhere, I have seen information about perlite concrete used in building kilns. That said, if I were casting a dome, I think I would use castable refractory concrete, or a castable mix made yourself (here and elsewhere, you can find the mix ratios). I would suspect you have a masonry supply company on the island (or nearby islands) that has this material. I would think this would be cheaper than fire brick. Although casting seems daunting, there are plenty of great people here to help you. As Utah stated, David S. is extremely helpful regarding casting.

I was actually considering building a second oven, and casting the dome (primarily because it took a lot of time cutting and installing firebrick). I was thinking of making a small "mockup" using a smaller form (maybe 12") to test the process prior to going for it right away. Before I do anything, I need to spend a little more time on the forum!

**fox** · 03-30-2017, 11:01 AM

Hi Origen, what was your mothers surname?
Guernsey is a beautiful place, there are some images here https://www.google.com/search?q=guer...NVxCM:&spf=191

**fox** · 03-31-2017, 03:21 AM

Well I have spent quite a few more hours researching the net.
There are lots and lots of vids about building ovens out of perlite or vermiculite cement mix... it looks to good to be true?
What I cant find are any long term results, I am guessing these type of ovens crack and deteriorate pretty quickly?

**dakzaag** · 03-31-2017, 04:17 AM

The Pericrete and Vermicrete mixes are insulating materials that do not have enough mass or strength to properly form the dome. You want a strong heavy material for the dome to absorb heat and stress from the fire. The insulating mixes are added above and below the dome and hearth to keep the heat from escaping. If you cannot find fire brick, look for solid clay brick and use the softest ones you can find. If you are going to cast the dome and floor, cast it with a dense casting that is refractory in nature.

**david s** · 03-31-2017, 05:14 AM

Originally posted by fox View Post

Well I have spent quite a few more hours researching the net.
There are lots and lots of vids about building ovens out of perlite or vermiculite cement mix... it looks to good to be true?
What I cant find are any long term results, I am guessing these type of ovens crack and deteriorate pretty quickly?

Yes, I would expect them to, Portland cement doesn't like temps exceeding 300C and concretes made of perlite or vermiculite are subject to abrasion damage

**fox** · 03-31-2017, 06:02 AM

There are dozens of videos like this one on Youtube, I have read through the comments but it is really hard to find any long term results....

https://www.youtube.com/watch?v=QA4dim7Nzm4

**david s** · 03-31-2017, 01:41 PM

That's probably because they either don't work well or don't last. They chimney on that oven is poorly designed and way too small in diameter to work properly apart from the materials used in the cast. Notice he didn't provide a video of the oven in operation. I'd expect there'd be smoke billowing out the door.

**dakzaag** · 03-31-2017, 06:40 PM

Build one and show us all how dumb we are!

**fox** · 04-01-2017, 12:40 AM

No point in building one if they don't work or fail soon after completion, in the same vain there is no point in spending a lot of unnecessary money on overbuilding something that wont get a huge amount of use.
I am just trying to lean by asking questions

I am a boat builder by profession & I have been making moulds for over 40 years. I hope my knowledge of form work & composite materials will help me build a suitable mould to produce a dome oven.
If I can source the suitable materials to cast a dome then I will do but, only once I have enough understanding of all the pros and cons.
I appreciate any and all responses, I don't really want to build anything like this without support.

**AndrewT** · 04-01-2017, 04:58 AM

It is all here on the forum discussed many times before.

The word you are looking for is "homebrew"

https://www.google.co.nz/#safe=off&q...rew+castable&*

**UtahBeehiver** · 04-01-2017, 06:22 AM

A member named IronPony did a very nice cast oven mold. Pics of his project are not in a central thread but spread out over several posts. Look under "member list" then "about" to find all of his posts. Like you he did molds for a living, I think he was a die and tool maker.

**david s** · 04-01-2017, 01:46 PM

Originally posted by AndrewT View Post

It is all here on the forum discussed many times before.

The word you are looking for is "homebrew"

https://www.google.co.nz/#safe=off&q...rew+castable&*

Using homebrew as a castable is the el-cheapo way to go. It's longevity is unproven. A superior product is produced using calcium aluminate cement which will endure higher temperatures. There are many proprietary castables available from refractory suppliers, but you need to select a dense castable , not an insulating castable. A complex mould is not worth the effort IMHO, unless you plan on making multiple castings. A simple sand castle form covered in strips of wet newspaper is the easiest and simplest method for a one off casting. Try searching the forum for "cast oven",or "castable",

Here's a start. https://community.fornobravo.com/for...ize#post390588

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