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  #11  
Old 03-31-2014, 09:53 AM
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Default Re: Mini Forno: The Homebrew mix experiment

You are planning on building an entire oven using the homebrew mortar recipe? That recipe is for mortar, not cast refractory. I am surprised I am the first to comment on this. Mortar is not a structural material. I am no expert, but would guess that a full sized oven will fail pretty quickly over the repeated heating and cooling cycles to which it will be exposed - no matter how much "brown rope" you add to the mix.

What you want is castable refractory aka ciment fondu/calcium aluminate cement.
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  #12  
Old 03-31-2014, 01:26 PM
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Default Re: Mini Forno: The Homebrew mix experiment

The jury is out over how long a home brew cast wil last, but there are enough who report it works ok. Two in my local area alone and they're two years old.Homebrew is way cheaper and easier to work with.using a sand mould you can build one in a weekend. So it's very cheap and fast.to build with no guarantees of longevity. Sounds attractive for a home builder to me.
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Last edited by david s; 03-31-2014 at 01:32 PM.
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  #13  
Old 03-31-2014, 03:48 PM
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Default Re: Mini Forno: The Homebrew mix experiment

Quote:
Originally Posted by deejayoh View Post
You are planning on building an entire oven using the homebrew mortar recipe? That recipe is for mortar, not cast refractory. I am surprised I am the first to comment on this. Mortar is not a structural material. I am no expert, but would guess that a full sized oven will fail pretty quickly over the repeated heating and cooling cycles to which it will be exposed - no matter how much "brown rope" you add to the mix.

What you want is castable refractory aka ciment fondu/calcium aluminate cement.
I'm surprised that, having been around long enough to post more than one thousand time, you haven't come across this thread:

http://www.fornobravo.com/forum/f43/...oven-9380.html (brickless dome on a shoestring oven)

It's been done before and, while I agree that the home brew mortar in no way meets the accepted criteria for a true refractory, the brickless oven on a shoestring has lasted well according to michelevit.
Let's face it, its sort of adobe (sand and clay) with some stronger binders added. I know the portland can be expected to break down, but that still leaves the lime and clay.

I'm slowly getting around to doing one myself, just to see how it goes. My plan is to go a little shorter on the Portland cement and a little longer on the lime.
I always thought david s was being pedantic (sorry dave) with regard to using stainless steel reinforcing, but having done some further reading, mine will have either no reinforcing or it will be stainless steel, depending how easy the stainless is to come by.
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Last edited by wotavidone; 03-31-2014 at 04:02 PM.
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  #14  
Old 03-31-2014, 04:12 PM
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Default Re: Mini Forno: The Homebrew mix experiment

I do know about that thread. That builder used a rebar frame which is not the same approach being discussed here. I don't see it as the same approach anyway. And there are many more examples of castable ovens successfully built out of refractory cement than homebrew, if you want to cite evidence points. But my main point is that mortar is not a structural material, nor is it meant to be.

Quote:
Mortar is a very different animal than concrete. Concrete is designed to be used in thicker applications and to reach very high strengths. It achieves its durability through brute force. Mortar is also designed to be durable but achieves its goal through finesse. Its strengths are quite low compared with concrete and it is never used in thick applications. - See more at: What is Mortar?
You can build an oven out of a pile of elephant manure and clay, I guess. Up to the builder. But the conversation deserves an accurate assessment of the appropriateness of the material. Personally, if I was going to go to all the trouble of building forms to build a cast oven, I would spend the couple hundred extra to get the right material for the job. But that is just me.
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  #15  
Old 03-31-2014, 04:26 PM
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Default Re: Mini Forno: The Homebrew mix experiment

It is arguable that the FB Homebrew mortar isn't really mortar either, as mortar is defined by the average bricklayer.

Ordinary mortar, here in OZ at least, is either 3:1 sand:cement, or 3:0.5:0.5 sand:cement:lime. i.e. quite low strength.

With the homebrew being 3:1:1:1 it is, as pointed out by many a masonry expert on this site, far stronger than traditional mortar, even if the hydrated portland cement loses its chemically ccombined water.

Anyway, screw the science, many have used it and swear by it and if it fails little is lost -as davids points out, maybe a wekends work.

Good onya if you would spend the extra few hundred bucks, the original poster stated up front that he was looking to save as much as he could.

A point of order for anyone who does decide to spring for ciment fondu - beware mixing it with lime, apparently this accelerates the set, making it important to place it quickly.
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  #16  
Old 03-31-2014, 04:42 PM
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Default Re: Mini Forno: The Homebrew mix experiment

I make multi sectioned cast ovens for sale and therefore use the best materials I can which includes castable refractory and stainless steel needles, but if I were making one for myself I'd be using Homebrew and cast in one piece over a simple sand castle mould (probably omitting the SS needles they're not mandatory, but do make the casting stronger).
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  #17  
Old 03-31-2014, 04:49 PM
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Default Re: Mini Forno: The Homebrew mix experiment

Quote:
Originally Posted by wotavidone View Post
It is arguable that the FB Homebrew mortar isn't really mortar either, as mortar is defined by the average bricklayer.

Ordinary mortar, here in OZ at least, is either 3:1 sand:cement, or 3:0.5:0.5 sand:cement:lime. i.e. quite low strength.

With the homebrew being 3:1:1:1 it is, as pointed out by many a masonry expert on this site, far stronger than traditional mortar, even if the hydrated portland cement loses its chemically ccombined water.

Anyway, screw the science, many have used it and swear by it and if it fails little is lost -as davids points out, maybe a wekends work.

Good onya if you would spend the extra few hundred bucks, the original poster stated up front that he was looking to save as much as he could.

A point of order for anyone who does decide to spring for ciment fondu - beware mixing it with lime, apparently this accelerates the set, making it important to place it quickly.
Mortar shouldn't be stronger than 4:1
On placement of calcium aluminate castable it goes off already really fast and that's what makes it difficult to manage. Should only mix half a bag at a time IMO because of this. Any lime added will make it start to go off as soon as you've finished mixing it. Cold water retards it and I always use it in the summer.

Last edited by david s; 03-31-2014 at 06:24 PM.
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  #18  
Old 03-31-2014, 05:08 PM
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Default Re: Mini Forno: The Homebrew mix experiment

Actually the “brown rope” will be polypropylene rope added with stainless steel needles (now it will be black rope) see pics

I have read extensively on this subject...From threads at Forno Bravo, other websites, blogs, discussions with pottery suppliers, potters on fireclay, mortar sand mix, etc. and my own experiments on the subject.

I will build a 36x48 barrel style oven with the 3.1.1.1 recipe, stainless steel needles and “ brown rope” now black for less than two hundred dollars in material cost (Sand, Portand, Lime and Fireclay).
The other costs (as each have come to understand) are on reusable materials such as firebricks, blankets, vermiculite, etc.

The mini forno was only build a few weeks ago, but I have pushed it into well over a 1000 degrees for three to four hours on end ( with help and plenty of kindling) for a few days on and off to see if it will break apart. As the days turned into weeks, it performed beautifully (once it seemed to completely dry) it warms up faster and stays hotter longer – No more cracks, etc.

I have confidence it will have a long life based on its respected treatment (slow dry times, fiery starts).Based on an average usage of about 26 to 36 weeks a year (stretching it) a homeowner would fire it up (taking into account heat retention for the next day or so to continue the cooking cycle - Which will be an added plus of days to a given year.) and enjoy for many a moon..


So! Yes! It is well worth it to go the way of the homebrew for those of us to whom wishes to break the status quo.

PS: I was told in a similar fashion that it would not work, last, on when I wanted to make my own concrete countertops for my kitchen. They have lasted over four years and they still look new; at times they have even been mistaken for granite.

To all who read this...Don't blink, just do it.
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Mini Forno: The Homebrew mix experiment-20140330_132926.jpg   Mini Forno: The Homebrew mix experiment-20140330_133154.jpg  

Last edited by Saovicente; 03-31-2014 at 05:37 PM.
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  #19  
Old 03-31-2014, 05:41 PM
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Default Re: Mini Forno: The Homebrew mix experiment

Using this mix for a castable should come with a caveat. That it is a decent low budget alternative to real refractory material.

One should not expect an apples to apples comparison when it comes to performance, longevity or durability, next to a brick or refractory castable oven. The facts about the materials set the limits, not the ability of the person casting the oven.
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Last edited by stonecutter; 03-31-2014 at 06:58 PM. Reason: Word smithing
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  #20  
Old 03-31-2014, 06:28 PM
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Default Re: Mini Forno: The Homebrew mix experiment

Quote:
Originally Posted by stonecutter View Post
Using this mix for a castable should come with a caveat. That it is a decent low budget alternative to real refractory material.

One should not expect an apples to apples performance, longevity or durability comparison to a brick or refractory castable oven. The facts about the materials limit that, not the ability of the person casting the oven.
G'day
Fair comment stonecutter...... I think we will never really know except for those who experiment with this stuff. Its not a commercial material, no ones going to make their fortune with this stuff so it will never ever be tested and a standard made. Its up to these guys
Regards dave
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