Forno Bravo Forum: The Wood-Fired Oven Community

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-   -   just like swampy's (http://www.fornobravo.com/forum/f43/just-like-swampys-15830.html)

zink854 05-02-2011 01:54 PM

just like swampy's
 
1 Attachment(s)
Hello all,
just read through swampys thread and liked his idea. On the last page his oven mold is looking really good. I have a few questions for the pizza oven experts out there. I am a concrete guy by trade so the easiest way for me to build one of these perfect dome ovens is with refractory concrete. The brick domes within this website look amazing, but a little out of my league. Does anyone know if cement fondu will work for a pizza oven dome? If so can you use glass fibers to help reinforce the dome? In swampys last post he was trying to figure out how to build an outside mold. what about building out the dome in a series of layers on top of the interior mold. Each one becoming a little more loaded with fiber? after it has all cured, dismantle the mold carefully and you have your dome? I am new to the pizza oven forum and am in the process of building my first oven . Any help would be greatly appreciated.

reptilazio 05-02-2011 07:46 PM

Re: just like swampy's
 
hi dont know the refractory concrete u are going to use but any that can handle above 1200c i think will serve. the dome dont pass 600c for pizza making i am a professional pizzaiolo and the oven at work was 550c at the dome and 380 to 400 c on the floor for 2 min pizzas i just made my home oven with kaocast m concrete from thermal ceramics and u can make it without a 2 part mold i use stainless needles but i dont think they are really necessary i think its like the fiber u want to use but the concrete itself can support the dome i think i post pics here http://www.fornobravo.com/forum/f43/...ico-15813.html i hope this info help you

dmun 05-03-2011 09:36 AM

Re: just like swampy's
 
I was going to let one of the people who have personal experience with castable jump in, but since no one has I can point out a couple of things. First, refractory concrete isn't easy to work with. Second, it's expensive, particularly when you factor in the cost of the stainless steel needles (not fiberglass) that is the reinforcing medium. Most of the actual experience with castable comes from countries like Australia, where firebrick is irrationally expensive.

One final note: A brick oven isn't hard to build, particularly if you don't cut every brick to shape. Your concrete skills will be more than adequate to the task, especially given that most of us had never laid a brick before beginning our projects.

david s 05-03-2011 01:57 PM

Re: just like swampy's
 
There is a fair bit on casting a dome if you search the threads. To make a mould for a one off I think the easiest method is to build a sand castle covered with wet newspaper. There are proprietary mixes with the appropriate aggregates already mixed in to the correct proportions that are designed for this purpose. Making up your own brew is likely to result in failure for a number of reasons.Best to stick with a premixed product designed for the purpose. The stuff is known in the trade as castable refracory and you should get advice from a refractory supplier.

zink854 05-03-2011 07:30 PM

Re: just like swampy's
 
Thanks for all the advice. has anyone worked with the cement Fondu product i have pictured in the original post? I have acquired 300# and would like to make it work. DMUN thanks for the tip, what do you use to fill in all of the spaces between the uncut brick?

dmun 05-03-2011 07:46 PM

Re: just like swampy's
 
Quote:

what do you use to fill in all of the spaces between the uncut brick?
The first post on this thread has the recipe for "home brew" It's cheap, and amazingly resistant to cracking. It works fine with big joints. It's recommended to use fine silica sand for better workability, and fit on the narrow end of joints.

You have read our plans, right?

As for the "ciment fondu" you probably want to phone up the manufacturer and ask for some engineering support. The place where you bought it may also be of help.

Tscarborough 05-03-2011 08:31 PM

Re: just like swampy's
 
This is what I tell people when they are trying to decide between a concrete driveway/sidewalk/patio versus concrete pavers, "with the pavers, all of the cracks are pre-engineered". What this means is that a monolithic concrete unit is going to crack. Period. It is going to crack. By using unitized masonry units, the cracks are not an issue structurally or (normally) aesthetically.

If you want to use a castable, you have to engineer the structure so that it also has the cracks designed in. Manufacturers do this by casting the dome in 4-8 segments with lapped joints. For an individual to create the molds to do this for a one-off unit is highly impractical both from a cost and time standpoint.

If you have the time and money to do it right, you can certainly build an excellent cast oven if that is your desire, but if your goal is to save time or money, then you are barking up the wrong forest, much less the wrong tree.

Lburou 05-04-2011 08:54 AM

'home brew' using ciment fondu & Home brew Castable recipe
 
Hello Zink :)

I used a' Ciment Fondu' Product by Kerneos Technologies in the mortar mix for my dome. During my visit to our local refreactory, the owner said I could use ciment fondu as the base for a castable mix (their castable recipe is below -As yet unproven in a wood fired oven). I considered it too big of a risk to mix my own castable, I just bought a couple bags of castable mix for my chimney.

The calcium aluminate cement bag is labeled 'Calcium Aluminate cement'. Why I used it: The up side is that a refractory mortar should heat up faster and hold heat better than non-refractory moratrs. My hunch is that it will shorten times to heat the oven and to equalize temperatures -that means using less wood and time in the process- something important to me.

The mortar set nice and hard, but with a few cracks from shrinking during rapid curing (haven't fired it yet). When you omit lime from the mix, there are almost no cracks from the rapid curing.

The 'home brew,' using calcium aluminate instead of Portland cement, sets within 15 to 25 minutes with ambient temperatures between 50 and 75 degrees. Warmer temperatures will shorten that time. Lime will cause the mix to set up in less than ten minutes :eek: I strongly recommend omitting lime from the mix!!

P.S. I read online that Ciment Fondu is a French name for calcium aluminate cement.

P.P.S. I spoke with the owner and his engineer at my local refractory about a 'home brew' castable. Here it is -use at your own risk, to my knowledge it hasn't been validated in a cast oven:
  • 30% Ciment Fondu
  • 60% Aggregate (#6 mesh -sizing 3mm down to powder)
  • 5-10% Fine Sand
  • 5-10% kyanite (crushed, Metamorphosed peri-aluminous sedimentary rock, optional if not available locally)

Lburou 05-04-2011 09:03 AM

Re: just like swampy's
 
Quote:

Originally Posted by Tscarborough (Post 112273)
This is what I tell people when they are trying to decide between a concrete driveway/sidewalk/patio versus concrete pavers, "with the pavers, all of the cracks are pre-engineered". What this means is that a monolithic concrete unit is going to crack. Period. It is going to crack. By using unitized masonry units, the cracks are not an issue structurally or (normally) aesthetically.

If you want to use a castable, you have to engineer the structure so that it also has the cracks designed in. Manufacturers do this by casting the dome in 4-8 segments with lapped joints. For an individual to create the molds to do this for a one-off unit is highly impractical both from a cost and time standpoint.

If you have the time and money to do it right, you can certainly build an excellent cast oven if that is your desire, but if your goal is to save time or money, then you are barking up the wrong forest, much less the wrong tree.

You have an advantage over commercial manufacturers of these ovens: You will build it in place and don't need to transport it. Maybe you could borrow their idea to pre-engineer some cracks to your advantage. :)


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