Forno Bravo Forum: The Wood-Fired Oven Community

Forno Bravo Forum: The Wood-Fired Oven Community (http://www.fornobravo.com/forum/)
-   Newbie Forum (http://www.fornobravo.com/forum/f2/)
-   -   Newbie seeking advice for hybrid oven... (http://www.fornobravo.com/forum/f2/newbie-seeking-advice-hybrid-oven-15435.html)

Satan 02-22-2011 10:06 AM

Newbie seeking advice for hybrid oven...
 
Has anyone used, or thought about using, styrofoam panels ( panel covintec - Google Search ) for the insulation base of an oven?

Due to the availability, or lack thereof, along with the cost of certain items where I live part time in a small town in Mexico I am thinking out of the box a bit (as far as the traditional methods detailed throughout this great forum).

That being said, my current plans are to go to a local adobe brick manufacturer and ask them to make adobe blocks with molds I will provide them. Typically here in Mexico they either make a cob oven or use blocks made of adobe clay/soil. The shape of the blocks used here for making dome style ovens are called "cola de pato", which is basically an isosceles triangle with the corner (point) of the long end cut off parallel to its opposite side (think of a wedge with the point cut off). Using this form of block uses less mortar. Oh, the mortar I will be using is simply adobe clay/soil.

My issues here are that the town is so small, along with the hassles of obtaining vermiculite/perlite etc. I am trying to think of alternative methods and materials to construct my Pompeii style oven. I'm thinking of constructing an isolated base, as typically done for brick ovens, but using a foam panel (see link above), reinforced with rebar, with a 1 1/2" layer of regular concrete on the top and bottom sides of the panel. Then a thin layer of beach sand on top with wine bottles (yes, I love red wine with my pizza) laying down on their sides with about 1" of beach sand between each bottle (another thermal layer) and then a thin layer of beach sand on top of the bottles. The final layer (the oven floor layer) would be adobe clay/soil mixed with sand (not beach sand) at a 30/70 ratio (the same ratio used to make adobe blocks). It is my understanding, after reading volumes of information in various forums, insulating all sides of the oven is crucial for the efficiency of the oven. Is this insulation overkill or ?

Additional info: The dome of my 42" oven will be constructed using the "cola de pato" style of adobe blocks as mentioned above with an 8" wall thickness. After the adobe block dome is constructed (with a hybrid interior dome height of 18" along with 9" vertical side walls) my plan is to coat the dome with a 6" layer of cob (adobe clay mixed with either sawdust, straw or coffee bean husk (this is the insulation layer). The final layer will be a 1 1/2" layer of adobe and sand mixture (kind of like a plaster coat).

Yes, I'm basically making a cob oven but using adobe blocks instead of the adobe clay.

Any advice you folks can give me would be greatly appreciated.

azatty 02-22-2011 10:56 AM

Re: Newbie seeking advice for hybrid oven...
 
Polystyrene (styrofoam) melts at 240 degrees Celsisus. Since the floor bricks can easily exceed that temperature, it's a bad idea to use it as the base insulation.

If I were in your position, I might do away with the base altogether and build directly on the ground. Part of the reason that insulation is used under the bricks it to prevent the structural slab from heating up and causing problems with the concrete. If you were to build the oven on the ground and set the floor bricks on a bed of sand and fireclay, you could probably avoid the need for as much insulation.

Satan 02-22-2011 11:17 AM

Re: Newbie seeking advice for hybrid oven...
 
@azatty:

Thank you for your quick reply. My unscientific thinking is that the temperature below the oven floor and the sand and bottles not to mention a layer of regular concrete would not reach the melting point of the styrofoam. Again, no scientific data supporting my thinking but it's hard for me to believe the temps can get that hot so deep within the base of the oven.

I've read about people using broken glass or broken red bricks in a base of sand and I've even read and been told by several locals here that a thick layer of salt can provide a good insulating layer although in my brief googling I didn't find much information supporting the validity of salt being an efficient insulating material. Again, one of my issues is the availability and access to fireclay, fire bricks, vermiculite and perlite and thus my search for alternatives.

Building the oven on the ground is not an alternative for me for a variety of reasons, One, the simple inconvenience of having an oven on the ground as opposed to the oven door at a more user friendly waist height. The other is the location of the oven is pretty much set due to the fact that I have already constructed the house and the attached terrace all with keeping in mind I was going to build the oven just off one side of the terrace (patio).

dmun 02-22-2011 12:01 PM

Re: Newbie seeking advice for hybrid oven...
 
Quote:

using a foam panel
Quote:

Then a thin layer of beach sand
Quote:

wine bottles
Quote:

clay/soil mixed with sand
Quote:

a thick layer of salt
Quote:

broken glass
Quote:

broken red bricks
My heart goes out to you trying to source insulation materials in an undeveloped area. Really, it does. But you have come up with almost every bad idea except gravel for insulation I've ever heard of. Even one I haven't (broken red bricks).

I think some of this wild creativity should be expended toward getting some vermiculite or pumice delivered to you. Or having that brick maker make some really porous bricks, mixing a lot of sawdust with the clay before firing them.

Satan 02-22-2011 02:48 PM

Re: Newbie seeking advice for hybrid oven...
 
@dmun:

Thanks for your understanding, believe me it's no fun, at times, living in such an isolated area. You give me more credit than I deserve... The insulating items I mentioned, other than the foam panel, were not my ideas. They were all taken from various forum sites and or from local knowledge here in Mexico.

Your recommendation for asking the adobe block/brick maker to add sawdust to the mix before firing is spot on!. And to think I actually went to a large fire brick factory in Colombia (where I also spend my time) when I was doing the early ground work for building a Rado/Scott hybrid. There I saw them adding sawdust into the mix and I asked the owner what was the purpose for adding the sawdust and he explained that the bricks they were making that day were insulating fire bricks as opposed the the normal fire bricks he typically makes and he went on to explain how the sawdust burns away leaving the brick very porous thus making it good for insulation.

Thanks for the light bulb moment dmun. I will now change my focus and go to the local adobe brick maker and have them add sawdust to the mix and fire some bricks for the use below the oven floor. Hmmmm... Why not use them for the second layer instead of using the cob with straw? (Rhetorical... sort of)

This leads me to ask another question but first my original plan... I was planning on having the local adobe brick/block maker fabricate my blocks without firing them but allowing them to sun dry, as they do with many of their blocks. Now my question.. Do you think instead of having them only sun dried I should have him fire them? And if so why? Is they any benefit or loss for having them fired as opposed to sun dried?

Gravel? Something more to think about.

Thanks for taking your time to respond to newbie questions. I do appreciate it!

dmun 02-22-2011 02:55 PM

Re: Newbie seeking advice for hybrid oven...
 
I don't know enough about adobe to say anything much about it. I think that fired bricks, even if they are not particularly high temperature fired, will not fall apart with exposure to even atmospheric moisture the way mud will. Also, If they are making insulating bricks for you, firing will turn the sawdust into cavities that will insulate better, and not smolder in heat.

Satan 02-22-2011 02:58 PM

Re: Newbie seeking advice for hybrid oven...
 
@dmun:

By the way, kudos to you... What a great idea for a geodesic oven project.

My plan of using the Mexican style "cola de pato" shape of bricks is to use less mortar and ease of construction for dome. What I did not mention in my first post was that not only do I plan to use the "cola de pato" shape of brick, I will also make the mold which will be wedged shaped on four sides. Again, making for less mortar and ease of construction.

Satan 02-22-2011 03:05 PM

Re: Newbie seeking advice for hybrid oven...
 
For what it's worth, my future oven will not be exposed to the elements. It will have a proper roof structure in addition to being on an elevated base.

lwood 02-22-2011 03:43 PM

Re: Newbie seeking advice for hybrid oven...
 
Hi Nata,
I also live in a provincial area of the Philippines where materials are limited. I used red-clay firebrick for my hearth and dome. I would definitely get the fired firebrick because the sun-dried are very soft and will wear quickly. Not sure where you are located in Mexico, but in some of the volcanic areas they mine pumice, which is perlite. If you can source some pumice, that is a good insulator when mixed with concrete, 6:1. The clay bricks with saw-dust may be ok but I don't think they will be that effective of an insulator. Good luck

azpizzanut 02-23-2011 01:12 PM

Re: Newbie seeking advice for hybrid oven...
 
Hello Nata,

Mexico, land of the "horno" but you want to build something different, correct?

An adobe brick maker is nearby, correct? He can mould raw adobe and also fire adobe with straw or sawdust? Wow!! I'd be in heaven with such rich resources available.

Some of the oven building materials you mention are expensive or not generally available in your location. Here in the U.S. we have a saying, "When life gives you nothing but lemons, then make lemonade from them". That is not an accurate quote and I'm sure there will be lot of laughs from others, but my point is the lack of modern materials is not a problem. There should be local knowledge available to make a successful, traditional oven. You could modify a horno with a chimney and have a unique wood fired oven using the basic construction and native materials. Hornos can cook anything that the modern wfo's can cook.

Another benefit of a traditional oven, if it is damaged or you need to fix it then you mix up some adobe and make a plaster repair. Try that with a Pompeii or modular oven !

If you can get regular fire bricks for the hearth then your oven will last a long time, especially if it is covered with a roof. You can use the same fire brick to line the sides and floor of the entrance.

Please ask your brick maker about the recipe for the bricks. I live in Arizona and many makers add Portland cement and, or, asphalt to the brick to stabilize them against erosion. I am sure he wouldn't use asphalt in bricks he fired but other adobe bricks may contain small amounts of stabilizers that wouldn't take well to heat.

If you have an opportunity to visit a large town be sure to look for a Cemex distributor. They have 84 locations in Mexico and they also manufacture refractory bricks.

Best wishes,


All times are GMT -7. The time now is 07:37 AM.

Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
2006/10 Forno Bravo, LLC