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-   -   Insulating layer over dome (http://www.fornobravo.com/forum/f6/insulating-layer-over-dome-718.html)

Fudugazi 06-13-2006 10:26 PM

Insulating layer over dome
 
I ve seen various ideas re insulating the dome and then protecting it from the elements. I was not planning a roof structure. 4-6 inches of vermiculite concrete over the dome as per the hearth How do you keep this from slumping to the bottom? Someone had suggested tinfoil in there somewhere. Then wire mesh and waterproof stucco. Rock on top of this to blend into the Canadian shield. Does this sound acceptable. Worried about collecting excessive moisture in the dome but i presume the stucco is the answer. thanks. fudugazi on Lake of the Woods How to post pics?

jengineer 06-14-2006 08:45 AM

that's a mouthful.

Tinfoil over the dome - other will correct me if I am off base here. I believe the foil was an attempt to provide a slip plane for the different thermal expansion that will occur as you fire the oven. Unfortunately, that in reality will not work as the oven will ideally expnad like a balloon - equal in all directions. You will get hairline cracks it is the nature of the beast.

The rest is in good order. If you have ever re-modeled a bathroom using real mud (not plaster) then one of the items that is put on the walls is chicken wire. It helps in reducing the slump. Slump factor can be calculated. My dad used to do it 50 years ago when he was on some thin arch dam building projects. You take a calibrated bucket of the concrete/cement pack it down, dump the bucket over and record the slump after a certain time period. It can be likened to an estimation of moisture content. Too much and it slumps big time.

Some builders have built a few fires in their uninsulated "igloo" style ovens to drive off the some of the moisture before adding the insulating layer.

Definately add in the chicken wire, you may want to add some offsets under the wire so that it is not plastered directly to the dome. About 1/2 inch or so off the dome is probably cool. If you find that the insulating mix is slumping let it sit a bit before you place it and on the next batch add less water, gee dude that was obvious. Don't make a smooth surface as you next layer needs a rough surface to bond onto. Again you may choose to run a few fires at this point before adding the stucco. I think a slow buildup of fires at this point is very prudent. If, after xx (litttle help here members) fires and running the oven to cooking temperature you find that the insulating layer is warm to the touch then you nees to add more insulation.

Finally add in layer of stucco, again make it rough if you are going to adhere a stone facade.

Psting pictures are covered by threads withe the name Marcel in them. 2 methods that have been used are:
1. put them into a phto bucket account and then point to then in your posts.
2. shrink them to less than 100kb in size and then before you hit the submit botton scroll down and you will find a button that says "Manage Attachments". With this option the forum software will upload the picutres from your hardrive, floppy disk, memory stick.... You may post a total of 5 attachments with each post and each file again must be less than 100kb

james 06-14-2006 11:23 AM

Moved thread
 
I moved this thread to Getting Started. Keep it going.
James

CanuckJim 06-14-2006 02:18 PM

Waterproof stucco vs roof
 
Fudugazi, JoeEngineer, James,

Sounds like Joe Engineer has the slumping problem well figured out. One proviso, however. If memory serves, the Lake of the Woods area is a lot more rainy (Rainy River) and a lot colder than here in southern Ontario. Building stone over the dome sounds like a handsome idea, but what type of stone? Granite would not absorb much water, but, say, sandstone would. This could lead to freeze-thaw problems. My suspicion is that a shed or pitched roof over then entire structure eventually will be necessary. Hard to tell, though, without more info and maybe a sketch.

Jim (northeast of Toronto)

Alf 06-15-2006 11:38 AM

I would take a tip from most of the books I have on ovens in Europe. Where it rains a lot (here in northern England, Germany, France etc) all of the old outside ovens have pitched slate type roofs to keep out the elements. Also you can have a lot of fun designing and creating your ideal roof.

Alf

Marcel 06-15-2006 12:46 PM

Foil has 4 uses: H20 out, Smoke in, Slip, and heat reflect
 
[QUOTE=jengineer]that's a mouthful.

(JE) Tinfoil over the dome - other will correct me if I am off base here. I believe the foil was an attempt to provide a slip plane for the different thermal expansion that will occur as you fire the oven.

(M) That is only 1/4 of the rationale.

(JE) Unfortunately, that in reality will not work as the oven will ideally expnad like a balloon - equal in all directions. You will get hairline cracks it is the nature of the beast.

(M) And, ideally, that balloon will not burst but expand equally; if not, the foil, which does *not* adhere to the firebrick, will cover any cracks.

(M) The aluminum foil will also keep rain water out if you don't have a tight roof, or if you have no enclosure.

(M) The aluminum foil will also keep the smoke in, though that is only a minor concern.

(M) The 4th reason needs confirmation from a thermal engineer as it is only this novice's theory that it will help reflect radiant, and possibly conduction (not convected) heat back to the dome. If this is not correct, the other 3 reasons are sufficient justification for my use.

(JE) <snip>

(JE) Definately add in the chicken wire, you may want to add some offsets under the wire so that it is not plastered directly to the dome.
<snip>

(JE) Finally add in layer of stucco, again make it rough if you are going to adhere a stone facade.

<snip>

Ciao,

Marcel

james 06-15-2006 01:24 PM

Do builders think the hairline cracks are large enough to let smoke out?

If the answer to that is yes, will foil really keep the smoke in? My thinking is that you should start the curing process to see what the mortar does, and patch it wherever necessary at that point to keep all heat and smoke in.

Either way, I agree with Alf and other postings that you need to build some sort of enclosure that keeps the rain out. That is not the job of the dome. If water has gotten that far, your insulation is wet, and your oven won't cook well.

If you build an Igloo enclosure, the stucco on that enclosure needs to be waterproof. You can seal it, you can paint it with waterproof paint, you can use modern waterproof stucco -- it needs to keep the water out.

And as Alf noted, if you are in a really wet place, you should consider a traditional sloped roof -- an the technology that goes with that. Anything from real slate to terracotta roof tiles, metal, etc. Like your house, it needs to properly shed water.

Helpful?
James

Fudugazi 06-15-2006 09:59 PM

Insulfrax
 
Thanks for your thoughts Where does insulfrax fit in here Is it worth the price does it get soggy if wet?

CanuckJim 06-16-2006 04:56 AM

Aluminum Foil
 
Okay, guys,

One of the benefits of using foil is certainly for a slip plane between the brick and cladding. Don't think it would prevent smoke leaks from cracks. Smoke, like water, will out, no matter. However, the foil also works to even out the temps and prevent hot spots in the oven proper.

Jim

james 06-16-2006 11:34 AM

Hey Jim,

Don't forget that the Pompeii Oven does not use cladding. :) The bricks and mortar act as one -- "see the dome... be the dome".

On the Insulfrax, I think that is up to the builder. It does cost a little more for 1" of Insulfrax vs. 2" vermiculite (similar insulating value), but I like that the Insulfrax is very efficient, and does a good job of keeping heat inside the oven. Most oven producers recommend it and we provide a lot of Insulfrax (easily 1") with the Forno Bravo ovens.

It stands up to a little moisture, but you "really" don't want water that close to your oven.

Build a good, waterproof enclosure, use Insulfrax and your oven will cook great.
James


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