pompeii oven construction began today

[aikitarik]

For any large enclosure, it's cheaper to coat the dome in a 4-6" mix of perlite/vermiculite & cement (the 6 or 8:1 ratio) and then house it. Loose fill will be somewhat more energy efficient but probably not noticeably with our use. This would probably save you 2/3 or 3/4 of the loose fill needed.

Jim

Jim,

I'm just about at this stage... would it really be more efficient to do the loose fill and no perlite concrete layering? I was planning on a 12:1 mix, about 4-5 inches thick and than using loose fill around that.

My main concern was to prevent perlite dust from getting into the oven and to add a little more structural support around the chimney.

Tarik

[Marcel]

12:1 seems to be a weak mix

(M) Jim wrote:

"For any large enclosure, it's cheaper to coat the dome in a 4-6" mix of perlite/vermiculite & cement (the 6 or 8:1 ratio) and then house it. Loose fill will be somewhat more energy efficient but probably not noticeably with our use. This would probably save you 2/3 or 3/4 of the loose fill needed.

Jim"
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(M) Tarik, if your last post was not a typo, I think 12:1 would not offer enough adhesion. I used perhaps a 7:1 and could not get it to stick to the aluminum foil (hardly a surprise); but even after adding Paul's chicken wire, it fell off. Cement is cheap but perhaps you simply want your cladding to be as "insulatory" as possible.

Ciao,

Marcel

[fdn1]

Reason for aluminum foil?

Jim
Sorry if this question has been addressed previously but I do not remember reading about it in the plans on the internet for the Pompeii style oven. So I was wondering if the major reason for the aluminum foil between the dome firebrick and the Vermiculite/cement cladding is to reflect heat?

[Marcel]

Aluminum foil rationale:

#72

(M) Hi Fred,

You asked:

Jim
<snip> So I was wondering if the major reason for the aluminum foil between the dome firebrick and the Vermiculite/cement cladding is to reflect heat?

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(M) I don't remember who wrote what follows but I saved it. It is one builder's rationale for using foil:


(?) "This is ordinary aluminum foil from supermarket, sold in 2 or 3 widths and thickness, get the stronger one while considering the price as well. This foil has one main role to play. It is not there to reflect heat back; there is no light, why would you want to reflect heat away from cladding? We need heat in the cladding. The foil prevents concrete bonding with firebricks, which is the main reason. Other then that this foil also stops firebricks to absorb water from soft concrete when it is applied. Instead of aluminum foil candle wax or plastic wrap could be used, but it would burn and be felt in the air for the 2 first firings."


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(M) Although I am having difficulty getting the perlcrete to adhere to the foil, in general I agree with that writer. One factor not mentioned there was that foil would also tend to stop any leakage of smoke from cracks in the refractory layer that virtually (or completely) covers the fire bricks.


(M) In the quote above, that builder, I believe, suggests putting the foil between the firebricks and the layer of refractory mortar. In my case, I will have an insulating layer of perlcrete so I do want to reflect heat back to the firebrick. I'm not sure that foil would work as a heat reflector, absent light but the thermal engineers who read this may be able to shed light on that question.


(M) Since placing perlcrete at the top of the dome should not be an adhesion problem, I will, at a minimum, clad as much of the external dome top with perlcrete. When it starts to slide off, I will look for other solutions. I will ultimately house my igloo and pour loose dry perlite over the dome. That will provide a lot of insulation but will not protect my dome from the rain until I get the roof built. The foil placement may, in my case, be an exercise in futility.

(M) If you use the foil remember to start to place it from the bottom up, just like roofing tiles so that any water that gets through will not get under that foil layer.

(M) I believe that not many Pompeii builders bother with the foil but like Paul's adage states, I prefer to "overdo or don't do it at all".

Ciao,

Marcel

[paulages]

marcel,
i have not had any visible problems with an expansion differential between my insulating layer and my refractory mortar/brick layer. granted, mine is a manufactured refractory insulator and not perlcrete, but they should act somewhat similarly. i would suggest that you ditch the aluminum foil and move forward...but i don't mean to talk you out of "overdoing it."

[Marcel]

Foil here is for water (&amp; smoke) shield

# 73

(M) Paul, I'm not really concerned about the "slip plane" but about a water shield and to a lesser degree, a smoke shield. Had I worried about a slip plane, I would have placed the foil between the bricks and the refractory cladding layer where cracking could have structural ramifications. If the perlcrete cracks, and I doubt that it will, there is no real harm done. Still, that's a rhetorical response as I may need to give up on the foil anyway for lack of adhesion. I want to "move forward" but I need to await at least 3-4 days of predicted dry weather.

Ciao,

Marcel

[aikitarik]

(M) Tarik, if your last post was not a typo, I think 12:1 would not offer enough adhesion. I used perhaps a 7:1 and could not get it to stick to the aluminum foil (hardly a surprise); but even after adding Paul's chicken wire, it fell off. Cement is cheap but perhaps you simply want your cladding to be as "insulatory" as possible.

Marcel,

I am basing the decision for using a 12:1 ratio on a post from Alan wherein he suggests it (for the Bread Builders oven) IFF you have enough structural support.

Since I am merely coating the oven, I figure this will be no problem. If I go with this approach, I don't believe I will have the adhesion problem you're describing as I will simply use some hardiboard forms in addition to the chicken wire.

Tarik

[paulages]

hurricane oregon

but I need to await at least 3-4 days of predicted dry weather.

good luck! ... so you'll be "moving on" next july?

[james]

What about renting a big tent to go over the oven so you won't have to wait for the impossible?

James

[Marcel]

Tent, cement, rain came and went but not in vent.

#74

(M) What can I say to Jim and Paul
Who build their ovens dry and tall
Not like mine, so wet and small

Our weather here is not like Gaul
It rains like Hell here in the Fall
But even then I'll have a ball

It's wet here now, and that's my call
Back to work, I musn't stall!
Round the dome I'll build a wall.

Burma Shave


Ciao, Marcel

[ColonelCorn76]

Jim,

I'm just about at this stage... would it really be more efficient to do the loose fill and no perlite concrete layering? I was planning on a 12:1 mix, about 4-5 inches thick and than using loose fill around that.

My main concern was to prevent perlite dust from getting into the oven and to add a little more structural support around the chimney.

Tarik

Using a foil wrap in between the perlite mix & the dome should keep any perlite dust from getting in the oven (shouldn't be a problem anyway but no big deal to eliminate the possibility). The 12:1 mix is probably too dry to use -- 6:1 or 8:1 is fine. Using loose fill on that is probably counter-productive (or at least past the point of diminishing returns). 5" of perlite concrete is the insulating equivalent of about 9' of concrete. For all practical purposes you're not going to need more then that to be able to store enough heat to cook - even overnight.

Jim

[ColonelCorn76]

(M) In the quote above, that builder, I believe, suggests putting the foil between the firebricks and the layer of refractory mortar. In my case, I will have an insulating layer of perlcrete so I do want to reflect heat back to the firebrick. I'm not sure that foil would work as a heat reflector, absent light but the thermal engineers who read this may be able to shed light on that question.

The foil can be a slip plane between the outer mortar "butter" and the insulating layer and the dome due to the differing thermal reactivity of the two materials. If you're using a mix of materials for the insulating layer (e.g. a layer of refractory cement and then one of perlite/vermiculite) then the foil can be used between the refractory layer and the perlite/vermiculite layer simply due to the thermal shock resistance (to cracking) of the refractory cement.

Foil is an optional component by the way and not really necessary. More useful for the fully exposed igloo style oven then the doghouse style.

Jim

[paulages]

roof almost done

the roof is ready to plant...just gotta put some soil up there.

after framing the wooden roof on top of the durarock, i used 2" x 8" lumber to frame in a "curb" around the edges. then i layed pond liner in, cutting a hole for the chimney, using a #8 metal roof style hi temp. chimney flashing to seal around it. folding the liner over the edges, i tacked it to the outside of the frame with roofing nails, and used gable flashing to hide it. at the bottom, the pond liner just spills over into the gutter, and i used a piece of "trex" (recycled plastic 2" x 4") as a soil barrier. a 1/2" gap was left at the bottom for drainage, and aluminum screen was nailed to the trex to help keep soil from eroding through. this was backed with gravel.



top view of gutter line:


showing new overhang...


...by the way the wooden part on the left is not new, but rather part of the pre-existing kiwi arbor, that will now function also as a rain shelter from the backdoor to the oven overhang.

[aikitarik]

I must say, very sexy!

[paulages]

wood storage doubles as doghouse.

perhaps the best multi-use function i have found yet for a giant stone structure in the backyard. seriously, i have to keep convincing myself i'm not crazy everytime i walk up and think, "holy "@^%#" that thing is huge!"