Author Topic: Barrel style brick pizza oven  (Read 3509 times)

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Offline Jackie Tran

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Re: Barrel style brick pizza oven
« Reply #20 on: August 14, 2013, 10:33:12 AM »
Does the vermiculite/portland cement base not act as an insulation layer?  If so, is it not enough? 



Offline stonecutter

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Re: Barrel style brick pizza oven
« Reply #21 on: August 14, 2013, 10:36:44 AM »
Does the vermiculite/portland cement base not act as an insulation layer?  If so, is it not enough?

It does, but it is not as efficient as ceramic fiber board.  Also, a higher ratio of portland in the mix will lower the insulation property, but raise the compressive strength.

If there is limited space, then the ceramic is the way to go.  As an alternative, mineral wool works well too....I have used it on all the ovens I have built with one exception.
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Look at a stone cutter hammering away at his rock, perhaps a hundred times without as much as a crack showing in it. Yet at the hundred-and-first blow it will split in two, and I know it was not the last blow that did it, but all that had gone before.
Jacob August Riis

Offline woodchipper

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Re: Barrel style brick pizza oven
« Reply #22 on: August 14, 2013, 05:56:31 PM »
Stonecutter-I've been using Westbrook Block, but I just bought alot more insulation from the link listed previously in this string.
Your idea of using splits sounds pretty good.  I'm trying to imagine if giving up that thermal mass is a good trade.  Its not like the food has a high thermal capacity though so maybe giving up brick for insulation is a good plan.  Certainly the floor will come up to temp quicker.

Offline stonecutter

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Re: Barrel style brick pizza oven
« Reply #23 on: August 14, 2013, 08:44:00 PM »
More insulation will make your oven perform better, at this point you need as much as possible.   For pizza splits are just fine,  and moderate baking too.
http://oldworldstoneandgarden.com/

Look at a stone cutter hammering away at his rock, perhaps a hundred times without as much as a crack showing in it. Yet at the hundred-and-first blow it will split in two, and I know it was not the last blow that did it, but all that had gone before.
Jacob August Riis

Offline breadstoneovens

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Re: Barrel style brick pizza oven
« Reply #24 on: August 15, 2013, 09:08:46 AM »
Just as quick note, ceramic fiber provides the best result for insulation. Mineral wool as stonecutter mentioned works well but if you fire the oven at a really high temp it looses some of its property.
What I recommend is to not use is vermiculite or perlite mixed with cement alone. Over time it tends to crack and then you have an heat leak in your insulation and it destroys the above enclosure materials.
I just did a repair on a trailer from another company were they only use 1" of fiber blanket and then vermiculite. Even if there was diamond mesh in the vermiculite it cracked through and the enclosure materials just deteriorated rapidly due to the heat it was exposed to.
Despite what many construction guides and books say, if you are going to use vermiculite it should be to shape the dome of the oven and above a minimum of 2" of fiber blanket, but more is better.
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Offline Tscarborough

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Re: Barrel style brick pizza oven
« Reply #25 on: August 15, 2013, 10:32:52 AM »
Or used loose.  That is the best possible state for perlite or vermiculite as insulation over an oven.

Offline breadstoneovens

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Re: Barrel style brick pizza oven
« Reply #26 on: August 15, 2013, 11:09:08 AM »
Or used loose.  That is the best possible state for perlite or vermiculite as insulation over an oven.
^^^
Or perlite loose as well.
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Offline stonecutter

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Re: Barrel style brick pizza oven
« Reply #27 on: August 15, 2013, 06:33:30 PM »
Loose over the oven is better, yes.....but woodchippper was talking about insulation under the floor brick. Can't use loose vermiculite or perlite that way.
http://oldworldstoneandgarden.com/

Look at a stone cutter hammering away at his rock, perhaps a hundred times without as much as a crack showing in it. Yet at the hundred-and-first blow it will split in two, and I know it was not the last blow that did it, but all that had gone before.
Jacob August Riis

Offline woodchipper

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Re: Barrel style brick pizza oven
« Reply #28 on: August 17, 2013, 04:49:53 PM »
Okay- After 1-week of research and help from this blog (especially Stonecutter) I have redesigned my oven plans.   As you may have read earlier, I was in the middle of building my copy of a "kit" oven that everyone seems to be familiar with, then I ready PeteH's woes about his finished version.  I thought I would make a post with a description of how I believe I will solve most of the issues with this design.  From here on I will refer to the design that PeteH and I used as BWO.  I think everyone who knows the design knows what that stands for.  Below is a list of my departures from the BWO design.

2" of ceramic board below most of my oven floor  with a minimum of 1" (I am stuck with some areas at 1" only as I already had some vermiculite/concrete  poured before discovering I was on the road to ruin).
2" plus of vermiculite/concrete under the ceramic board.  I have learned not to machine mix this as it can compress and break-down the vermiculite too much.   I also learned that a higher ratio of 5:1 can still support an oven yet obviously offers 25% more insulation value.
1" of ceramic board around the perimeter of the floor brick (I have not read about anyone paying attention to this detail yet.)  Conduction can occur here, and it is easily prevented.
The floor, will be splits,  not full size bricks.   What I lose in thermal storage, I gain in insulation below and in thermal response.
The "Barrel" will have one fewer vertical course and the arch will not be a half-circle, but a flattened parabola.  This is to optimize the oven for pizza by lowering the ceiling and increasing the radiant transfer.  Radiation on a surface is inversely proportional to the square the distance from the source.  The flattened parabola shape will project radiation over an area, a circular arch theoretically reflects to a line.
I will minimize mortar exposure to the inside of the oven with bricks edge to edge on the inside were possible.  The BWO design promotes as much as 1/2"-thick mortar lines on the oven interior.   Use firebrick for the oven interior, not mortar.
Bevel bricks to maintain the refractory mortar thickness to less then 1/2" even at the outer edges of the bricks forming the curves.  Even high performance refractory mortar will crack if larger than that.
The front facade of my oven will be thermally broken from my oven brick by a 6 mm ceramic paper I will adhere to the firebrick.  This is another often overlooked point of conduction.  (There will  be a 6 mm grout line of refractory mortar that seals this ceramic paper edge from the opening arch.  I cannot see a way around this small thermal bridge).
My finished design has a decorative "box" enclosing the actual oven.    This will allow me 4" of ceramic blanket around the barrel and at the back wall.
The internal oven structure will be thermally isolated from the decorative box at all points. This is including under the floor and the edges of the floor (excluding the floor at the opening to a flush outer shelf)   Super minimal conduction areas.
When the decorative "box" is ready for the roof I will completely fill the cavity with vermiculite before roofing.  Thickness for the vermiculite will range from 1/2" to 6 inches depending on localized geometry.
There will be a removable door (not hinged) for the oven mouth with an adjustable vent.
There will be a infinitely adjustable damper on the chimney.

Offline shuboyje

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Re: Barrel style brick pizza oven
« Reply #29 on: August 17, 2013, 05:26:37 PM »
How to you plan to buttress your new arch profile?  In my opinion the problem with compound curves is that they create outward force at multiple points, which is very hard to account for.  That is why I personally think simply curves that focus all the force at one point are the best. 
-Jeff


Offline peteH

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Re: Barrel style brick pizza oven
« Reply #30 on: August 17, 2013, 08:31:07 PM »
So  it has been a few weeks since my original post and i appreciate the feedback and sidebar topics it has generated, i have learned quite a bit.  I wanted to update you on  all on my modifications and pizza attempts.  I started with closing off the opening and building a removable door out of 3/16" aluminum.  These modifications have been very helpful.  I also switched my dough to TL's new york style dough.  This suits my lower oven temps very well.  I had friends over last weekend and baked 8 pizzas with a nice light crispy crust that is soft on the inside.   The mozz and the toppings cooked very while the pie was on the hearth the whole time, no doming needed.  Anyway, i wanted to say that i think the pizzas i am making now in my brick oven  are better than the pretty good pies i was creating in my electric indoor oven a few months ago. 

Offline nachtwacht

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Re: Barrel style brick pizza oven
« Reply #31 on: August 18, 2013, 07:44:51 AM »
Did you end up putting insulation on top of your oven ? If not, that would help you a lot.

The suggention here also was that the 2 inch fermicrete floor you have would not be to good an isolator. Next time you fire up your oven, check under the oven how warm it is getting. It should not be getting warm... Even though 2 inch is not a whole lot, it is insulation so it should help somewhat. If you add some ceramic fiber on top of the oven (3 inch preferable) I would think your oven should do a lot better.

It will not help you with the cooling down floor after baking a pizza though. This happens with all ovens, even with the best isolated ones (allthough they might suffer from it less than yours). Your oven is probably to small to be baking the 2nd pizza at a different place ? That means you just have to wait a little. When you cook a pizza, it will "take away heat from the floor" and in that spot your floor will cool down. You have to wait a little so the heat will get back into it (your fire will help with that but also the stored heat in the stones will spread and make the cold spot hotter)

You do want fire in your oven while you are baking ! Hot ambers is not enough. You do not want a big fire, just some flames licking the ceiling.

Last problem I see wich you can not do anything about anymore, you used 2 rows of bricks for the "roof" ? If so, you created a lot of thermal mass for your oven. this is great for keeping heat in (if you insulate) but it will take a long time to get hot. Great for baking bread the next day though, you should give it a try :)

I had a very simular oven like yours but with insulation on top and I was able to cook pizza in under 2 minutes. That were the first ones going in though. The pizza party's we had with 30 to 40 pizza's, the last pizza's always took more like 3 to 4 minutes.

Offline peteH

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Re: Barrel style brick pizza oven
« Reply #32 on: August 18, 2013, 09:25:13 AM »
Thanks for your input, appreciate it.  I did feel under the oven the last time i fired and it was only slightly warm to the touch, my IR gun read 90.  I have considered and priced out fiber board and fiber blanket an was going to wait to decide if i need it.  As i mentioned, the pizza's last time came out really good and i feel i have good equilibrium between top and bottom cooking.  I worry that if i add insulation to the top, the toppins and mozz will overcook before the crust is done, thoughts?  I have thought about the suggestion of placing 1" of fiber board over the current hearth bricks and then covering that with splits.   Again i have fired it about 6 times and i think i have to have atleast 15 uses under my belt before i consider a major change which will require me to relearn the cooking properties of the modified oven.  I am firing it up tonight for some friends and will post a pic of one of the pies.  Thanks again for all the constructive posts.

Offline nachtwacht

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Re: Barrel style brick pizza oven
« Reply #33 on: August 18, 2013, 09:54:11 AM »
If it only reaches 90 then I think your bottom insulation with 2 inches of fermicrete is just fine. Sure, it could have been better but I would not worry to much about your bottom insulation then.

I would definatly insulate the top though. It will save you a lot of wood with the warming up process. A lot of your heat is now lost at the top. My first pick would indeed be fire blanket. It is expensive indeed but I think it is worth it. Other ways of isolating are not as easy to do.

You could try to get some cheap insulation like fiberglass just to give it a try. You can not keep it there, but just to see for yourself the difference it will make. No idea how long it now takes you to get your oven warm but it will help with that and it will also help a lot with keeping it hot so you can bake longer.

There are some other much cheaper ways to isolate. You could also put fermicrete on top of your oven or things like airated concrete or expanded clay. All a lot cheaper but a little more work. I think it will be worth the work though.

I am curious how hot your dome is getting. If you do get some readings, make sure to temp it at the start, halfway, end but also like 1 or 2 hours after you are finished.

Offline Pastorryanhayden

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Re: Barrel style brick pizza oven
« Reply #34 on: August 25, 2013, 02:57:26 PM »
Here's what I did and it works fine for pizza.  I closed of the chimney with refractory cement and firebrick pieces,, then I built a Rado style brick hood in the front of the oven.  I have no problem getting the walls to 900-1000 and the floor to 750 in 90 minutes to two hours. (But I only have one course of outside brick and CF blanket.)  I too am planning on boxing mine in and filling the cavity with perlite.
I haven't tried baking anything besides pizza  in it yet, so I can't comment on long term heat holding, but I made 10 pizzas last night in an hour and all of them cooked perfectly, far better than my conventional oven.   I've also cooked steaks and some other dishes in it with great results.
If I can't bake in it, (which, I really can't see happening as it seems to hold heat fairly well even without a door)  I may try adding a fiber floor, but right now I am a happy oven owner.

Offline woodchipper

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Re: Barrel style brick pizza oven
« Reply #35 on: August 25, 2013, 06:02:50 PM »
Here's an update on my oven progress.    I am throwing out my parabola idea based on shuboyje's comments, got scared about the support structure.  But I did reduce the height of my arch by one course.
I just laid the first 3 courses of each side of the barrel today, after insulating and laying the floor yesterday.
Over the past week I realized that there is another weak facet of the original design.  The masonry chimney is a just a big conduction conduit out of whatever insulation house you build.   I am changing my design to a double walled stainless steel flue.   Luckily I have sheet metal equipment at my business and can custom fabricate a flue that will have minimal conduction contact, a tall height for good draft and an integral damper for control.
Took some pictures today, but I am too lazy to transfer them now.  I will post full pictures, and possibly a CAD cross section of the design when I am done.

Offline Pastorryanhayden

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Re: Barrel style brick pizza oven
« Reply #36 on: September 02, 2013, 10:43:04 AM »
I've tested the bottom of my oven when it's going full blaze and its 100 degrees or less.  After cooking at lunch time and putting the door on, it's about 250 degrees the next morning.  So I'm not complaining about the heat retention.  (I haven't insulated my door or the patched chimney yet, so that might improve things too.)

My only complaints with my oven right now are: it's too small (but that's my own fault) and its ugly as homemade soup, but I'm planning on fixing it by building a roof and enclosure.


 

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