Author Topic: Concrete recipe for Weber mod?  (Read 26717 times)

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Offline Aimless Ryan

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Re: Concrete recipe for Weber mod?
« Reply #25 on: August 22, 2012, 08:06:54 PM »
SB, perlite is basically stone popcorn.  It's almost all air.  Perlcrete contains loads of air.  This is what makes it so light.  It's this lightness that makes it an especially poor material for an oven, because it can't store and radiate back heat.

So basically it's down?
Ryan
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Disclaimer: Don't necessarily believe anything I say here. My brain ain't quite right anymore (unless it is). If I come off as rude or argumentative, that's probably not my intention. Rather, that's just me being honest, to myself and everyone else; partly because I don't have enough time left to BS either you or myself. If you are offended by anything I say, it's probably because you think lying to people (to be "polite") is a good idea. I don't.


scott123

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Re: Concrete recipe for Weber mod?
« Reply #26 on: August 22, 2012, 08:36:07 PM »
Well, I wouldn't make a comforter out of it, but if there was a stone equivalent to feathers, it would be perlite.

Offline siouxerbrewer

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Re: Concrete recipe for Weber mod?
« Reply #27 on: August 22, 2012, 09:08:25 PM »
SB, perlite is basically stone popcorn.  It's almost all air.  Perlcrete contains loads of air.  This is what makes it so light.  It's this lightness that makes it an especially poor material for an oven, because it can't store and radiate back heat.

Pizzahacker has been through many oven permutations, and, honestly, I don't know what he's doing now.  I do know that he's making some amazing pizza, but, unless someone knows exactly what his present oven setup is, I continue to view perlcrete as a losing battle.
I can see that the quest for the "Pizzahacker Perlcrete" recipe has been a challenge for quite a few people.  I have never worked with concrete before but based on what I read in one of those links above there are different densities of Perlite and there must be a perfect blend to accomplish this goal.  I wonder if simply using enough refractory cement with enough air entrainment would eliminate the need for Perlite in this application.  I find it frustrating that so many people have tried unsuccessfully to mimic this. Is there Perlite in firebricks?

Offline Tscarborough

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Re: Concrete recipe for Weber mod?
« Reply #28 on: August 22, 2012, 09:31:15 PM »
Perlite is mostly air.  It is basically volcanic glass that is heated, and it puffs for the same reason popcorn does.  Man-made perlite is available in sheets and boards, called Foam-glass.  It is on the edge for woodfired ovens, but should work well for frankenweber type uses.

Offline Tscarborough

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Re: Concrete recipe for Weber mod?
« Reply #29 on: August 22, 2012, 09:34:15 PM »
Here is what you need to know for perlcrete, different uses use different ratios.  5-6 to 1 for under an oven all the way up to 12-1 for insulation over the top.

http://www.perlite.org/perlite_info/guides/lightweight_insulating_concrete/general/perlite_concrete.pdf

Offline siouxerbrewer

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Re: Concrete recipe for Weber mod?
« Reply #30 on: August 22, 2012, 10:50:38 PM »
Here is what you need to know for perlcrete, different uses use different ratios.  5-6 to 1 for under an oven all the way up to 12-1 for insulation over the top.

http://www.perlite.org/perlite_info/guides/lightweight_insulating_concrete/general/perlite_concrete.pdf
It seems that most people attempting to make this Perlcrete use a type of Perlite designed for garden use.  Those look like large chunks of Perlite; are there smaller chunks that might blend in better making for better structural support?  Also when you speak of mixtures is that Perlite:Refractory concrete mix or Perlite:Portland cement?  Here is a link to a guy who experiments with different mixtures for a rocket oven http://woodfiredpizza.org/Rocket/index.html  I wonder why nobody has seemed to crack this yet?

Offline Tscarborough

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Re: Concrete recipe for Weber mod?
« Reply #31 on: August 22, 2012, 10:52:14 PM »
Normally, perlite will be 1/4" and down with most passing sieve well below that.

buceriasdon

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Re: Concrete recipe for Weber mod?
« Reply #32 on: August 23, 2012, 07:47:46 AM »
That is so cool that someone actually built a rocket oven! Too bad I didn't see any pictures of pizza baked in it. Thanks for the link.
Don

Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #33 on: August 23, 2012, 09:47:52 AM »
It seems that most people attempting to make this Perlcrete use a type of Perlite designed for garden use.  Those look like large chunks of Perlite; are there smaller chunks that might blend in better making for better structural support?  Also when you speak of mixtures is that Perlite:Refractory concrete mix or Perlite:Portland cement?  Here is a link to a guy who experiments with different mixtures for a rocket oven http://woodfiredpizza.org/Rocket/index.html  I wonder why nobody has seemed to crack this yet?
Because there's nothing to crack.  Perlite is an insulator, and mixed with Portland at the ratios already mentioned it works great.  No matter what you mix it with perlite is not a hot face and it does not have thermal mass.  I don't know why this topic always comes up. 
-Jeff


Offline siouxerbrewer

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Re: Concrete recipe for Weber mod?
« Reply #34 on: August 23, 2012, 04:34:49 PM »
Because there's nothing to crack.  Perlite is an insulator, and mixed with Portland at the ratios already mentioned it works great.  No matter what you mix it with perlite is not a hot face and it does not have thermal mass.  I don't know why this topic always comes up. 
I think this topic comes up frequently because as far as I can tell, nobody has been able to successfully replicate the Frankenweber. People's attempts at replication usually result in a lightweight oven that crumbles to pieces, or an extremely heavy, not so portable beast. The idea of a portable WFO is awesome esp when one lives in an apartment.

Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #35 on: August 23, 2012, 05:52:47 PM »
For many reasons I and others have explained many times a luggable wood fired oven isn't feasible in my opinion.  Gas makes much more sense because you do not lose oven space to the fire.  The lbe is a luggable gas fired high temperature pizza oven, so again, what is there to crack?  I'm not being a jerk, I just strongly feel these efforts are a waste of time.  Thezaman had an oven successfully built by a professional.  He found it doesn't work due to lack of mass.  It works great for a short time until the temperature plummets.
-Jeff

buceriasdon

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Re: Concrete recipe for Weber mod?
« Reply #36 on: August 23, 2012, 06:17:27 PM »
« Last Edit: August 23, 2012, 06:35:06 PM by buceriasdon »

Offline Tscarborough

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Re: Concrete recipe for Weber mod?
« Reply #37 on: August 23, 2012, 08:07:00 PM »
The problem is that you are trying to accomplish 2 seperate functions by a compromise. You need refractory mass and you need insulation. As a rule the two are mutually exclusive.

Also, refractory materials are inherently brittle and prone to failure at thicknesses under 3 inches. For a stationary unit 2" is doable but for a mobile unit more specialized and technically exact materials are needed.

Then you need a couple of inches of insulation and some sort of protective coating over that, since refractory insulation is both brittle and friable. 

Formwork needs to be slick and non-absobative, and must also be built so that it can be easily removable and possibly reusable.

In short, good luck with that. 

Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #38 on: August 23, 2012, 08:14:23 PM »
I've been thinking about this a lot today.  Instead of being negative and just telling you guys this won't work I've got something constructive to add.  Here is a simple design for a luggable oven that would work if you could deal with the space constraints:

1. Start with a water heater drain pan like this one:
http://www.lowes.com/pd_317905-11713-QP-28_0__?productId=3126917&Ntt=water+heater+pan&pl=1&currentURL=&facetInfo=

2. Use the pan as a base and cast a 4" layer of 6:1 perlcrete.  Maybe even add handles to the pan before casting the insulation layer.

3.  Get a round kiln shelf like this one:
http://www.axner.com/cordierite-shelf-21roundx34.aspx

Place the kiln shelf on top of the perlcrete centered.  This is now your ovens hearth.

4.  Form a dome from wire mesh 6" larger in diameter then the kiln shelf.  For the shelf above the dome would be 27" diameter.

5.  Using wire buttons attach 2" ceramic fiber insulating blanket to the inside of the wire dome.  Here are blankets and buttons:
http://www.axner.com/ceramic-fiber-buttons.aspx
http://www.axner.com/superwoolfiber-2thicksoldpersqft.aspx

6.  Inside of the ceramic fiber blanket form a 1" layer of dense castable refractory.  Something like KS4-V plus would work and can be obtained from any of these locations:
http://www.hwr.com

7.  Cover the outside of the dome with stucco over the wire mesh.

You now have a small lightweight low mass fully insulated pizza oven.  It should hit high temperature fast and easy with the proper balance of heat that bottom heat source ovens lack.  With a low enough dome(maybe in the 8" range) you might be able to get enough top heat with a small enough fire to cook a 12" pizza, but it would be tight.

Here is a crude drawing of the basic idea.


  
-Jeff

Offline Jet_deck

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Re: Concrete recipe for Weber mod?
« Reply #39 on: August 23, 2012, 08:16:48 PM »
Jeff, is the water heater pan galvanized? :D
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Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #40 on: August 23, 2012, 08:21:12 PM »
Jeff, is the water heater pan galvanized? :D

Yup, but under 4" of 6:1 perlcrete it will never get hot enough to be an issue.  If it get's 10F over ambient I would be shocked.
-Jeff

Offline Jet_deck

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Re: Concrete recipe for Weber mod?
« Reply #41 on: August 23, 2012, 08:21:59 PM »
Yup, but under 4" of 6:1 perlcrete it will never get hot enough to be an issue.  If it get's 10F over ambient I would be shocked.

Well played.
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Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #42 on: August 23, 2012, 08:25:28 PM »
Well played.

Yup and I say this with confidence, my oven sits atop galvanized metal decking with just a bit more perlcrete and I have never recorded a temperature above ambient, and I check every time I fire the oven.
-Jeff

Offline siouxerbrewer

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Re: Concrete recipe for Weber mod?
« Reply #43 on: August 24, 2012, 06:35:20 PM »
I understand that Perlite is an insulator and that TRADITIONALLY the Perlcrete insulation layer is added as insulation over the refractory layer.  If Pizzahacker didn't have success with his version of this oven this conversation would be over and done with; BUT he did achieve this goal in spite of conventional wisdom.  I want to figure out how he did it or find a viable alternative.  Saying that it can't be done when in fact it has been done, doesn't get us anywhere.  Maybe he did a very thin layer of refractory with a very thin layer of insulation, and compensates for the lack of thermal mass by having a larger fire.  Maybe the key is to use a very fine grit of Perlite in the mix.  I don't know but it might be time to check with a concrete mixing forum?  IF we are successful with this build I'll post the results in detail here.

Offline Tscarborough

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Re: Concrete recipe for Weber mod?
« Reply #44 on: August 24, 2012, 08:03:00 PM »
I have tested all the mixes, and tested various thicknesses of refractory backed up with perlcrete.  If you could do centrifugal casting and get an even thickness of refractory, then perlcrete, then refractory, it is doable.  It is doable in sheets, and even for oven doors (what I used it for).  For a <2" round casting, good luck with that, you will get either an uninsulated unit, or a low mass unit, but not both.

My guess is that he has an uninsulated mass on the frankenweber, and that is certainly doable.

Offline Tscarborough

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Re: Concrete recipe for Weber mod?
« Reply #45 on: August 24, 2012, 09:09:22 PM »
Current door, #4

I did the edges and the interior surface with a mix of 3-1 heatstop/perlite, then filled it in with a mixture of 1-3 heatstop/perlite, then put a half inch of 1-1 heatstop/perlite on the exterior. I made a rib vertically in the center, and when it hardens will cut it in half at a 45 (more like 20) degree angle for a two part door.  It is 2" thick.

Front and back pics.

It works well, but does get hot at the top.

Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #46 on: August 24, 2012, 09:55:16 PM »
Earlier I looked up everything I could find on pizza hacker, from videos to pictures to interviews.  To me it looks like his original franken weber was a lighter perlite mix, maybe 3:1 or so with a dense firebrick floor.  His newer pizza forge looks to be a much denser mix, I'd venture to say something close to 1:1.  It also looks like the floor in the new oven is made of this same mix.  That mix is really sitting in no mans land, too dense to be an insulator, but not very conductive for your thermal mass.  It's use in the floor is probably part of the key to his success.  By putting this poor conductor right on top of the coals it probably helps to balance the heat. 

I've said it many times, but haven't said it here in the last few days, I think you are better off ditching the weber grill no matter which route you go.  Building inside a webber adds extra constraints that you don't really need.  By building a slightly larger oven like I showed you can have a traditional setup with mass and insulation and just as much cooking space.  I have not built one of these mini ovens myself, but have directed others to this route in the past who have had very good results.  On the flip side I've seen many try to emulate pizza hacker in the past and fail.  The decision is your, and there are plenty of people here who will try and help either way, we are all just trying to give the best advice we can.
-Jeff

Offline siouxerbrewer

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Re: Concrete recipe for Weber mod?
« Reply #47 on: August 27, 2012, 12:17:49 AM »
It also looks like the floor in the new oven is made of this same mix.  That mix is really sitting in no mans land, too dense to be an insulator, but not very conductive for your thermal mass.  It's use in the floor is probably part of the key to his success.  By putting this poor conductor right on top of the coals it probably helps to balance the heat. 
I think this is probably right on.  I'm starting to think that the LBE might be the way to go.  So many people have tried and failed at this and it might be more trouble than it's worth for now.  Hopefully some day I can afford a house or a place that will allow me to put in a real WFO.

buceriasdon

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Re: Concrete recipe for Weber mod?
« Reply #48 on: August 27, 2012, 08:49:54 AM »
I've often wondered why light weight insulating firebrick has not been used to construct the sides and top of the oven much like a ceramic pottery kiln. I do like Jeff's sandwich idea.
Don

Offline shuboyje

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Re: Concrete recipe for Weber mod?
« Reply #49 on: March 30, 2013, 09:45:13 PM »
Recently I had some questions about the potential design I posted here which are easier answered with a picture, so here is an updated drawing that shows how I personally would actually build an oven like this.
-Jeff