Concrete recipe for Weber mod?

[shuboyje]

Jeff, is the water heater pan galvanized?

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.

[Jet_deck]

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.

[shuboyje]

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.

[siouxerbrewer]

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.

[Tscarborough]

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.

[Tscarborough]

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.

[shuboyje]

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.

[siouxerbrewer]

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]

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

[shuboyje]

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.