Starting my 2nd pizza oven in Los Angeles

[seth]

About 10 years ago, I heavily stalked these forums for my first pizza oven build. It was a 27" oven, on an 8-1 perlite base, firebricks set on sand in a herringbone pattern for the oven floor, and a done of 50% by volume of fired clay grog/ fireclay. Covered that with a 2" durablanket, then covered it all with more 8-1 perlite. As I'm somewhere that doesn't freeze, I left the perlite as the final covering. (I remember reading here that perlite mix can get waterlogged and if that water freezes it can be a problem)

I've been unbelievably happy with that oven. And it's held up fantastically over the past 10 years. The insulation on the top is incredible (stays under 100F when the inside is 800+F), and it holds heat like a champ. The interior walls haven't cracked at all over the years. But I'm looking for at least 10" more interior oven space. So it's time to rebuild. And I've returned to these forums for some wisdom.

My original build was based on this - http://fornoeconomico.blogspot.com/s...&by-date=false
But I'm reading all about Cast refractory builds. And I had a few questions that I wasn't able to find on the forums after a few hours searching.

1) Has anyone else used the fireclay & fired clay grog and can compare it to castable refractory cement? When I looked 10 years ago, there wasn't much talk on the forum about refractory cement, but there were more than a few builds using fireclay/grog. Is there a reason I should move away from my previous method? (ease of use? Better results?)

2) what's the consistency of commercially purchased refractory cement. Is it adjustable by how wet I make it? Can I still use it oven a sand dome like the clay ovens? Does my sand dome have to be firmer than it would be for a clay oven dome?

3) Is it better to cast it in pieces? I see that some people like to create a small heat break from the inner oven door to the chimney & outer oven door. But outside of that, is there an advantage to breaking up the dome into multiple pieces?

I'm sure there's other questions I'm not thinking about.

Here's some photos from my previous build. I built it into a low planter, which I love. I can sit with people, eat and cook all at the same time. Works great for my life. Only problem in the original build was that the dome sank a little, so I had to lose the nice arch for the door I built. And this time, I want to add a chimney and push the oven lip closer to the edge of the planet area.

Thanks a ton for all the help in the past from all the posters on Forno Bravo. So many of my great evenings with friends, wine and oven cooked food I owe to you.
Seth

[david s]

A mix of fireclay and fired clay grog works ok but does not contain any cementious material in the mix. This results in a pretty hard material, but as the temps we fire to are insufficient to sinter the material, (that begins north of 573C) it is not as hard and durable as those containing cementious materials. Calcium aluminate cement is pretty good and will withstand pretty high temperatures well in excess of the range in which we fire. However it is quite expensive. Whereas normal OPC begins to break down at temps exceeding 300C, which is well within our range. Hydrated or hydraulic lime is good for around 500C, so if used in conjunction with OPC, has proved adequate for wood fired ovens. Likewise the use of sand instead of fired clay grog is also adequate for the temperatures to which we fire. The problem with sand at high temperatures (900C+) is that it has a tendency to melt, particularly in the presence of some fluxes, into glass. Fortunately this is also out of the temperature range to which we fire. For these reasons the homebrew of 3:1:1 sand, OPC, hydrated lime, powdered clay has proved adequate and actually superior in some respects to refractory mortar or castables that contain both calcium aluminate cement and high temperature aggregates that are not really required for our purposes.
If the OPC fails, the lime takes over and if that fails the clay takes over. Any powdered clay should suffice. Fireclay for a potter is a different material than fireclay for a mason. For a potter fireclay is a clay that can withstand very high temperatures (1200C+), whilst fireclay for a mason is the cheapest clay that can be used to make a mortar more sticky. pretty much any clay will do, but it should be powdered so it distributes evenly in the mix. Just avoid Bentonite as its extremely small particle size leads to excessive shrinkage resulting in shrinkage cracks. All clay shrinks and produces this problem, but Bentonite way more than any other. Hope this info helps. There are quite a number of excellent builds on this forum which have employed homebrew castable.

Just another pick up from your build, an 8:1 perlcrete insulating slab has generally been found to have insufficient strength to support a heavy oven. A 5:1 mix is better although has a reduced insulation capacity. The insulating mix over the dome however, as it is not supporting the weight of the oven, is better to be much leaner to maximise the insulation value. I find a 10:1 mix is about as lean as I can go and still have the mix reasonably workable as well as having sufficient strength. It produces a mix that is firm enough to apply a cement render onto.

Your question re commercial refractory castable, yes you can use it, but it is expensive and the stuff goes off fast, so you may risk wastage. It also contains high temperature aggregates that are not required. It is made up to a workable consistency by adding water, just like homebrew, until it reaches "ball up consistency". ie throw a ball of the mix 2 ft in the air and it shouldn't break up but you can catch it again.

A one piece cast is far easier, but as any large refractory casting is more vulnerable to cracking due to uneven heating and therefore thermal expansion, multi sectioned castings are more inclined to be crack free. However, as it's a dome it can't collapse and will remain workable pretty much for a life time. If using the "cast in situ" method no relocation and reassembly of the casting is required. This is a huge advantage and saves lots of time and effort.

Allowing the inner oven to expand and contract inside the outer shell and decorative arch is good insurance against them cracking from expansion pressure.

[seth]

Thanks a ton for your thoughtful reply. I'm going to reach out to Zartech (used to be wester industrial ceramics) and see what they have as I debate between a home-brew vs. commercial, see what they have as well.
Also, I really valued the pictures you took of the thermal break and chimney design on one of the posts here. Thanks not just for your direct suggestions, but also the wisdom you've added to the forums in other posts as well.

[AndreasP]

Seth,
Let me know how you get along with you research. I am in Los Angles as well and am also considering to build a Pizza Oven. I am thinking of casting it out of Homebrew mix, still trying to figure out exactly how much material I need and where to get it.
Any advice would be much appreciated.

[AndreasP]

seth , here is what I have found so far:

Thompon's building supplies has

• multiple types of sand
• hydrated lime - 50lbs @ $14.48
• powdered fire clay - 60 lbs @ $7.41
• Firebricks - $1.80 each (or maybe $1.40, the person I talked to wasn't sure)

I am struggling to find Vermiculite. I found DryStall, which is a pumice type material and I have seen it mentioned in this forum as well. The only place I found it was
Kruse Feed - La Habra

• Dry Stall - 40lbs @ $19.10

ebay:

• Refractory Reinforcing 1" 430 Stainless Steel Needles - NOT SURE THEY ARE THE RIGHT ONES, they have waves - 10 lbs @ $35 + $15 shipping
• Polypropylene fiber for reinforcing concrete cement mortar 2.2 Lbs - NOT SURE THEY ARE THE RIGHT ONES, - 2.2 lbs @ $28.99 free shipping
  • They seem to be mulitple fibers together
  • I read that David was recommending Sika PPM 48/19. I did send SIka US a question on availability

Forno Bravo:

• 1" ceramic insulation blanket - 50 sft @ $79+ $25 shipping
• Oven thermometer - $20

Lowes:

• Chimney pipe, Supervent doublewalled stainless 6" x 3ft - $92.98 - ship to store for free
• Chimney cap, Supervent, stainless - $41.89 - ship to store for free

Let me know what you find.