Barrel/Vault Build in AZ

[Tat2Neil]

Some good info here, much appreciated David. Although, vermiculite is much better at water retention than perlite being as its puffed volcanic glass.

I’m confused as to what you mean by “and I suspect this is what happened in your case”.. my oven is still drying out on my mold, and is in one piece. And no, I do not have any plans to insulate below my fire brick floor. I know that is a very good thing to do, but again this is a total bare bones, budget build, In a confined space. I’m not trying to hold temps for days, or even hours on end, I just want to be able to cook a few pizzas for my family.
I’m simply doing what I can with what I got.

I’ve read through literally a dozen builds using the same references/formulas I used(except they use a medicine ball where I made my own mold), some from years ago, and none of which have come back with an update to talk about how their oven came crumbling down all over there pizza. Likewise if someone had it happen to them you would think I would find more info on it, but I can’t.

So I’m going to keep plugging away, and i’ll Let you guys know how it goes when I’m done.

[david s]

Sorry Neil, the reference to the crumbling perlcrete led me to believe that youd already started fires. Just be careful to do this slowly. If you see any visible steam, back off youre going at it too hard and risk damage. I think you will still have trouble attaining pizza temperature on the floor and maintaining it without under floor insulation. But maybe you can find that out for yourself and retro fit the insulation at a later date perhaps. Regarding the water retention of perlite and vermiculite, i’ve noticed no difference and have been using both for ten years. There is a product that’s unavailable to me which is silicon coated perlite which does not absorb much water. Both vermiculite and perlite are silica based exfoliated materials that are generally interchangeable. Hope this helps, we’re always interested in those builds that break some rules and out of the square. Good luck and keep us posted.

[Tat2Neil]

Despite the concistant cynicism from all the lovely ppl at Forno Bravo... I’m staying wildly optimistic about my little build.

I got the ‘shell coat’ of homemade refractory cement inside and out after I covered it entirely with chicken wire. Then had to have a couple friends help me hoist it up onto my base.

And David, thank you for bringing the under floor insulation to my attention. Although there’s probably more insightful and constructive ways to go about suggesting it, your comment did make me re-research floor insulation benefits and I modified my base design to include a 2in perlcrete insulation brick I made to install my fire brick over. So maybe if by some voodoo magic my oven does not come crumbling down when I go to light a fire, at least my floor will be able to retain heat a little better.

I know you’re all anxious for me to fire this thing up and start having perlite and stainless needles come raining down all over my pizza, but for now I’m gonna give it at least a month of curing/drying out before starting my break in fires. I’ve seen a few examples of brick builds on YouTube where you can see big cracks in the finished piece from rushing the curing process, going to do my best to avoid that.

Since we’ve already established your guys position on these particular types of ovens, I respectfully ask that at this point since I’m obviously not abandoning the idea, that you keep the negative comments to yourself. If anything, let this serve as a reference tool as ‘what not to do’ haha, I’ve already seen some of you linking to my build basically saying just that. But, do understand I am doing everything in my ability to prove you wrong.

[david s]

Neil,
far from being negative we have only provided our advice based on knowledge and experienced gained and a desire to freely provide advice that could be helpful. We love to see different innovative methods and for them to be shared. We wish you well, please keep posting.

Dave

[UtahBeehiver]

I am not sure where you are coming from on negative comments, as Dave mentioned, as members of this forum, our goal is to guide new builders to have successful builds. If letting you know potential construction pitfalls is perceived as negative comments then you are taking our advice incorrectly.

[Tat2Neil]

Perhaps you’re correct, I may have been a bit sensitive, assuming I was doing something innovative only to be told multiple times over I was setting myself up for failure. But I was committed and halfway finished before I had made my first post. Regardless I’m still searching for some first hand accounts of perlcrete or vermcrete oven failure. If you guys are familiar with some please send them my way.
I’ve seen many videos of these types of ovens functioning properly on YouTube. Not to mention my first experience with a homemade pizza oven was a small perlcrete oven that wasn’t even sealed and I could see the needles exposed all over, and despite it being 1-2yrs old and dozens of pizza nights later, I didn’t get anything on my pizza other than the toppings I put there, and it tasted awesome.
So I am legitimately curious as to when/where these structural failure are presumed to occur.

[wotavidone]

There won't be a failure as such. The dome will be more delicate than one made of dense castable but as long as you don't physically knock it around it should stand up. However, you did say your wife likes baking bread. Bread ovens usually have much more thermal mass than pizza ovens, This is where your oven may disappoint.

[david s]

Neil, i’ve had some experience designing a lightweight castable for a kiln I built several years ago. Because I want to use the kiln to reach stoneware temps (1200 C +) perlite and vermiculite are out because they’re only good for around 1100C. I did experiment with a few things including rice and sawdust, designed to burn out leaving air pockets, but they were both unsuccessful and I settled on crushed insulating firebrick. The resulting castings whilst being low in thermal mass and therefore creating a more efficient use of fuel as well as faster heat up are significantly weakened. Actually most kilns today have hot face ceramic fibre walls and roof in an effort to make them more fuel efficient. Care must be taken as with any kiln to make sure the walls and roof are not damaged during loading and unloading. The thermal mass during and after a firing is achieved by the mass of the wares and kiln furniture contained in the kiln. Whilst you are not building a kiln the principles remain the same. You may be interested in it’s build, here.
https://community.fornobravo.com/for...kiln#post14564

[Tat2Neil]

There won't be a failure as such. The dome will be more delicate than one made of dense castable but as long as you don't physically knock it around it should stand up. However, you did say your wife likes baking bread. Bread ovens usually have much more thermal mass than pizza ovens, This is where your oven may disappoint.

Thanks for responding, what takes the most abuse inside an oven? I don’t think i’ll be banging the brush into the walls much, or is it from adding wood?
Since I am lacking thermal mass, I know it probably won’t hold interior temps for long after the fire stops burning, which is okay, that wasn’t a goal when I initially decided to build. That being said, I am definitely going to attempt to do some bread since we only make 1-3 loaves at a time anyway, I may be able to hit a sweet spot during cool down and be able to crank out a couple.

[Tat2Neil]

Neil, i’ve had some experience designing a lightweight castable for a kiln I built several years ago. Because I want to use the kiln to reach stoneware temps (1200 C +) perlite and vermiculite are out because they’re only good for around 1100C. I did experiment with a few things including rice and sawdust, designed to burn out leaving air pockets, but they were both unsuccessful and I settled on crushed insulating firebrick. The resulting castings whilst being low in thermal mass and therefore creating a more efficient use of fuel as well as faster heat up are significantly weakened. Actually most kilns today have hot face ceramic fibre walls and roof in an effort to make them more fuel efficient. Care must be taken as with any kiln to make sure the walls and roof are not damaged during loading and unloading. The thermal mass during and after a firing is achieved by the mass of the wares and kiln furniture contained in the kiln. Whilst you are not building a kiln the principles remain the same. You may be interested in it’s build, here.
https://community.fornobravo.com/for...kiln#post14564

Very interesting read (and sweet kiln), I never would have thought about the use of saw dust or rice, despite it not performing properly the idea is intriguing. I definitely won’t be attempting to reach temps anywhere near 1100C in my oven, unless I’m attempting to vaporize my pizza ha!

[wotavidone]

Thanks for responding, what takes the most abuse inside an oven? I don’t think i’ll be banging the brush into the walls much, or is it from adding wood?
Since I am lacking thermal mass, I know it probably won’t hold interior temps for long after the fire stops burning, which is okay, that wasn’t a goal when I initially decided to build. That being said, I am definitely going to attempt to do some bread since we only make 1-3 loafs at a time anyway, I may be able to hit a sweet spot during cool down and be able to crank out a couple.

Two things come to mind with regard to knocking the oven around: be careful about throwing logs of wood in, and be careful with metal peels. I tend to use the peel for pulling out the ash, and it's easy to run the edge into the wall at the point where it adjoins the floor. And peels can end up remarkably sharp! Something to do with being slid over the fire brick floor at a very shallow angle.
Yes, you should be able to get a sweet spot as the oven cools where you can bake a couple of loaves. Time will tell.

[Gulf]

Placing a few live coals back in the oven could extend bake time while baking bread in a cloche. That should work for roasts, also. I don't have a stoneware cloche, but my cast iron dutch ovens and graniteware roasting pans work very well.

[Tat2Neil]

Well after spending a bit more time searching through the forum I definitely stuck my build thread in the wrong spot, that’s what I get for being gung-ho! Anyway, wanted to give everyone an update.

went through my curing firings, over 4 days, each fire increasingly hotter, tried to keep them all burning for 5+ hours. Everything went smooth. I had a small crack that I had accidentally created earlier when trying to move this beast by one of the weakest points, the flue opening... stupid move on my part, and my quick patch didn’t hold up and flaked off during one of the hotter fires, then I took a wire brush and scraped off anything loose, aside from the patch I made the rest was solid.

Then came the first pizza, and I must say, it was pretty darn tasty! I know they are definitely going to get better, especially when I have a better hardwood fuel source, the wood I had lying around is old, super dry, and burns up way to quick. And I must have not cured it as completely as I had thought (even though on my last firing day I had the whole outer surface of the dome reaching 230F, and there were no cracks, no steam). Because when I walked out to put my pizza in, there was a decent sized crack that appeared at the base by the entrance (see photo, behind the pizza). It really bummed me out at first, but then I realized that it won’t effect how it cooks pizza, and the main dome didn’t crack, which I feel is more important. And my interior dome looks exactly as it did when I finished it, other than now it has a layer of soot on it now. Pizza cooked in a little over a minute.

I finally got my nice pizza peel and after a another pizza night or 2 I’m going to render the outside of my oven and call it a day. I’ll come back and update in a couple months and we’ll see how it’s holding up, but I think it’s going to be just fine!

I did the math and in a perfect world where you only bought exactly what you needed, this oven would cost $275. I probably spent a little over $350 because of building my mold and buying excess stuff, and it took me about 3 weeks to complete.

Thanks again to all those of you who offered advice and pointers, without this forum I wouldn’t have insulated my floor and may have been very dissatisfied if it created too much of a heat sink. Thankfully I’ll never know haha! Cheers!

-Neil