Vermiculite pizza oven cracked

[lilla napoli]

Hey. I've built a pizza oven with vermiculite and cement last summer. The oven has been very good, making excellent pizza. Now to the issue, the oven has cracked on different places so that my chimney went through the hole and lays on the pizza oven floor. It has also beenn exposed to winter weather and the mix is coming loose. Do you think I can get it patched with a new batch of fire clay and vermiculite?

I've had this thoughts of making a new and more sustainable pizza oven of fire bricks instead in a barrel vault shape. I've calculated that I need around 100 bricks, the bricks I've found is each 3,5 kg which is 7,7 pounds. My construction is though made out of wood. Do you think my wood construction can hold around 350 kg, bare in mind that I've already have a concrete bas on top of the construction as an isolation. Or do you think i need to build a new foundation/construction of bricks that can hold all that weight? Sorry for my English, it's my third language.

thnx

[david s]

I'm not surprised that your oven has failed if the mix you used was just normal portland cement and vermiculite. Although the mix is a pretty good insulator if fired when wet will result in steam creating severe cracking. In addition normal portland cement does not cope well with temperatures exceeding 300C and degradation occurs. As well as these two problems a mix of vermiculite and cement results in a weak cast with little thermal mass, both undesirable characteristics for a wood fired oven.

I'd suggest you tear down and start again presuming your concrete base is still structurally sound. Make sure you insulate between the concrete base and the cooking floor. There are lots of well documented builds using either brick or cast materials on this site.


Why do you want to build a barrel fault? It has its advantages, but they are heavily outweighed by its disadvantages IMO. A lot of folk decide to build a barrel vault oven because they think it will be easier to construct than a hemispherical dome. Unfortunately they do not take into consideration the fact that a barrel arch that does not have support for the side walls is not as inherently stable as a hemisphere. This fact coupled with the thermal expansion and contraction every time the oven is fired, leads to stress an, weakens in the structure and cracking. The two methods of counteracting this problem are either buttressing of the side walls or steel bracing or even both. In addition, for ease of construction some folk build the end walls against the vault. Not only do the vertically aligned joint between the walls and the vault create a weak point the expanding vault has a tendency to push the end walls out. They need to be built under the vault and tied into the corners to prevent this problem. The buttressing and bracing also lead to other problems like corrosion and heat sink effect. By contrast the hemisphere is a far more stable structure and does not require either bracing or buttressing. It is for these reasons that it is the preferred design for thousands of years.
However if you have your heart set on a barrel arch, by all means research it well first and follow a successful design.

[lilla napoli]

Hey. Thanks for the answer. I do have an insulation between my concrete base and the oven floor. The insulation is made of refractory concrete and vermiculite, same for the dome, forgot to mention that. So the insulation is not the problem, rather that the oven cracked after couple of months in use and the opening of the oven was constructed weak. I've had plans earlier to put an insulation blanket on top of the oven for extra protection. So you think it's better to start over again and do it properly than to try to fix the cracks?

On why I was thinking of doing a barrel vault shaped oven is because it seemed easier to do it with a form than a dome. Do u have any thoughts on using wood construction as a base for eventual brick pizza oven? Or will it be to heavy?

[david s]

If you still have your heart set on. Barrel oven make sure you address the side wallweakness problem by either buttressing or bracing and build the end walls under the vault. A lightweight wooden form can be built, but you must have wedges under it that can be removed so it will drop and make removal easier.it is also better for the arch bricks to be staggered, rather than a series of separate arches.