Advice for Pizza oven

Hi, I'm new to the forums. I've done a search and didn't find an exact answer to my questions, so I decided to create this thread. I am planning to build a pizza oven and have a few questions. I have looked quite a few plans and this one seems intriguing. I won't make it portable though and will build a normal base, most likely out of concert blocks.

The base is made of firebrick, as usual, but the dome is made of a mixture of perlite and portland cement (5:1), with stainless steel needles for additional strength. Would portland cement be heat resistant enough for the dome of such an oven? I'm trying to keep the costs down, so if portland cement works, there is no real use in getting refractory cement.

The mixture for the dome also uses stainless steel needles. I live in Ireland and am not sure who to get them. However, I do have access to stainless steel wire, so I was considering cutting some up. It's normally used to make spinners. Could this work?

For the outer waterproof layer of the dome, I am planning on just using portland cement. It presumably rains a lot more here than in Florida, where the linked oven was built, so I want to make sure that it would be enough.

I don't have an exercise ball, but do have access to builders cement, so i will go back to the more traditional method of supporting the dome, while building it.

As for the firebrick, I managed to get my hands on some of storage heater blocks. I will use them instead.

Any other tips would definitely be welcome.

I wouldn't bother with the cement mixture--go with cob for the pizza oven--it will hold heat better and is more resistant to thermal cracking. Portland will deteriorate at low temperatures and you will end up with crumbly pieces of cement on your pizzas. You are also looking at a lower cost with no need for cement or the steel needles. You can use straw for tensile strength in the cob.

check out this build for inspiration http://www.theyearofmud.com/2009/09/12/outdoor-cob-pizza-oven/

No need for an exercise ball--find some sand and wet it down so that it holds a shape--think sand castles--then form it into a dome cover it with newspaper dipped in clay slip, then you can start putting a nice layer of cob over the whole thing. Once it is dried you pull the sand out from where the opening is for the door.

Google cob pizza oven and you will find a ton of good builds and many with instructions.

There's also the recently funded Kickstarter Paul did for the Rocket Oven:

https://permies.com/t/93740/Cooking-Rocket-Oven-microdoc



There's probably several more threads on this site about it, search for 'rocket oven' and take a look. It heats up faster and is portable, and there's a related thread link showing some of the nice decorations people have added to make it look more like art (which is doable with cob too).

Thanks for the tips/replies.

I live in a damp climate, the West of Ireland. Would that be a problem for the cob? It will certainly take longer to dry, but once it's dry, would it last?

You mentioned that Portland cement will deteriorate at cold temperatures, at about what temperatures will this start? Ireland has a mild climate and doesn't suffer from sever winters.

The rocket oven seems really interesting, but I assume that the cost would be higher than a pizza oven. I'll look into it some more though.

Cob works well in damp environments so no problem there. The cob will last if you put a protective coat of plaster over it, I'm sure you can find some lime to plaster with which would work well. Or if you are planning on building this under a roof then all the better.When I said cool temperatures would deteriorate the portland, I meant low temperatures in an oven environment--the normal fire temperature inside the stove will damage the cement.

A rocket oven needn't be expensive, you can buy plans for making one using a couple of 55 gallon steel barrels.  The plans Paul came up with for his Kickstarter last summer don't require welding - you do a lot of riveting to fasten the metal things together.  (I do think you need to find somebody who can weld for a nice set of shelves inside the oven, but honestly I rarely cook things on multiple shelves, so maybe you don't need shelves.)

I like my rocket oven because it heats up quickly and gets really hot.  A cob oven gets really hot, but it takes a LOT of wood to get it there.  It will then stay hot for a very long time.

I'll just back up what Daniel said about concrete/cement - it can NOT tolerate oven temperatures and will degrade.  Cob is a much better choice (sharp sand, clay, chopped straw) and just gets stronger with exposure to heat, because the clay will vitrify.

An earthen, or cob oven, will work fine, and it's on my long laundry list of construction projects. Unfortunately for me, it's low on the list, but it is there! If worried about precipitation, you could build a simple roof over it. That's my hope for my outdoor kitchen, when I finally get around to that project on the property... One of the simpler tutorials for how to make one, is Jon Townsend's. He's got such a pleasant manner that I go to his channel to watch a video or two whenever I feel down in the dumps.

Hi Nevenoe, I cooked using a hand built cob pizza oven in Kilkenny quite a bit 8 years ago.  It is still there being used and in perfect working order while exposed to all the rain we get.  The pizzas were delicious.

I've seen cob ovens used in Western Washington State (the wet side) and they all needed some sort of cover or roof over them if you want to keep the cob pristine.  A simple structure with four posts and a piece of roofing of some sort over it is all you need.  What little moisture that blows in from the side is negligible.  

If you don't mind that the cob weathers, then let it rain.  

Clay and sand are much more stable than portland cement (and any product that is constructed with portland cement like a concrete block).  While there is some expansion when a cob oven heats, and contraction when it cools, the straw in the cob is the rebar that holds it all together as well as the expansion joint that allows for a certain percentage of expansion and contraction.  Its such a simple technology, but it works tremendously well.

Do you have any sense for the percentage of clay in your soil?  The higher the clay content, the easier it'll be to make cob.  I'm not at all familiar with the soils in Ireland.

Best of luck with your project!

Thanks for all of the feedback. I will stick with a cob oven for now. However, I still need to find some clay, because there isn't any on the land where I will be building the oven. As soon as I figure it out, I should be able to start.

Does lime have to be replaced often? I've heard of it weathering too. A roof, or both, does seem like a safe option.

Nevenoe Guegan wrote:Thanks for all of the feedback. I will stick with a cob oven for now. However, I still need to find some clay, because there isn't any on the land where I will be building the oven. As soon as I figure it out, I should be able to start.

If you need to, potter's suppliers sell clay in a powdered form by the bag, even in Europe.

Penny Oakenleaf wrote:
If you need to, potter's suppliers sell clay in a powdered form by the bag, even in Europe.

That's good to know. About how much clay is used for a medium sized oven, e.g. 600 to 700 mm in diameter? Seeing as I won't be able to get if from the garden, I will have to know how much to get, wether I dig it somewhere else, or buy it.

Nevenoe Guegan wrote:

Penny Oakenleaf wrote:
If you need to, potter's suppliers sell clay in a powdered form by the bag, even in Europe.

That's good to know. About how much clay is used for a medium sized oven, e.g. 600 to 700 mm in diameter? Seeing as I won't be able to get if from the garden, I will have to know how much to get, wether I dig it somewhere else, or buy it.

I'm by no means an expert, I've got this project on my long list of to-dos. I have found this site helpful http://pinkbird.org/w/How_to_construct_a_pizza_oven_dome_out_of_cob

And some plans on the same site to peruse for research: http://pinkbird.org/w/Wood+fired+pizza+oven+building+plans/385

What I really like about cob ovens, is that you can let your creativity shine. This is perhaps my favorite of the bunch, and Li Ziqi demonstrates using empty wine bottles for insulation in the project.

For anyone thinking of building their own pizza oven, Paul's just posted a short video about building a rocket oven here.

There is also the new permies website: wood-oven.net that has info, plans and an instructional movie to make your own