New oven build in odd shaped area

[Mickey-t]

Hello everyone,

Long time no write from me. I started a thread around 8 years ago about building a clay oven, and I received some excellent advise from you good folk. I have since built two of these ovens and been happy with the results.

We recently moved house (again) and I am currently looking at building my 3rd oven, and this time around I would like to go brick. We have a space in our outdoor area that would allow me to build a Pompeii style oven that would have an internal diameter of 28". This is the only place I can build the oven, so was wondering whether it will be worth it, or if this would be too small. Failing that, is it possible/recommended to build the oven more oval rather than round, as I could go a little deeper than wider with it? I could probably make the depth 35" at its longest point.

Failing all else, I would build another clay oval oven. As I say I have been happy with both ovens, but this is our forever home and a more permanent brick oven sounds appealing.

Any help would be very gratefully received :-)

[UtahBeehiver]

David S of Aussie land builds smaller cast ovens. He swears by them, lower fuel consumption, faster heating times. Look at his thread.

[Mickey-t]

Thanks for that, I was hoping to get some opinions on going oval shaped rather than circular. Pros/cons? Has anybody built such an oven?

[david s]

If building a oval form in brick, it makes the use of an IT difficult. You could do it with two and use a straight section joining the two spherical ends or, probably easier to use a sand mould to place the bricks against. If casting the dome a sand mould would be the best way to do it.

[Gulf]

I've thought about David's first choice a lot. It would allow you to inspect and clean the brick joints. A sliding anchor point for the pivot of the IT would allow for one IT to place all the brick.

[david s]

I've thought about David's first choice a lot. It would allow you to inspect and clean the brick joints. A sliding anchor point for the pivot of the IT would allow for one IT to place all the brick.

That would work Joe, although it still wouldn't be a true oval. It would still be two hemispheres joined with a straight section in the middle. To create a true oval you'd need two fixed points with loops through which a cord is threaded with the ends tied together. This will give you a true ovoid form.

[Mickey-t]

Thanks fellas.

Yes David, I Was planning on building the bottom courses by eye and then building around a sand mold.

I am also considering a sand mold and then using castable cement/concrete mix (I wasn't aware that there was such a product)

The previous two ovens I built were oval shaped with a ball clay/sand/crusher dust mix with sisal rope strands mixed in as a binder. They worked great, and once again, I am faced with a similar shape and dimensions to work with. I just thought a brick oven would be a better more permanent feature, as we don't intend moving house again.

All opinions/advice is gratefully received :-)

[david s]

If you plan on using a castable mix there are a few options.

1. Get a dense castable refractory from a refractory supplier. This contains high temperature aggregates and burn away fibres to assist drying and reduce steam spalling. The cement component is calcium aluminate which is way more refractory than Portland cement. Unfortunately proprietary castables are way more expensive than you'd like.

2. Make up your own brew with calcium aluminate cement (Ciment fondue) and cracker dust around 3:1. This is the mix often used for lining chimneys. Not sure about it workability, you might need to add some clay to improve that. Also add some burn out fibres.

3. Make up your own castable using home brew (3:1:1:1) sand, lime Portland cement, clay. This is very cheap, but you need to add the burn out fibres. No guarantees about its longevity.

In all three cases you can enhance strength by adding stainless steel needles (melt extract fibres). The larger a casting is the more prone it is to cracking due to the uneven heating, although because of the form cracking is only cosmetic. Each of these castables is way stronger and should last better than cob.

[Mickey-t]

Thanks again for taking the time and effort to reply, it's much appreciated.

Well, I made the decision to go with the original clay one. I just didn't have the room to put in a decent sized Pompeii style oven. I have bought the materials today. I had already prepared under the floor, so today I laid the firebricks and row of skirts, so tomorrow, it's all on. Sand mound then mold the clay mix around it.

The last two ovens were built with clay pavers on the floor and skirts, so I am eager to see the difference with upgrading to proper fire bricks. The last two ovens cooked great, but the pizza base didn't crisp up, and was a tad "limp". I have been reliably informed that it was due to inferior clay pavers being used.

I will take a few photos along the way, and I shall try to post them up on a new build thread.

Once again, thanks for the help and suggestions :-)

[david s]

Have you insulated under the floor? One of the main reasons the base won't crisp up is that the floor is not hot enough. Lack of floor insulation is often the cause.

In my previous post I should have offered a 4th option for a castable mix, which is to add cement and or lime to the cob mix. This should produce a more durable mix although I've not tried tried it, so no guarantees.

[Mickey-t]

Yes I've got about 6" of Perlite/cement under the floor. I was advised to insulate under the floor by people on this forum when I originally built back in 2008. The plan I was following had crushed granite under the floor, which I was told in no uncertain terms NOT to do. :-)

I was talking to the (Italian) owner at the shop where I bought some supplies, and mentioned that I had used clay pavers on the floor, and that the pizza didn't crisp up. He told me to ditch the clay pavers and go firebrick. So, we shall see.

[Mickey-t]

The mix I am using is equal parts of ball clay, brickies sand and stone dust. Then 10% Portland cement and a good handful of fibres. It's been successful twice, so I'm sticking with it for a 3rd time . :-)