Clay oven building

[Feral007]

Just realised yours is on the ground. The one we are looking at is at waist height. Always a bonus since there are things on the ground that I don't want to meet up with, pizza or no pizza!

Not sure how often we'd be using the oven tho, since we are fire free all summer, and winter is a bit chilly.

[zazen999]

No, ours is waist height!

[Feral007]

Ok, I was looking at the photos and couldn't work it out. I was thinking you'd be bending down a lot to put things in and out

[zazen999]

If you look at post 2 you can see Lizzy walking behind it...

[Feral007]

What's underneath it? The base.

[zazen999]

It's essentially a massive raised sandpit. Built with sleepers for legs and concreted in. There will be another one built on the other half of the sandpit at a later date.

[zazen999]

Found a pic of the base only...

[zazen999]

New oven mostly built yesterday, just the final layer to go which will be built with one of our young students this week

Photos showing the lintel making in action as well as the oven with the sand removed.

[zazen999]

Oven done and lit. We let it burn for about half an hour and it did us toast.

[Mikey]

Lovely Zazen, I've been researching these for about 4 years now and for those looking at building your own here are a couple of pointers for you.

If you just intend cooking pizza then a cold base is fine if you want to also cook breads and slow roasts then it is advisable to insulate the base below the bricks using thermolite blocks this will keep the warmth for a lot longer.

The optimum oven space is 700mm round this is the space left after removing the sand, and there is a simple rule when working out the size of the oven aperture. The doorway should be roughly 67% of the height of the dome. Make sure when cutting the doorway out that you leave enough space to get an oven peel into approx 12-14 inches.

Just as Zaz's has done ideally you need two courses the first is clay and sand. The second includes straw. Both courses are best if they are approximately 4 inches thick giving you an overall oven dimension of 1100mm round. Take care when building as the courses tend to slip down giving you 6 to 7 inches at the bottom.

Cob ovens are porous so you need to make sure you keep the rain off, or you will find your oven will collapse after a shower. An awful waste of effort.

The best oven floor is fireclay bricks as these are designed for high temperature. There is a very good company in Bristol where you can get your firebricks relatively cheaply, pm me and I'll give you their details. Your clay oven will reach temperatures around 500 degrees celcius, most bricks engineered included aren't designed to cope with this and you will find you'll need to replace some after a year or so when they breakdown.

Lay the firebricks on a fine kiln dried sand base but don't fill the joins between the bricks or you'll have sand in your pizzas, the ash from the first few firings will soon fill the gaps.

You can fire up your oven after about a week with a small fire to help dry it out. If you are making one for long term use in the garden then its best to fire between the two courses as that way you can repair the gaps which will occur in the first course before applying the second outer layer, improving the insulation value of the oven.

I'm sure there will be other things that will come to mind, happy oven building.

[zazen999]

My 2 are already built and being used Mikey!

But we were using 63%; not sure where you got the 67% from...

Have you built one yourself at all?

[Mikey]

Its a 2/3rd rule zaz, I've built several with friends now but still to get around to the one at home as I have to extend the base with concrete lintels!! Its only 1100 square which doesn't leave room for the chimney I want to build off the front. Having trialled others I'm not keen on the discolouration you get above the oven door without a chimney.

As soon as my hands are fully mended I'll be extending the base ready. How many helpers did you get for your builds zaz? I'm hoping the friends I helped will return the favour in a month or two. Did you test your allotment clay for its natural sand level or was it a ball drop test afterwards?