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David Reekie 05-11-2009 02:37 PM

Dave's cast refractory oven
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Hi guys,

finally time to post up some pics and experiences of my oven.

To begin at the end, here's a pic of the oven as it is right now and a first pizza pic, both from last weekend. My pizza shaping skills need a lot of work! The beer in the first picture is Bath Ales Gem - highly recommended ;-)

David Reekie 05-11-2009 03:05 PM

Re: Dave's cast refractory oven
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To return to the beginning, I started planning around Christmas time, after finding this site, reading the full plans (thanks James!) and seeing lots of great ovens built by all you guys. We've got an established garden with a lot of hard landscaping already in place, and some quick measuing showed I couldn't fit even a 36" oven with standard Pompeii construction in the space I had available. You can see how squeezed in it is in the previous post - the back of it is right up against the boundary, and the front against an existing wall I didn't want to remove. So I'd have to go a bit smaller, and / or change the construction a bit.

I'd seen a few cast refractory domes, including dmun's masterpiece, and that got me thinking. I reckoned I could go thinner - say 50mm - with cast refractory and a slightly smaller dome - say 850mm / 33.5". Add 50mm / 2" of fibreblanket at the side and then 25mm / 1" stucco / render outer shell, and the whole thing would be 1100mm / 43" wide. With a single brick length entry arch and vent, It would be 1200mm / 47" deep.

That would fit the space and also provide enough cooking space to be just worthwhile.

It would also be much lighter than a standard Pompeii, so potentially much cheaper (less material to buy) and much quicker to heat up. It wouldn't be so good for retained heat cooking, but I'd try and insulate as well as I could and that was a trade off I'd have to make. If it doesn't heat in an hour I'm sure I'll use it much less than if it does, anyway.

Since it was going to be a much lighter dome then normal I could get away with much lighter construction of the base too. I didn't want to have to cast a concrete slab for the dome to sit on. at 1200mm square, I decided to use 4 600mm square standard concrete paving slabs. You can see hem in this pic, where I am starting to cast some of the perlcrete which will surround a central slab of 50mm board. (Getting impatient, and wanting o do somethiong while waiting for the board to arrive- I late ripped half of this out as if happens!)

Attachment 11833

(Anyone know why my pics are appearing full-screen in a separate window unlike everyone else's?)

David Reekie 05-11-2009 03:17 PM

Re: Dave's cast refractory oven
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The paving slabs were an ideal solution to not wanting to cast a slab. But even with a light dome I didn't want to push my luck and put too much weight onto the unsupported middle of them. That's why the walls forming the stand are a bit in from the edges of the slabs. If you look down from the top and draw out the dome on tops of the slabs and the outline of the walls holding the slab up, most of the dome is sitting directly on top of the walls, with the slabs sandwiched inbetween. They certainly won't break in pure compression, so this should be plenty strong enough. In retrospect I'm sure it's overkill - I bet I could have had the walls at the edges.

Moving the walls inwards on an already small stand was staring to hugely reduce my wood storage space. Not good. So I went for standard 100mm blocks, mortared into a standard wall, rather then the 200mm blocks which can be dry stacked and the cores filled. Slower then dry stacking, but no real choice.

I still needed something to hold up the middle of the slabs, and the front of the slabs. Well, I'd avoided casting slab so I didn't want to start casting anything reinforced now, so standard off the shelf pre-stressed concrete lintels did the job.

Here are a couple of shots of the inside of the stand. A real mix of blocks - mostly odds and ends I had lying around. Some cut to size - easy with a normal saw, if they are lightweight insulating blocks.

David Reekie 05-11-2009 03:24 PM

Re: Dave's cast refractory oven
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Since the pictures are gradually getting lower and lower (and in keeping with starting at the end of the story!) - here are the foundations. One of the advantages of a lightweight build is that you can go very lightweight here too. I went for a ring foundation rather than a full slab with a cut out in the front (so a 'C' shpe if you like). In this pic I've cast a thin layer of concrete I happened to have spare at some stage in the middle, just to act as a floor - but it's only 25mm thick. The foundations are about a 200mm square section at the edges. My so-called soil is basically clay anyway, so very little digging was needed to reach a solid base.

You can also see an initial ring of bricks followed by a damp-proof course before the block work starts - I thought I should add some extra insurance against the damp, since I'm in the UK ;-)

David Reekie 05-11-2009 03:41 PM

Re: Dave's cast refractory oven
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Stand done, time for the dome. A 50mm layer of insulating board went on first, with perlcrete cast round it up to the edge of the slab.

I had a few firebricks - a very generous gift by aureloe - thanks aureole! There were just enough for the cooking floor - but I also had some refractory concrete courtesy of aureole too. Since I was going to be making the dome 50 mm thick, and general experience from reading on this forum is that the floor is slower to heat than the dome, I decided not to use the bricks. I decided to experiment and try the refractory concrete for the floor too. I used a 50mm wide strip of hardboard to form he shape: bent into a circle, with a sticky out bit for under the entry arch. Casting the floor was dead easy. So far it's seeming ok - a single crack but that's it.

Then use some of the clay soil I'd dug out for the foundations to make a former, cover it with newspaper to make it easy to remove, and plaster on the concrete for the dome. Much easier than I thought - I was dreading this bit. I bought some extra concrete and it turned out to contain a few stainless needles, which I was very pleased to see.

Attachment 11837

You can see I'd made a start on the vent / chimney arch by now. Two reasons - impatience :) but also cos I wanted to be able to tie the dome to the chimney. With the chimney arch only 1 brick deep I was slightly worried about stability - so you can see I've got metal bars tying it into the dome. These needed to be in place as the dome was cast, and it was easier to locate them after starting the chimney arch.

The following pic shows them even better - the lower ones already tied in to the bricks, upper ones waiting for the bricks to meet them.

Attachment 11838

You can also see reinforcing in the bricks. They were standard 3-hole engineering bricks: to give the arch strength I filled all the holes with concrete as I was building, and added reinforcing steel in the centre hole.

David Reekie 05-11-2009 03:48 PM

Re: Dave's cast refractory oven
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Digging out the clay was a bit slow but very satisfying - seeing the dome where all the action would take place fully revealed. And not collapsing !

Onwards with the chimney arch / vent. More engineering bricks. Lot of trimming of the bricks with an angle grinder, before mortaring them in place, to create a vent and hole for the bottom of the chimney.

As you can see, it was dark when I took those. That's why I'm missing a lot of shots from earlier in the build too - I did it in the evenings and normally finished in the pitch black. Impatient, me? - never ;-)

The wooden former for the arch is two pieces of board: with the trimmed bricks I needed a support at the front and the rear of each, not just in the middle.

David Reekie 05-11-2009 03:54 PM

Re: Dave's cast refractory oven
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First fire !!!! Woo-hoo !!!!

In the dark. Again. Blue / green plastic sheeting covered the oven between building sessions.

You can still see the remains of the newspaper from the dome casting! It will burn off when it gets hot enough. You can also see the underside of the vent.

Les 05-11-2009 03:55 PM

Re: Dave's cast refractory oven
David, are you using core bricks for the vent arch? They are not made of refractory material are they?


David Reekie 05-11-2009 04:00 PM

Re: Dave's cast refractory oven
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Home straight now. Maybe.

Not enough pics of this bit, but very standard layers of ceramic blanket (50mm of the sides, 75mm on the top) followed by chicken wire and stucco / render: 2 layers, for c. 25-30 mm total.

All the concrete and lime (I used lime render on the outside of the stand) also came as left overs from aurole - thanks again!

Everything for the entire project was hand mixed in a bucket. By me on my own. Made for some slightly frantic periods when doing the inner and outer domes: needing a next bucket load quickly before the stuff already applied lost its workability. Top tip - a hoe makes an excellent stucco / render mixer ;-)

David Reekie 05-11-2009 04:01 PM

Re: Dave's cast refractory oven
Les - yes I am, and no they are not. I have my fingers firmly crossed !

Seriously, they ought to be OK for chimneys, which is basically what this is. I hope.

I'll report back if they fail :-(

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