Fife barrel/vault oven build - the leaning tower of pizza!

[clanny]

Ok, fingers crossed I can make a better job of this post.

I've been collecting bits and bobs for a couple of years now and am finally getting a chance to make some progress. As I've picked up free bits, my design has had to change to accommodate the different sizes. I ended up with a mix of 100 and 140mm concrete blocks hence the "big and small" descriptors on my drawings. I eventually gave up and purchased a pack of new 140mm blocks for £25 and picked them up locally (two trips with about 1/2 ton each in my car).

I found a half pallet of (brand new) fire bricks for a power station furnace that came with 8 tubs of refractory cement. The bricks were in three sizes so my design has been worked round the size of the bricks.

Ill try to put this thread together in order and add in the info/drawings etc that I used to help me out. The drawings have evolved but I'll add them in so you can see the process. It might help others in their builds. Obviously, never having done anything like this before, the plans are only remotely reflected by what I've built!


So, here's some photos:

First the plans.



Rather than worry about how to shutter for a concrete oven base on top of three layers of blocks, I decided to make use of some 600x600 slabs I had lifted earlier.

Time to do some real work - foundations.





Mocking up to find the right height for the oven floor.


On with laying some blocks. I thought that bigger would be better, less joints for me to screw up, however, they're hard to move about and position on the mortar. With hindsight I'd use hollow blocks instead.




I cut another slab to fill the gaps.







Centreline marked up.

[clanny]

Now to put down the insulation for below the oven floor and walls. I had bought 3 x 600mm cel on blocks but I needed the insulation to be wider so heat wasn't lost from the walls so I bought thermalise blocks which have the same thermal insulation of 0.15.



Once again, the design has changed. Rather than cementing down the oven floor and building the oven walls up on top as I'd planned, I've been advised to build the oven walls up from the thermalite blocks and put the oven floor inide, not mortared down. This'll give some leeway for thermal expansion of the floor and hopefully reduce cracking.

[clanny]

Probably too much detail but here's the rest of the drawings I've done. Might be useful to someone.

[clanny]

Spent the day in the sunshine, on the oven again. Really couldn't get my head round making a form for the arch so just started putting bits of wood together until I came up with this.






Then i I started looking at extending the insulation for the base towards the rear of the oven. This will give me more room at the front to create the flue and landing area. 



 Tomorrow I'm hopefully going to make a form for the oven arches and then start putting the oven together with fire cement.

[oblertone]

With apologies to 'downunderdave' the attached is copied from another thread, but is relevant to yours; particularly in regard to the siting of your end walls.

A barrel oven presents some problems regarding inherent instability under thermal expansion. Because a hemispherical dome is self supporting it is not subject to the same problems. One of the problems is the expanding vault which has the tendency to push the end walls out. This problem is exacerbated by the difficulty of tying the end wall into the vault, they are therefore usually built just butting against each other. For these reasons the end walls are better built under rather than beside the vault. In kiln design where thermal expansion is greater and more of a problem the usual technique is to brace the structure with angle iron and threaded rod, especially if the end walls are not built under the vault. A much stronger vault is also obtained if the bricks are staggered rather than laid as separate arches. A third weakness with a barrel arch is the base of the vault where there is some side force. Often buttressing is used to counter this, although a semicircular vault is pretty self supporting. A flatter or larger diameter arch produces a larger side force and presents more problems. The Ancient Romans were mad on semicircular arches and they used them everywhere, but when it came to ovens and kilns they preferred the hemisphere. Not wanting to rain on your parade, but these are things you may want to consider.

[clanny]

Cheers for the heads up Oblertone. I wasnt planning to have the end wall under the arch but have redesigned so it is. This'll cause quite a bit of brick cutting which no doubt will be as inaccurate as it has been all the way through so I'm not sure how I'll seal that part of the oven. I've also left the side walls unmortared to the rear wall. This should allow the walls to move separately from the rear wall if they need.

I'm looking to get some angle iron to make a brace for the oven so it doesn't move too much under heating. If I can brace the oven, maybe I can go back to the original design.

Today's rookie mistake was realising that I'd made up the entrance arch form sized for the firebricks when I'd intended to use reclaimed paving bricks. Add this mistake to the growing list of dumbass moves including, cementing the walls down at 420mm wide when they should have been 590mm (not a clue why but fortunately I realised before the mortar had set), building the arch form for this 420mm gap (this took hours but I can use it for the entrance so not time wasted), cutting the celcon block 90 degrees out (measure twice, cut once - durr) causing extra cuts and wasted time. This week has definitely been a learning curve and the biggest thing I've learned is that I hate arches, or more specifically, arch forms.

[downunderdave]

If you've already built the oven I don't think it would be worth all the extra effort of deconstruction and rebuild of the end walls at this stage. But some steel bracing around the oven would be a prudent move. Generally the angle iron would sit against the end walls with the rod running parallel with the vault.
The advice re barrel oven design may be useful for others to consider.

[clanny]

Cheers for the help guys, very much appreciated.

Until this morning I just had the rear walls and soldier course (if you can describe one large brick and two small ones as soldiers) of side walls done. Today I picked up some angle iron and then set about with some last minute checks on the arch. Measured and dismantled it three times to get it perfect and then took it apart for cementing in place. I took account of the mortar and yet when it all went back together it was still out. :-(

Had to reshape the key brick into a genuine keystone shape by hand. Anyway, it's all put together now and I hope it holds. I cut some firebrick wedges to help fill the gaps so I could use fire cement. Man, did that make a mess! I tested the refractory cement previously and it seems that if you let it dry properly (heat helps), it sets good and hard and seems to be able to bridge bigger gaps. I don't have any fire clay to make home brew you see. Maybe I should get some as I'll need it for thermal mass media concrete for the outside. I'll go search for suppliers up here.

I'm hoping I can work out a way to use the angle iron to brace the outside of the oven but the difficulty is that the bracing will need to round all four walls. The only height I can do this at will be the level of the 63% transition lintel piece from the oven to the chimney chamber. This shouldn't be a bad thing though as it'll be handy to use as a support piece for the firebricks. I haven't got it totally clear in my head how it'll look but it'll come I hope.

[myke]

Hi liking your former looks well engineered i just used a bit of hardboard and a few scrap bits of timber and my arches are ok so carnt see you having problems with yours.
Good luck with the build

Myke

[clanny]

Testing the the arch former.

former for the front arch.


The first arch up with wedges and refractory cement.


Gaps filled with more refractory cement (plenty of cracks but it seems secure).


More 15degree wedges cut and a lidl gazebo to keep the rain off.

Template for the oven floor.

internal of the first arch.

oven floor down on a bed of fire clay/cement dry mix.



Second arch up. Again, plenty of cracking but it'll all be covered over with a layer of mortar (or should it be concrete?) so cracks will be filled. The wedges are keeping it structurally sound I hope. They'll also give some nice keying points for the next layer.

The next bit, which has me completely stumped at the moment is how to transition to the chimney area. Ive noticed previous builders have tapered the full oven height down to the magical 63% but would it make much difference if I just dropped vertically down to the 63% threshold? I was thinking it would be much easier to simply put some angle iron across the entrance and put a large firebrick slab on top of that.


 And lastly, how to supply the builder with enough volume of rock n roll whilst he's toiling away?

Solved.

[oblertone]

Excellent progress; fwiw my build was a dome but I used angle iron to support the entry arch and it works just fine.

[downunderdave]

The sideways thrust for a flatter arch is far greater than that of a semicircular one. This means that some bracing or buttressing of your side walls becomes more important. The heat cycling and resulting expansion and contraction will exacerbate any structural weakness over time.

[stevo]

This is how i made mine - maybe over engineered but it's solid...

[clanny]

I've been making some more progress so thought it was time to update my thread. its not finished yet but I'm well onto the finishing straight.

After your advice, I braced up the sides and I managed to blag some huge thermalite blocks with which I built the side wall.

[clanny]

Clay and cement dry mix to bed the oven floor in.












Test fitting the oven entrance /landing area.

I
Building the base for the entrance arch, landing area.


Built a lintel about 63% of the height of the oven peak height. Firebrick resting on thick angle iron.


Side bracing to combat transverse forces as described above.




I used thermalite blocks to insulate and brace the sidewalks. Cut to fit the contours as best I could. Two jobs with one material.
















A temperature/expansion break between the oven floor and the landing area.


Gap filled with thermalite offcuts.


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