Quantities for a barrel oven

[davidj]

Quantity questions...

For a barrel oven, how many firebricks do I need, approximately?
I'm thinking about 200.
I'm presuming 230 x 115 x 64 is the size to use?
About 14 per arch, four arches =56.
About 80 for the floor.
About 25 for back wall.
I think I'm going to add 10 thinner (51mm) bricks for the actual arch on the front of the main chamber...as its a little smaller than the main arches.
About 30 for the bottom of the walls and the transition.
Have I forgotten any, does this sound right?

Fireclay, how many 25 kg bags will I need?
I presume I need some for under the hearth bricks (optional I guess), and some for the fire mortar for the arches, back wall and front arch/transition.

Vermiculite, if I'm using it just over the main chamber in the insulating layer, is one 25kg / 100 litre bag enough?
On the subject of insulation, for under the hearth slab, I guess I have a choice of casting a 4" layer with vermiculite....or using thermalite blocks. The blocks are £1.02 each at my local Selco, so it seems like a cost effective solution.
Anyone got any experience of using them?

Thanks in advance.

[downunderdave]

You don't say how big your oven will be so advice on quantities is difficult. Regarding the insulation over the barrel arch, if only using vermiculite and no blanket then you will need a min of 100 mm. You can then work out the volume required. Depending on whether you are rendering a hard shell over it or building a dog kennel style will mean the difference between pouring it in loose or mixing with cement so it will go hard and you can render against it. If making a mix with water and cement don't go any richer than 10:1 brew or you'll reduce its insulating capacity too much. any leaner and the stuff becomes really hard to apply on a vertical surface. At a guess I'd say you'll need one bag of clay and two of vermiculite.

[davidj]

My thoughts were based on the Rado design (MTO) oven. This has a main barrel chamber 4 bricks long, so four arches joined together. Then the transition to a smaller arch and into the chimney, with the front entrance arch right at the front. 

I think I'll box the oven in and put a roof on. So loose vermiculite is probably the answer. Two bags will be needed based on that I guess.  

[oblertone]

I quite fancy a barrel build but most that I've seen built use 'separate' arches with no interlock between them. Purely from a structural perspective wouldn't interlocking arches be stronger ? I realise that this would require a longer (whole length) former but it would allow a half-brick overlap between courses which would be stronger.
I made my entry-arch former from sheets of 25mm expanded polystyrene pinned together with dowel and think this could be a quick and easy method of construction.

[downunderdave]

Feb 23, 2016 10:30:39 GMT oblertone said:

I quite fancy a barrel build but most that I've seen built use 'separate' arches with no interlock between them. Purely from a structural perspective wouldn't interlocking arches be stronger ? I realise that this would require a longer (whole length) former but it would allow a half-brick overlap between courses which would be stronger.
I made my entry-arch former from sheets of 25mm expanded polystyrene pinned together with dowel and think this could be a quick and easy method of construction.

I agree, for a barrel vault laying the arch bricks staggered or (on bond) is a stronger way to go. Barrel ovens and kilns should also have their end walls under the vault rather than sitting against the ends of the arches, otherwise when the vault expands it wants to push the end walls out.

[davidj]

My understanding is that laying the vault bricks "on bond" rather than as separate arches may lead to cracking along the centrelines of the bricks. This would be due to expansion and contraction of the vault, but with the bonding not allowing for linear movement. 

[davenott]

I built my barrel oven with 4 separate main arches. I've fired my oven up about 25 times, and so far no damage to any of the fire bricks.

I used tapered fire bricks, to give tight mortar joints. I used layers of stainless steel chicken wire wired together on the outside of the arch and backwall and then rendered over, before my oven insulation went on top, which I hope will act as a degree of bracing for intended expansion.

I read as many threads on this site about barrel ovens as I could before building mine, and there is some really useful information and builds.

I mocked my arches up, first in cardboard and then in the bricks without mortar, before doing the actual build.

If you look on the Kiln linings website, you can look at the kit they supply for barrel ovens and if you count the bricks, it will give you a rough idea of how many fire bricks are required. Their design can be improved upon, so I wouldn't copy it exactly, there are much better designs on this site, some of which I based mine on.