Lattice design for cob oven support

[vrdiver]

I'm hoping some more experienced Fools can advise me on whether the following design is practical.

I want to build a wood fired pizza oven, using cob. The plinth needs to be about a meter high, so my idea is to arrange 5 breezeblocks (440x214x100mm) in an "open" pentagon (i.e. they will not be touching each other, but have a gap of about 16cm between their nearest corners). The next layer is placed on top with a rotation of 36 degrees , and the third layer with another 36 degrees (so odd layers align with odd and even with even).

5 layers with some mortar gives me just over a meter height, which is then covered with a sturdy* support, and the cob oven built on top. The total weight of the oven will be about 600kg.

The question is whether or not the open lattice breezeblock will be OK for this load?

VRD


*I haven't decided on the base yet - could be wood, metal or concrete.

[redsturgeon]

Given that these blocks are usually laid in a single long line to perhaps 2 metres high and can support the weight of an upper floor and roof then I guess being laid in an inherently stronger form they should have no problem. Why the open lattice structure though? Isn't that inviting small creatures to make their home inside the new warm and cosy igloo?

I would be slightly worried about the wooden deck on top, given the nature of the temperatures involved in a wood fired oven, even though I assume a thick layer of cob on top of it will provide good insulation.


Is this the sort of thing you are doing?

http://thecobovenproject.blogspot.co.uk/

John

[vrdiver]

Thanks John,

Yes, that's pretty much what I'm attempting. By using the open lattice I get the foundation dimensions I want. The open lattice is me being lazy (not cutting breeze blocks to size) and a cheapskate (not buying any more than I have to!) and the gaps will be filled with cob, so small critters shouldn't take up home inside. The base, if wood, will have 8 - 10 inches of cob and insulation between it and the firebricks. Even so, I think I'm going to avoid wood in favour of a metal or concrete plinth, as it just doesn't feel right to use flammable materials to build an oven with

VRD

[MyNameIsUrl]

5 layers with some mortar gives me just over a meter height, which is then covered with a sturdy* support, and the cob oven built on top. The total weight of the oven will be about 600kg.

The question is whether or not the open lattice breezeblock will be OK for this load?

I've no doubt the structure will support the load when the mortar is set hard, but you have relatively little overlap of the blocks and will have to build up the layers over a few days, or you may find the weight of the upper layers will squeeze out mortar from the lower layers if you try to build it all at once.

[vrdiver]

you may find the weight of the upper layers will squeeze out mortar from the lower layers if you try to build it all at once.

Yes! I've read a few accounts where amateur brickies are struggling to keep the mortar between levels level, and without the experience of the professionals have had to wait between layers. The pro brickies appear to have learnt how to compensate for this, or figured a different mortar mix, but for my purposes a layer a day is fine - I can spend the rest of the day stomping on clay, sand and sometimes straw....

It's also good to have an excuse when the wife asks why I'm drinking tea again

VRD

[redsturgeon]

you may find the weight of the upper layers will squeeze out mortar from the lower layers if you try to build it all at once.

Yes! I've read a few accounts where amateur brickies are struggling to keep the mortar between levels level, and without the experience of the professionals have had to wait between layers. The pro brickies appear to have learnt how to compensate for this, or figured a different mortar mix, but for my purposes a layer a day is fine - I can spend the rest of the day stomping on clay, sand and sometimes straw....

It's also good to have an excuse when the wife asks why I'm drinking tea again

VRD

Tea! This is a job for beer!

John