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Nev Grady 06-20-2009 12:56 AM

Cooking floor expansion joint
Arrived home yesterday after spending a few days away continuing the build of my WFO at our holiday home. As usual I logged on to FB Forum to see what the latest posts were and found one about an expansion joint for the cooking floor in situations where the dome rests on the insulating hearth and the cooking floor is laid inside it. According to the FB Pompeii Oven Plans this is the preferred method. Looking back on the forum today I can't find where the thread on this topic was posted! this expansion joint necessary?

I'm at an advanced stage with my build, and will be closing it up with the last few chains next week. I haven't allowed for cooking floor expansion, having laid the floor and built the dome tight up against it. Am I heading for disaster? If the floor expands outwards (the only way it can go!) then the dome will split if the expansion is great enough. Or will the dome expand too and accommodate the floor expansion in doing so?

Anyone experienced this problem before? If it is a problem the best for me would be to install the insulation, then after curing the oven, fire it up to as high a temperature as possible and see if any splits occur. Hopefully these could be repaired if they occur. As the insulation will be totally Insulfrax type material, which can be removed, it might not be too much of a problem.

I thought of this potential problem when planning the WFO but as the FB Pompeii Oven plans doesn't mention cooking floor expansion joints anywhere, I didn't leave one.

Rastys 06-20-2009 03:20 AM

Re: Cooking floor expansion joint
I built my dome with soldier bricks directly on the vermiculite cement insulation and then cutting the hearth bricks to fit the radiused wall. Have been using the oven for at least a year with ash filling any voids between the bricks and absolutely no movement.
I don't think that you have a worry in the world with your build.


Nev Grady 06-20-2009 03:30 AM

Re: Cooking floor expansion joint
That's how I've built mine with a first course of "soldiers". Thanks Rastys. That's very reassuring!

Rodneyf 06-20-2009 03:50 AM

Re: Cooking floor expansion joint
I hope you're right Rastys. I have cut my floor then built my soldier course around it with a layer of cardboard between the two. The theory is that the cardboard will burn away to leave ash and this will form the expansion joint.

dmun 06-20-2009 04:09 AM

Re: Cooking floor expansion joint
I don't think this is much of a problem. In theory, the bricks on the floor, and those on the dome are the same material, are about the same temperature, and will expand and contract at the same rate. If anything, since the floor bricks aren't mortared together, you would want to keep them pretty snuggly enclosed to keep them from wandering.

All these gaps get filled with wood ash in the event anyway.

Nev Grady 06-20-2009 08:56 AM

Re: Cooking floor expansion joint
Thanks for all for your replies! I was needlessly worrying then! I had a video running in my mind on first serious firing, or even during the curing process, of a loud crack and then the oven falling in on itself!!

david s 06-20-2009 07:12 PM

Re: Cooking floor expansion joint
I think the bigger problem is the uneven rise of temp and expansion between the top and the bottom of the dome. The only real way out of this problem is to keep the temp increase down to 100 C/Hr, but who would be bothering to do this ? Hell, we want to get it there as soon as we can so we can cook something.

Nev Grady 06-21-2009 12:51 AM

Re: Cooking floor expansion joint
When you think that this design of oven has been around for a few thousand years there can't be much wrong with the design and construction method.

Even so it would be interesting to hear from anyone who has actually experienced the problem of thermal expansion damage.

nitro69 06-22-2009 07:45 PM

Re: Cooking floor expansion joint
Is there any pro's or con's to having the dome rest on the insulation or the brick hearth ? Any suggestions ?

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