#1  
Old 04-06-2008, 04:17 AM
Laborer
 
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Location: Australia
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Default Pompei Oven and Cracks

Hiya all,

I have read through quite a few construction threads, steves from Austin and Georges threads stand out to me. I have a question with regards to the cracks that have formed in these oven constructions.

It is comming to WInter here in Australia, our temperatures dont really get as cold as Washington State and I dont think it gets as cold as austin either but I dont know how cold it was during Steves construction.

I was thinking about laying the slab and hearth and doing the dome construction in Mid spring ( October) so leaving the slab for the next 6 months. I dont know if I will be able to do that cause I dont really want an ugly slab in my back yard and would wantto build the oven.

Anways I have gotten of track as I seem to do alot my question is

Is there a down side to me building the dome, chimney, doing the insulation and putting together the single brick wall for the casing and hip roof and then leaving the curing of the oven until mid september (6 months).

Now I know what some you you are going to say, will I be able to resist the temptation of lighting it for that long.Well that remains to be seen.

Any ideas as to why leaving the oven for 6 months before doing the initial lighting and subsequent lightings for curing would be a bad idea??


Thanks
Imran
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  #2  
Old 04-06-2008, 07:52 AM
dmun's Avatar
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Default Re: Pompei Oven and Cracks

That's exactly what I did: let the completed dome sit over the winter under a temporary roof. It worked fine. If any thing, letting your mortar cure for months is a good thing.
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  #3  
Old 04-06-2008, 04:20 PM
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Default Re: Pompei Oven and Cracks

Did you get any cracks or did it cure properly. I mean I know there will be some cracks nothing is ever perfect but from trhe first burn is probably not the best thing.

Imran
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  #4  
Old 04-06-2008, 04:51 PM
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Default Re: Pompei Oven and Cracks

Yes, I did the full seven day increasing size fire cure. My cracks developed over the first few months of operation, and I may have a few more than average because of the thinness of the dome, and the stress of a two story masonry chimney liner bearing down on it.

If a few hairline cracks are going to bother you, you should spring for the modular ovens, which never crack.
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  #5  
Old 04-06-2008, 05:21 PM
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Default Re: Pompei Oven and Cracks

I agree. Should not be a problem waiting 6 months to cure. What's your rational? Worried about cracks? While there have been many discussions about the length of time that it takes cement products to gain full strength (75 years or more) I think 30 days would be an adequate wait period to assure everything's pretty well cured. Though I didn't research it, I'm pretty sure that a graph of the strength of concrete vs. time would show a pretty sharp rise in strength over the first 30 or so days then flatten out significantly after that period. Who knows? I'm sure you can find the information on the internet pretty easily.

I assume you don't have much rain there during your summer. If that is the case, you probably don't need to worry about covering it too well.
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Old 04-07-2008, 02:10 AM
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Default Re: Pompei Oven and Cracks

Quote:
Originally Posted by gjbingham View Post
I agree. Should not be a problem waiting 6 months to cure. What's your rational? Worried about cracks? While there have been many discussions about the length of time that it takes cement products to gain full strength (75 years or more) I think 30 days would be an adequate wait period to assure everything's pretty well cured. Though I didn't research it, I'm pretty sure that a graph of the strength of concrete vs. time would show a pretty sharp rise in strength over the first 30 or so days then flatten out significantly after that period. Who knows? I'm sure you can find the information on the internet pretty easily.

I assume you don't have much rain there during your summer. If that is the case, you probably don't need to worry about covering it too well.
My rational is that winter is comming and its not really a time I do BBQ or any form of outdoor cooking so it would be ideal to leaveit sitting for as long as I can.Also I am a little worried about tempreature shock of ligthing hot fires and then having cold winter nights cool it down to fast whereas in spring/summer I can light it and the temp isnt that cold.

I have been sufferingf rom depression for the past 3 years and I know if I dont build it now then it will only ever be 1/2done. My wife is saying dont wait till September to build it, why notbuild it during the colder months when it isnt to humid or hot.

Thanks

Imran
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  #7  
Old 04-08-2008, 04:54 PM
Peasant
 
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Default Re: Pompei Oven and Cracks

I've been reading about cracking domes and have been wondering how porous cement is and whether any of this cracking might be the result of air expansion of air pockets between bricks that have been mortared over. Is the mortar sufficiently porous to allow the air to escape from such pockets as it heats during firing? If not, might that not be the source of some of these strange cracks that have been appearing?

I suppose one way to test the theory is to monitor how the cracks appear. If they appear as the oven heats up, but then close to some extent as the pressure equalises, air pockets might be the cause.

Of course, I cannot test the theory myself coz I am still in the planning stages. Would be nice to know whether small air pockets between bricks are dangerous to the dome, however, before I start building.

Cheers
Paul
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Old 04-08-2008, 05:53 PM
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Default Re: Pompei Oven and Cracks

Firebricks are quite porous. Put one in a bucket of water, it bubbles like crazy. When trapped air (or water vapor) expands with heat, it vents right out the bare face of the fire brick.

Mostly the cracking problem is uneven heating. The inside is hot, the outside cooler. The back of the oven is hottest, the mouth is not so hot. Every material except ice expands with heat, and the variable expansion in a rigid system like a brick oven imparts tremendous stress, and something has to give.

Precast modular ovens are inherently stronger because there are only a few parts, instead of 150.
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  #9  
Old 04-08-2008, 07:31 PM
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Default Re: Pompei Oven and Cracks

Good to know if/when I ever get round to starting my project
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  #10  
Old 04-09-2008, 01:33 AM
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Default Re: Pompei Oven and Cracks

Thanks for the info if it doesnt really matter then I will try and start soon.

You guys are great,we are blessed to have such a great forum with such great people who are willing to impart their knowledge.

Thanks for the help guys.Will start posting pics once I start the project.

Imran
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