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  #11  
Old 09-04-2009, 10:31 PM
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Default Re: Colorado oven

Great job Mark! I think a 42" dome that's 19" in the middle is perfection. Your jig you made to form the elipse to get you there is a great idea. I love the location of your oven in the trees too. Your vent transition looks good and I assume you're installing an 8" duratech since you've got the anchor plate in. With your cast transition and deep landing, it should draw smoke very well. Can't wait to see the finished oven.
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  #12  
Old 09-07-2009, 02:20 PM
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Default Re: Colorado oven

Nice Job for sure! I like the cast transistion - after making mine - I swore if I ever had to do it again I would cast it.

I was tasting pizza when I got to that stage, I bet you can't wait! Take it low and slow on the curing.

Christo
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  #13  
Old 09-07-2009, 04:02 PM
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Default Re: Colorado oven

I appreciate all the comments.

So, far I am resisting the urge to rush things at this point--although your comment, Christo, about your cooking pizza at this stage didn't help . I really want to get the curing thing done right. The curing protocol on this site doesn't make a lot of sense to me. Neither does the resignation that a cracked dome is a normal outcome. Perhaps I am being too naive, but I'd like to think I can avoid a crack if I do the curing correctly.

I have a number of problems with the recommending curing schedule. I have no experience with this--I am just thinking through the physics of it. I may be completely off, but here is my take. I think the first couple of days of lighting a couple of sticks of wood and then letting the oven cool immediately is doing virtually nothing when you consider the energy input in relation to the large thermal mass of the oven. I think the object should be drive out all of the moisture before the oven is taken over a couple of hundred degrees F. Perhaps that is not realistic in practice, but the recommended curing schedule can't do this.

I see two potential problems. First, the formation of steam could damage the structure. Second is the temperature differential that would exist in an oven mass heated above the boiling point of water with water still present. For instance, dry areas of the oven could heat up to many hundred degrees F while areas with retained moisture could not exceed the boiling point of water. That could create significant thermal stresses to the structure.

I think the recommended protocol is sound in intent, but falls short in actual practice. But, I am saying that as someone who has yet to cure his own oven, so take it for what it's worth.

This is the approach I'm taking (until I change my mind). I am holding the air temperature inside the oven at 190 F until the temperature of the outside of the dome under the insulation approaches the oven air temperature. That should indicate that the moisture is mostly gone. Only then will I take the oven up beyond the 197F which is the BP of water at my altitude.

I bought a cheap ceramic heater ($18) with a 1500 watt element and rewired it to bypass the thermostat and to wire the fan independently. I have the fan going constantly and the heating element switched with a PID controller. It is holding the air temp in the oven steady within 1 degree F and having no trouble maintaining this temp. At this point (two days into it) the outside of the dome is up to about 160F and slowly increasing over time.

That is a bit much for one post, so I'd better shut up now. I'd appreciate any feedback on my ideas.

Best,

Mark

Last edited by drseward; 09-07-2009 at 04:35 PM.
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  #14  
Old 09-07-2009, 04:36 PM
Il Pizzaiolo
 
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Default Re: Colorado oven

Very nice, Be proud....

Is that a little heater you got going in there to help cure ?

Mark
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  #15  
Old 09-07-2009, 04:58 PM
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Default Re: Colorado oven

Quote:
I bought a cheap ceramic heater ($18) with a 1500 watt element and rewired it to bypass the thermostat and to wire the fan independently. I have the fan going constantly and the heating element switched with a PID controller. It is holding the air temp in the oven steady within 1 degree F and having to trouble maintaining this temp.
This is a great idea. Will it avoid cracking? Well, my dome wintered over under cover after it was built, and sat the following summer during the construction of the two story chimney. It was probably nine months after my dome construction that I did my curing fires. I got cracks, but I suspect my dome was so thin that it would have cracked no matter what I did.

We'll be watching your results with interest.
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  #16  
Old 09-07-2009, 05:14 PM
Il Pizzaiolo
 
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Default Re: Colorado oven

Great Idea,
I am a seat of the pants kinda guy, and what your saying makes a lot of sense to me. Once you reach equilibrium, you should be golden..

BTW I cured by the 7 day fire schedule after 28 days of air curing, (heat stop 50) to date I dont have a crack that I have seen inside or out,

There are so many variables in oven builds, mortar mixes, bricks and materials etc,, I think wheather or not your oven cracks couldnt possibly be answered definitvely.. We all do the best we can and hope for the best and hopefully learn from the misteaks others have posted and shared with us,, I am far from an expert and think I just got lucky with the right combination of things, and Voila no cracks (theres still time)
Mark

Last edited by ThisOldGarageNJ; 09-07-2009 at 05:17 PM. Reason: spelling
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  #17  
Old 09-07-2009, 05:21 PM
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Default Re: Colorado oven

I think you are exactly right. If my oven doesn't crack, there are too many variables to attribute it to my curing technique. Perhaps if it does crack, that will be more telling.

Mark
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  #18  
Old 09-07-2009, 07:41 PM
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Default Re: Colorado oven

Quote:
Originally Posted by drseward View Post
I appreciate all the comments.


I see two potential problems. First, the formation of steam could damage the structure. Second is the temperature differential that would exist in an oven mass heated above the boiling point of water with water still present. For instance, dry areas of the oven could heat up to many hundred degrees F while areas with retained moisture could not exceed the boiling point of water. That could create significant thermal stresses to the structure.
I think you are exactly right. I run the laboratory for an oil refinery. Without getting too technical, fractional distillation is the backbone of refining. Simply put, liquids turn into vapor at a specific tempertuare.
When we distill a crude oil that contains water, we have to hold the temp at about 98.5 C ( 195 F) until all of the water has turned to vapor. Only then can we raise the temperture.
When water turns to steam it expands to about 300 times it's liquid volume. When we do this too rapidly in a distillation column it fountains crude oil out the top. This is also why you do not put out a kitchen grease fire with water. You will end up cleaning it off the ceiling.
By maintaining that low temp until the outer temp reaches the boiling point of water you should be able to slowing release the trapped water without a sudden surge in pressure as the water expands.
As another thought, the mortar may look dry but is is really not. The dryer it becomes the harder it is. Some of the cracks that appear may be from the mortar being slightly wet and therefore weaker when the initial expansion and contraction stresses occur.

Just my 5 cents ( adjusted for inflation)

Bruce
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  #19  
Old 09-09-2009, 07:52 AM
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Default Re: Colorado oven

All I can say is, WOW!
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  #20  
Old 09-09-2009, 02:41 PM
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Default Re: Colorado oven

That dome looks perfect! Great work!
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