#1  
Old 04-18-2008, 04:41 PM
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Location: Zihuatanejo, Mexico
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Cool losing heat fast on the floor...

We recently had an oven built down here on the Pacific coast of Mexico where traditional mud ovens have been used forever. It is a large oven - diameter of the floor is 63 inches and height of dome is 60 inches. Our opening is about 27.5 inches by 12 inches and there is not a chimney but there is a small circular opening about 6 inches in diameter on the side just above the floor. Once we get the oven up to temperature we have been splitting the fire into two and moving to both sides of the oven. The problem is that the floor in the center for cooking is dropping in temperature very quickly and the pizzas are not crisping up on the bottom. Any suggestions on how to control this better?
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  #2  
Old 04-18-2008, 05:02 PM
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Default Re: losing heat fast on the floor...

Is the floor insulated at all? You might consider letting some embers sit in the center of the oven even after you split the fire to soak some more heat into the floor but...if it is not insulated it will be a big heat sink
Best
Dutch
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Old 04-18-2008, 05:25 PM
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Default Re: losing heat fast on the floor...

Yes, this sounds like the "Oops no insulation" Or "someone told us that sand/pea gravel/broken glass is the traditional insulator for wood fired ovens" post. I hope I'm wrong.

If I'm not, there is not an easy fix. You can try to affix insulation to the bottom of the support slab (which if I'm right will be getting very hot) but this is a marginal improvement at best.

Let us know details. With any luck it's just a problem of not building a big/long/hot enough fire. Does your dome fire completely white?
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Old 04-18-2008, 05:54 PM
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Default Re: losing heat fast on the floor...

I agree with David,

Have you had some really good fires? Is the entire dome white and are you keeping a good fire going, with the flame lapping high into the dome?

You need that reflecting heat. Let's look there first, before thinking (worrying) too much about under the floor insulation.

James
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Old 04-18-2008, 10:48 PM
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Default Re: losing heat fast on the floor...

Interesting.....how about some photos of the oven, is it mud?

Lots of questions here....

Why split the fire? Do you start it in the middle? How long is it fired before first use? Is it a rip roaring fire? Are you getting flames to lick the dome and come down the other side?

Do you have some actual temperature measurements of the hearth? You say the floor is cooling too fast....does it work initially? Are some pizzas turning out ok?

What is the hearth made out of? How thick? What is under it?

You could build a fire cradle that can easily move your coals around and recharge the hearth for the next pizzas. There is a recent post on something like that.

I assume the hole is to provide air to your fire...Are you using a door between pizzas?

How many fires have you had so far? It's recently built....did it dry and cure properly?

Another thought was to have some hot pizza stones in there but I have not used them yet....

Good luck, nobody likes soggy bottoms
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Old 04-19-2008, 12:01 AM
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Default Re: losing heat fast on the floor...

Quote:
Originally Posted by Xabia Jim View Post
Good luck, nobody likes soggy bottoms

...except George's wife, apparently...

Sorry, couldn't resist...
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Old 04-19-2008, 10:09 AM
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Default Re: losing heat fast on the floor...

Nice, Frances, nice!

A picture might be worth 10,000 words on this oven, huh?
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Old 04-19-2008, 11:09 AM
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Default Re: losing heat fast on the floor...

Man you had me thinking a pic of you...!!!

Yeah, a picture of the oven by all means. Would make things easier.
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Old 04-21-2008, 12:05 PM
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Cool Re: losing heat fast on the floor...

Thanks to all of you who responded so quickly - sorry it took me a couple days to get back here.
Okay, I have put together a PDF of 10 photos showing construction but apparently it is too large to post here so I have attached 2 photos (hopefully). I am also happy to send an e-invite to see our entire oven and restaurant construction photos on Snapfish.com if you wish - please send me an email address if you choose this option.
Some answers to all of your questions:
The insulation is the entire base of the oven - they used gravel and sand - not sure what else.
Yes, we have had a number of fires and large ones. We allowed it to come up to 770F before splitting into two. Tried just moving to one side but the other side lost heat fast so we tried splitting to both sides and cooking in the center. We have an infrared thermometer that shows us that the interior is staying hot around 700F but the floor drops to about 625F after about 20 minutes of cooking.
Yes, we have had success with pizzas but not as crispy as we were hoping for. Was able to turn out 10 in succession but not quite as crispy as we want.
We do not yet have a door to close off oven but that is in the works - should we be closing door whenever there is no activity?
Thanks again, Jackie
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losing heat fast on the floor...-dsc02305_lr.jpg   losing heat fast on the floor...-dsc02377_lr.jpg  
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Old 04-21-2008, 03:06 PM
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Default Re: losing heat fast on the floor...

closing the door will cut off the air/oxygen supply to the fire.
The dome is quite high for pizza building.
Do you have access to high density insulating material? This would be stuff that they use in industrial furnaces. There are different material specs out here that may serve your purpose.
You are loosing your heat through the floor. can you pull out the brickks that make up the floor?

1. One suggestion would be a partial demolish the opening.
2. Add in 4 to 6 inches of vermiculite comcrete - read up on thios forum about the ratio of vemic to cement
2. Add in 2 inches of insulating board
3. Re-lay your floor.
4. you have now raised the floor by either 5 or 8 inches. or another way of looking at it you have lowered the dome.

stand by for others to add their suggestions
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