losing heat fast on the floor...

[junglepizza]

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?

[Dutchoven]

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

[dmun]

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?

[james]

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

[Xabia Jim]

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

[Frances]

Re: losing heat fast on the floor...

Good luck, nobody likes soggy bottoms

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

Sorry, couldn't resist...

[gjbingham]

Re: losing heat fast on the floor...

Nice, Frances, nice!

A picture might be worth 10,000 words on this oven, huh?

[Frances]

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.

[junglepizza]

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

[jengineer]

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

[dmun]

Re: losing heat fast on the floor...

I also see brick joint damp marks on the outside of your stucco. Insulation between the brick dome and the cladding is every bit as important as the insulation under the floor. Having a well insulated dome will let your dome heat up and reflect down on your cooking floor.

And yes, sand and gravel under your oven may be leaking a lot of heat, unless the gravel is volcanic pumice or something insulating.

The good news is that your dome is so high, you will have room to raise the floor if needed for cooking performance. Be a better hight to work from, too, from the looks of things.

[Les]

Re: losing heat fast on the floor...

Jackie,

This isn?t solving your problem, but what is in the wheelbarrow? Is that what you are firing the oven with?

Les?

[gjbingham]

Re: losing heat fast on the floor...

I like the idea of raising the floor. 2 inches of isoboard then a layer of brick on top, perhaps even half thickness brick would help a ton. I agree that sand and gravel under the floor is most likely sucking your floor heat away faster than you can put it in there.

[berryst]

Re: losing heat fast on the floor...

My thoughts.
It seems to me that if you tried a commercial pizza stone set up on a couple of bricks... would heat up fast. Hot air would circulate under and radiant heat above. Seems like it would work for pizza. Banks of hot coals around the stone could not hurt. Seems like it would e a quick cheap fix. The worst case scenario is you still have the stone if it doesn't work

[christo]

Re: losing heat fast on the floor...

Cool looking rustic oven!!!

As other have said, Insulation under the floor and over the dome is key.

If your floor is brick, you should be able to pull most of them out and resuse them. Id leave a row or two of bricks at the wall to keep the dome stable.

You might be able to excavate some of the gravel and sand and replace with vermiculite concrete mix to the 4 to 6 inch thickness referenced eariler. If you don't want to change the height of the floor, when replacing the bricks I'd leave a gap that will fill with ash to isolate the new floor from the bricks you could not pull out at the sides of the oven. That should leave you with a isolated floating floor that will absorb heat and keep it much longer. If you go this way - please be careful as the oven looks plenty heavy and a collapse could be a tad bit problematic for someone crawled up inside the oven....

By keeping a fire in the oven you should get enough refelctive heat to cook the top of the pizza without insulating the top dome. It will lose heat quickly so keeping consistent heat for baking/roasting might be a challenge. This might be a tradeoff if it is important to you to keep the traditional look of the oven. And you can always go back later and add insulation to the dome....

My 2 cents!

Have fun!

Christo