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  #281  
Old 12-16-2012, 08:45 AM
Peasant
 
Join Date: Nov 2012
Location: Arizona
Posts: 33
Default Re: Oven Curing

First off, thanks to all of you that post on here....it is extremely helpful to those of us just starting out.

I won't lie to you and tell you that I've read this entire thread, but I've read large portions of it. I have finished my dome as of Thursday, 3 days ago. My oven is not a brick oven, but rather a clay oven. My dome is made of 1 part fire clay mixed with 3 parts sand.

I understand the process of curing, but I was wondering, do any of you know how much of this is applicable to a clay oven? I imagine the process is similar, but I'm assuming clay will be more delicate than concrete/mortars. I actually have a break from the rain and the sun is out today, so I'm hoping to pull the sand form out from inside of the dome tomorrow.

Is a week long enough to let the oven sit before building fires? I've made it to this point without any disasters...I'd like to keep that streak going! Thanks in advance for any help/advice.
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  #282  
Old 12-16-2012, 09:20 AM
Il Pizzaiolo
 
Join Date: Jun 2009
Location: So. Orange County, CA. USA
Posts: 1,156
Default Re: Oven Curing

Mooveebuff, Curing a clay oven is going to be a bit different than brick.. Although firebrick starts as clay and sand that won't break down in heat. Firebrick is quite porous and so water can move out of the brick and mortar relatively fast compared to an all clay structure. The variables that you're going to be dealing with are how thick the walls are and how fine the clay is. Clay is microscopic planes of material and when water is added the water occupies the space between these planes and this gives the material plasticity and this water also forces the material to expand. This is why building on clay, expansive soil, is not a good idea.

Some ceramics, Raku comes to mind, can be wet and fired in this condition and because of the large proportion of heat stable aggregate in the body, the steam can vent, and with fire, magically you have a cup or bowl. My point is that if the clay you used has a significant portion of aggregate, then steam and vapor will move and the structure will dry relatively quicker than otherwise.

Ok, because you are using clay, if it were me, I'd be going very slow and carefully. The center of the clay will not dry easily. Start with a quartz work light and move air through the oven and over the exterior of the oven. The light will warm the interior and help to move air. As the interior dries you can start to close the entry and this will help to contain the heat.

You spent time with the build, take more time than you'd like with the curing and you'll have long use of your oven.

Chris

Last edited by SCChris; 12-16-2012 at 09:25 AM.
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  #283  
Old 12-16-2012, 11:22 AM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,720
Default Re: Oven Curing

It is too late now, but one trick is to add fibres to your mix that are designed to burn away at low temp leaving a network of mini pipes that water vapor can escape through. This is what proprietry refractory castables contain.Polypropylene fibres are usually used and the fibres have a melting point of 160 C. I think adding horse manure to the mix for a cob oven has a similar effect. Chris, while I agree with almost all you have said, it has been my experience that clays with a high proportion of grog are actually slower to dry than finer bodies. One trick to use is to throw some plastic over the dome to test whether there is any condensation under it. This will tell you if water is still being expelled.
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  #284  
Old 12-16-2012, 02:41 PM
Peasant
 
Join Date: Aug 2011
Location: Skagit County, WA
Posts: 28
Default Re: Oven Curing

I put a heat lamp in my FB oven for days, but at some point you will have to have fire. Keep the fire small and resist the impulse to make it larger even if you have kept it small for a long time. What will happen is that a small fire will continuously drive off water, tending to hold the mass at a certain temperature. If you are monitoring temperature, it will seem like you aren't getting anywhere. Once the water is driven off, the temperature of the clay will start to rise again, without having to increase the fire size. Keep it small and steady
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  #285  
Old 12-16-2012, 06:14 PM
Journeyman
 
Join Date: Oct 2005
Location: Gilbert, AZ
Posts: 420
Default Re: Oven Curing

I used a propane weed burner and adjusted the flame as needed. Also: Make sure that you have the flame hit some bricks placed in front of your bricks as a flame barrier. You do not want to have the flame hitting your brickwork and make a nasty old crack (like what happened to me on day 3 or 4 and I determined the solution!)

As a side note: I use my weed burner to start the fire as well - works like a charm.
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  #286  
Old 02-27-2013, 07:42 AM
Serf
 
Join Date: Feb 2013
Location: nr Swindon UK
Posts: 6
Default Re: Oven Curing

I have seen on this thread (read it all!!) some reference to using a gas burner to heat the oven however there were also a couple of comments that such use of gas is dangerous / should not be discussed on the board.
Can anyone throw any light on this as obviously doing something dangerous isn't always a great idea
Thanks
Miles
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  #287  
Old 04-04-2013, 11:43 PM
Master Builder
 
Join Date: Oct 2012
Location: Los Angeles
Posts: 701
Default Re: Oven Curing

I think as long as there is air flow so the gas vents out it should be okay.
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  #288  
Old 04-10-2013, 09:08 PM
Master Builder
 
Join Date: Oct 2012
Location: Los Angeles
Posts: 701
Default Re: Oven Curing

I officially started the curing. I had the propane weed burner in there for about 2 hours, had it on its lowest setting. Stacked a few fire bricks to diffuse the flame/heat. The hottest the top of the dome got was just shy of 200F. The chimney also seems to be drawing pretty well. Hope i can continue some more tomorrow. Do you guys recommend a constant steady heat? For example keep the heat at 300F for a few hours?


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  #289  
Old 06-11-2013, 12:13 PM
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K79 K79 is offline
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Join Date: Nov 2012
Location: Maine
Posts: 389
Default Re: Oven Curing

Hey guys I'm at post 130 in this thread and was reading about using charcoal briquettes because it's less direct heat on the dome. Could I burn a nice fire in my firepit and transfer these coals into the oven and essentially never start a fire in the oven for the curing process.... for the first few hundred degrees anyways. Also what about a few canned heat containers?

Last edited by K79; 06-11-2013 at 12:39 PM.
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  #290  
Old 06-11-2013, 02:27 PM
cobblerdave's Avatar
Il Pizzaiolo
 
Join Date: Jan 2010
Location: brisbane australia
Posts: 2,264
Default Re: Oven Curing

Gudday
The bricketts work well because it is hard to maintain and feed a small fire over a period of time. Not used canned heat so I will not comment.
Regards dave
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