Started my Build in Georgia

[david s]

Re: Started my Build in Georgia

Hi David,

there is no way an insulated structure will benifit in the eliminated of moisture .

Except as previously explained, the insulation will help even out the temperature difference.
It will certainly reduce the rate at which the moisture is removed. Castable refractory manufacturers recommend that when eliminating moisture, if steam is visible then you are going at it too hard and to back the heat off. Presumably the same would apply for the mortar in an oven constructed of brick.
Like I said before, you can do it quickly and risk damage, but you can never do it too slowly.

I've certainly built defects in things , but I'm sure I've never been guilty of defection.

[Laurentius]

Re: Started my Build in Georgia

Except as previously explained, the insulation will help even out the temperature difference.
It will certainly reduce the rate at which the moisture is removed. Castable refractory manufacturers recommend that when eliminating moisture, if steam is visible then you are going at it too hard and to back the heat off. Presumably the same would apply for the mortar in an oven constructed of brick.
Like I said before, you can do it quickly and risk damage, but you can never do it too slowly.

I've certainly built defects in things , but I'm sure I've never been guilty of defection.

OK, David the builder is slowly increasing the heat build up as recommended by the sage wisdom of our predecessors, would it be better with or without the insulation? If you are not taking the structure into thermal shock, the evening out the temperature difference would be a moot point, since the absorbability of heat would be relative, the heat would not pool in the ceiling it would at a measurable rate be transferred into the dome or barrel and if there isn`t any insulation into the slab itself, becoming a heat sink. Yes, you can do it too slowly if time is a factor.

[cobblerdave]

Re: Started my Build in Georgia

G'day
Letting the oven sit for a few days between heating allows the moisture to migrate from the damp brick interior to the dry surface parts of the oven. This way it's at the surface ready to teased out with the next heating.
My ovens wet from the stowage being flooded with the recent rains. I'll be getting a fire in it tomorrow morning for an hour. Then it's to be left open till probably next Sunday till another fire. Leaving it open and the wind will do the job till Sunday. It's probably as wet as it was when I built it. It needs drying out not "curing fires". It's got 2 matching hairline cracks above the entrance and I'm not going to crack any thing else in a rush to get it cooking again.
Regards dave

[david s]

Re: Started my Build in Georgia

would it be better with or without the insulation? If you are not taking the structure into thermal shock, the evening out the temperature difference would be a moot point, since the absorbability of heat would be relative, the heat would not pool in the ceiling it would at a measurable rate be transferred into the dome or barrel and if there isn`t any insulation into the slab itself, becoming a heat sink. Yes, you can do it too slowly if time is a factor.

Practice demonstrates the huge temperature difference in the crown of the dome and the base of the dome , as well as the outer floor temp.of a wet , new oven. Expansion is proportional to temperature increase which sets up great stress on the structure. This is exactly what thermal shock is (see link below), the ability of a material to withstand expansion or contraction caused by heating or cooling. Unfortunately by using wood flame to dry the oven, which is difficult to control, as heat rises the flame impingement on the crown of the oven simply exacerbates the problem. I'm not advocating which way the oven should be dried, merely providing some advantages for doing it with the insulation on, since you suggested it is more efficient to dry it with the insulation off. There is much to consider and of course time is a factor. I've driven water out of a lot of ovens and done it both ways. Let members decide how they would like to do it, but I've heard time and again how ovens have suddenly developed cracks in the latter stages of the drying out process (I dislike the term "curing").
Many of these may have been avoided if the drying were done more slowly.
http://www.wisegeek.org/what-is-ther...#didyouknowout

[DavidApp]

Re: Started my Build in Georgia

Hello All

In using a LPG burner I may have exuberated the problem because unlike a small fire there is little radiant heat supplied to the lower part of the dome. I did add a deflector plate later in the heating cycle but It did not seem to make much difference.

Maybe the burning barbeque charcoal spread around the oven would give a more controlled even heating. I seem to remember someone here did that a while ago.

David

[texman]

Re: Started my Build in Georgia

David

i cant explain the chemistry, but i know a lot of moisture is created from burning natural gas and propane. i think the charcoal, small wood fires are very effective for curing. just go slow. I used wood only. I live in a dry part of the world so i had very low humidity to deal with. I copied this info on burning propane fwiw.

Texman

Combustion

Water becomes a by-product of propane through the process of combustion. Combustion occurs when there's between 1.8 percent to 8.6 percent propane and 91.4 percent to 98.2 percent air. Any more or less propane, and combustion can't occur completely. This results in an improper equation and creates deadly carbon monoxide gas. The equation for the complete combustion of propane is as follows: 3CH8 + 5O2 > 3CO2 + 4H2O.

Water Production

Propane's three-carbon alkane (3CH8) is added to five molecules of oxygen (O5). When heat is applied to the mixture, combustion occurs, and the atoms begin to interact violently. The electrons and protons push and pull on each other until balance is restored, creating carbon dioxide (3CO2) and water (4H2O). This process is continued until the propane, oxygen or heat is exhausted. The combustion of propane then results in the creation of relatively large amounts of water.

Usability

The water produced by propane mixing with too little oxygen is unusable for most applications, such as drinking water. In fact, the water vapor is so minimal that usually the water burns up right along with the propane. It's actually the evaporating water, combined with carbon dioxide emissions, that causes propane to burn with a visible flame.



Read more : Why Burning Propane Makes Water | eHow

[david s]

Re: Started my Build in Georgia

Even though folk may be exuberant about the use of propane to dry their oven its discussion on this forum has been banned because of its possible dangers.

[sharptailhunter]

Re: Started my Build in Georgia

I'm curious to know if anyone has ever tried a hydrophilic (water-loving) substance on the exterior of a recently completed dome? There are plenty of cheap options like cat litter, sugar, salt, even saw dust is absorbant. I know it wouldn't replace internal drying fires but in theory, maybe could help coax some water out. It'd be easy to measure just how much, if any, water it did absorb.

[Laurentius]

Re: Started my Build in Georgia

I'm curious to know if anyone has ever tried a hydrophilic (water-loving) substance on the exterior of a recently completed dome? There are plenty of cheap options like cat litter, sugar, salt, even saw dust is absorbant. I know it wouldn't replace internal drying fires but in theory, maybe could help coax some water out. It'd be easy to measure just how much, if any, water it did absorb.

Why! It would absorb as much moisture out of the air as it would the structure, unless you encased the whole structure in a moisture proof barrier of some type. What a mess the logged sugar or salt that wicks into the bricks would make. Heat and air circulation is the best bet.

[sharptailhunter]

Re: Started my Build in Georgia

Yes, I failed to mention the barrier for the substrate-to-air. Was just curious, sounds like dry heat and air flow are best. Hope I didn't hijack or intrude. Carry on :-)

[GianniFocaccia]

Re: Started my Build in Georgia

It would absorb as much moisture out of the air as it would the structure, unless you encased the whole structure in a moisture proof barrier of some type

Its fairly common to enclose new stacks of wood in dark-colored tarps that trap greenhouse energy. The moisture released from the warmed logs condenses on the inside of the tarp and drips to the ground. Should work with an oven to a degree.

[DavidApp]

Re: Started my Build in Georgia

Fired the oven the last two nights getting the dome to 650 degrees then 750 degrees the lower section of the dome got to 400 degrees. Let the fire die down a bit then shut the door to let the oven temperature equalize. This morning the temperature was still 380 degrees and I have only got one layer of insulation on the dome.
I am going to continue with these fires for several more heating cycles to see how the lower section of the dome heats up.

I notice that the crack in the inner arch is not opening up as much now as the oven heats up. Should I try to rake the mortar out of the joint and repoint It or just do nothing?

David

[david s]

Re: Started my Build in Georgia

Fired the oven the last two nights getting the dome to 650 degrees then 750 degrees the lower section of the dome got to 400 degrees. Let the fire die down a bit then shut the door to let the oven temperature equalize. This morning the temperature was still 380 degrees and I have only got one layer of insulation on the dome.
I am going to continue with these fires for several more heating cycles to see how the lower section of the dome heats up.

I notice that the crack in the inner arch is not opening up as much now as the oven heats up. Should I try to rake the mortar out of the joint and repoint It or just do nothing?

David

I've found attempting to repair cracks is usually not successful, you'd be better just living with it.

You can test whether you've eliminated the moisture by throwing some plastic sheeting over the oven to see if there is any condensation on the underside of the plastic.

[DavidApp]

Re: Started my Build in Georgia

Hello David

Thanks for the plastic tip. I will try that tomorrow.

Fixing the crack was only a thought and I assumed it would only be cosmetic at best.

The top down fire seems to be a winner. I put a pine cone on top of several layers of wood with some kindling piled on the cone. balled up paper to start the pine cone.

David

[DavidApp]

Re: Started my Build in Georgia

No signs of moisture on the plastic.

The dome started to clear in one spot. Temperature on the lower part of the dome went from 420 on the soldier course 380 on the next two courses then to 500 on the next course.
When the fire died down I shut the door to let the heat soak in.

David