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  #111  
Old 10-16-2012, 02:26 AM
Laurentius's Avatar
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Default Re: Barrel Vault in So. Cal.

Hi Bill,

From looking at your vent design, I would say that you will get a hellva lot more water and moisture via your vent than you ever would via migration or stucco fissions. My oven has stucco and in the last two years we have had numerous typhoon with sheets of horizontal rain and the problem I had was rain seepage in my arch, which has porous fire bricks. I used a sealer on them and no further problem.
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  #112  
Old 10-16-2012, 01:43 PM
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Default Re: Barrel Vault in So. Cal.

Bill,
i think your idea is a sound one. if you place your hand over the vent while firing, you should feel the moisture if the insulation is wet. I incorporated a vent in my insulation layer in the support for the flue (see pic) moisture can escape between the two terra cotta caps.
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  #113  
Old 10-16-2012, 03:25 PM
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Default Re: Barrel Vault in So. Cal.

Hi David,

I'm not trying to be argumentative. The moisture that you feel in not a scientific indication that your insulation is wet, it does indicate the present of moisture. In your case terra cotta, which is capable of absorbing moisture out of the atmosphere is more probably culpable than the insulation. Have you ever done terra cotta cooking. I feel that if you have followed proven directions of hundreds if not more who have successfully completed their ovens, then assumptions shouldn't play in the outcome. When we encounter a problem, we should be scientific and methodical in finding a solution or giving advice. I would suspect that more than half of us probably had more water in the mortar of our domes and insulation than we should have had before we went to the next stage. Many of us had to have the fruit of our labor and just fired the thing up, devil may care. Others went from single match, candle, light bulb, progressing to an inferno, with the smiling baby perched on top, knowing " I did it right". The oven is not a Timed Bomb, waiting to explode, it might crack.
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  #114  
Old 10-16-2012, 11:27 PM
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Default Re: Barrel Vault in So. Cal.

Quote:
Originally Posted by Laurentius View Post
Hi David,

I'm not trying to be argumentative. The moisture that you feel in not a scientific indication that your insulation is wet, it does indicate the present of moisture. In your case terra cotta, which is capable of absorbing moisture out of the atmosphere is more probably culpable than the insulation. Have you ever done terra cotta cooking. I feel that if you have followed proven directions of hundreds if not more who have successfully completed their ovens, then assumptions shouldn't play in the outcome. When we encounter a problem, we should be scientific and methodical in finding a solution or giving advice. I would suspect that more than half of us probably had more water in the mortar of our domes and insulation than we should have had before we went to the next stage. Many of us had to have the fruit of our labor and just fired the thing up, devil may care. Others went from single match, candle, light bulb, progressing to an inferno, with the smiling baby perched on top, knowing " I did it right". The oven is not a Timed Bomb, waiting to explode, it might crack.
I admit I am a fan of incorporating a vent into the insulating space. Feeling the moisture at the vent is not a definitive test that there is moisture there, but I did say "... you should feel the moisture if the insulation is wet" indicating that the vent is doing its job. Having the experience of cracking the outer shells of two ovens I concluded that it was the pressure of the steam that was the culprit so incorporated a vent to help alleviate the problem. Living in the tropics we get quite a deluge of rain over about three months and during that time the uncovered, but waterproofed oven still gets pretty wet and we don't really use it then. When it is time to refire it, the oven takes a few long gentle fires to restore good function again. I am convinced that the vent does a good job in helping it to dry internally.Of course the water will eventually find its way out, just the vent helps. By using Terra cotta, which is porous, water is shed from the surface, perhaps a minuscule amount may enter but this is inconsequential.
I hope I have not left anyone with the impression that their oven could be a "time bomb" I'm sure I've never suggested that, you are correct, it will only crack the outer shell.
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  #115  
Old 10-17-2012, 10:07 PM
WJW WJW is offline
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Default Re: Barrel Vault in So. Cal.

Laurentis,

I agree that the vent as currently constructed will allow far more water in than it would vent. That being said, there is no hood on it now. Our rain is very predictable here in coastal southern california. We get essentially no measurable rain until November. And no significant rain until December.

I plan to get a good aluminum hood over that vent this coming weekend.

Other than the absence of the hood, do you have a problem with the design of the vent?

Bill
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  #116  
Old 10-18-2012, 02:38 AM
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Default Re: Barrel Vault in So. Cal.

Hi WJW,

I had planned not to make anymore comments, but since you asked I will give my honest opinion. If I was determined to vent as you are, I would try to design one that was motorized very simular to the fans used on old computers. If there were any moisture I would feel more assured that it was being driven out. Your design is static and large, which implies to me that when the oven is heated, warm moist air rise, some will escape but a great portion will condense on the ceiling of that void, but on rainy cool day the moisture will seek low levels. You stated that you don't get much rain, what about high humidity, or fog. I think that if your oven is used often it might be alright. Thanks for asking.

Lawrence
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  #117  
Old 10-18-2012, 08:24 AM
WJW WJW is offline
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Default Re: Barrel Vault in So. Cal.

We get very little humidity and very little fog. We get about 13 inches of rain per year...with almost all of that falling in December, January, and February.

There is no "void" at the top of the oven enclosure. The entire space is crammed with perlite (as you can see by looking at the picture of the vent).

Condensation is not likely, in my opinion, to be the source of moisture. And even if it were, condensation would be a problem with any style enclosure. No enclosure is air-tight. Humid air goes where it will.

My guess is that any significant moisture which gets in over time is likely to come from a heavy winter rainstorm which allows water to get in through either cracks in the stucco on top of the vault/enclosure, or through cracks on the countertop which would allow water to migrate to the slab, and then laterally to the insulation board sitting under the oven.

Frankly, even if I did get some condensation in there, I don't care. I don't believe that will negatively impact the performance of the insulation. What would concern me would be the prospect of water actually dripping/flowing in during a storm. If that happens I want somewhere for it to go when I fire up the oven. It seems to me that a vent is a tried and true solution for getting rid of moisture-laden air in such a situation. But I don't claim to be an expert and certainly have no problem with hearing contrary opinions.

Currently I have no cracks in my stucco that I can see. But in five years...who knows. I still haven't done my counter top...obviously I will take what steps I can to minimize the possiblity of water intrusion through lateral migration across the slab.

I don't think anything motorized is needed. Frankly, I don't see moisture intrusion is much of an issue in light of our cliemate, but I see zero down side to putting a vent on so long as it is properly hooded.

Just my opinion.

Bill

Last edited by WJW; 10-18-2012 at 09:17 AM.
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  #118  
Old 10-18-2012, 02:32 PM
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Default Re: Barrel Vault in So. Cal.

"The prospect of water actually dripping/flowing in during a storm", is more likely to get in that big-assed vent, than the pores of the stucco. "Frankly, even if I did get some condensation in there, I don't care. I don't believe that will negatively impact the performance of the insulation". I concur, if you believe that, why vent at all? Five years down the road? You might be dead, cripple or crazy, thinking that something bad or good will happen, doesn't make it so! For you information: Perlite, "when it reaches temperatures of 850-900 degrees C, it softens(because it is a glass). Water trapped in the structure of the material vaporises and escapes and this causes the expansion of the material to 7-16 times its original volumn"(wikipedia). If this is true, that means the your perlite layer is never dry. If you dome is covered with a proper ceramic blanket, the surface of the blanket is never 850-900 degrees C, meaning the perlite never vaporise its moisture. So whats the point of the vent, a feel good value. IMHO.
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  #119  
Old 10-18-2012, 10:30 PM
WJW WJW is offline
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Default Re: Barrel Vault in So. Cal.

How is water going to get in a vent which has a hood over it sheilding it from rain?

It's an oven not a submarine.

Assuming water vapor does get into the perlite layer (through humidity or otherwise), what makes you think the perlite needs to get to 800 degrees to vaporize water? Your link is talking about the temp needed to puff or expannd the perllite itself...not the temp needed to turn water to steam...or sufficiently energize the molecules so as to increase the rate at whisch they diffuse through the air.

My perlite has already been heated to 800 plus degrees...long before I bought it. Now it is a big bunch of open cell insulation which air and water vapor can travel through with ease...assuming there is somewhere for the air and water to go.

Assuming that it does get moist in there, heating that pearlite layer to 250 defgrees, or 200 degrees, or even 150...will drive water vapor out far more effectively with a vent than without one.


Why is it that attics are vented with vents such as mine? The vents are passive. They are open to air...presumably they are just as likely to allow water in as mine is. Yet they are there. Why?

As far as a feel good value...that may be true to a certain extent. Ditto for the extra three pieces of rebar I put in the slab. Ditto for that third layer of stucco you put on your oven.

The point is that it cost me about ten dollars to put that in. Passive venting is used all the time to remove moisture from enclosed structures which are otherwise at risk for having trapped, moist, dead air. Those passive vents are properly hooded and result in a net drying effect...otherwise you wouldn't see them on attics, machine shop walls, pool equipment sheds, green houses, etc.

I get it that you think a vent is a bad idea on an oven. Can you tell me why? Why is it that you think water will get in through a hooded vent? What makes you think that will happen...specifically...rather than just saying it is so?

Bill
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  #120  
Old 10-19-2012, 12:28 AM
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Default Re: Barrel Vault in So. Cal.

Quote:
Originally Posted by WJW View Post
How is water going to get in a vent which has a hood over it sheilding it from rain?

It's an oven not a submarine.

Assuming water vapor does get into the perlite layer (through humidity or otherwise), what makes you think the perlite needs to get to 800 degrees to vaporize water? Your link is talking about the temp needed to puff or expannd the perllite itself...not the temp needed to turn water to steam...or sufficiently energize the molecules so as to increase the rate at whisch they diffuse through the air.

My perlite has already been heated to 800 plus degrees...long before I bought it. Now it is a big bunch of open cell insulation which air and water vapor can travel through with ease...assuming there is somewhere for the air and water to go.

Assuming that it does get moist in there, heating that pearlite layer to 250 defgrees, or 200 degrees, or even 150...will drive water vapor out far more effectively with a vent than without one.


Why is it that attics are vented with vents such as mine? The vents are passive. They are open to air...presumably they are just as likely to allow water in as mine is. Yet they are there. Why?

As far as a feel good value...that may be true to a certain extent. Ditto for the extra three pieces of rebar I put in the slab. Ditto for that third layer of stucco you put on your oven.

The point is that it cost me about ten dollars to put that in. Passive venting is used all the time to remove moisture from enclosed structures which are otherwise at risk for having trapped, moist, dead air. Those passive vents are properly hooded and result in a net drying effect...otherwise you wouldn't see them on attics, machine shop walls, pool equipment sheds, green houses, etc.

I get it that you think a vent is a bad idea on an oven. Can you tell me why? Why is it that you think water will get in through a hooded vent? What makes you think that will happen...specifically...rather than just saying it is so?

Bill
Hi Bill,

This is why. All of the WFO that I have seen, that are rendered, or concrete, cement, adobe or just plain mud are closed systems, be they insulated or not. I think the cladding of the oven were primarily to protect them from the elements(rain, snow, wind storms,ice), because they were a valuable assest to the community a large( one oven per village= the baker). They have a very good record without venting. The other types, be they igloo or barrel, some people chose to build housing around, some use modern scientific insulation others use everything from broken glass, to air. Many of these are vented for various reasons. I never said that I think water will get in. What I'm saying it that in the laws of probabilities, your vent is more likely to cause a water or moisture problem, than your stucco. Now one question for you. With all the stucco covered oven that you see on this forum, why do you feel that your is most likely to crack or suffer water damage, without a vent?
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