Barrel Vault in So. Cal.

[Laurentius]

Re: Barrel Vault in So. Cal.

Hi WJW,

Darn, too much beer can ever make an WFO, tipsy.

[WJW]

Re: Barrel Vault in So. Cal.

Jim:

Thanks for the nice words. As for your questions...

Mass:
I was focused (probablly too focused) on keeping mass down in order to reduce the time needed to bring the oven up to pizza cooking temp. Now that I've built the thing, and now that I've cooked with it a lot I think I have a better picture of what is important than I did when doing the pre-build research. I've now done approx. fifteen-twenty bread bake days (coming up on 250 pounds of flour.), an equal number of pizza parties for in excess of twenty people, and twenty or so slow cook events, such as pork shoulder, osso bucco, etc. So I think I've got a pretty good understanding of how it works now.

The hearth of my oven is currently 2.5 inches of firebrick. The walls are 4.5 inches thick. The roof is 4.5 inches thick. For cooking pizzas, doing bread bakes of up to 20-25 loaves, and doing slow cooks on day two and day three....this is plenty. Nothing more is needed. Period. The floor has enough mass that, even when cooking pizza for thirty to forty people, I have never run into a situation where the floor had cooled to the point that it wasn't cooking properly. I typically have some type of pizza disater once or twice during a forty minute cook, that I have to use coals to burn the hearth clean. And even if I don't, there's enough burned flour cheese scraps etc, that I will rake coals onto the hearth after twenty pizzas no matter what anyway. So hearth heat is a non-issue for me. This is probablly also due to the fact that I have quite a bit of area to work with so even when doing three pizzas at once (my max) , there are areas that are "resting".

I think the most important factor in maintaining heat over time (for next day bakes and slow cooks) is insulation. My oven is well-insulated so it stays hot a long time. That being said, mass is obviously important too. And while I think the low mass model I have built is great for anything but using it for comercial bread-baking purposes, I also have my doubts about how much extra burn time would really be needed if my oven had an extra few inches of mass.

And what I have learned is that the way I use my oven, there really is no need whatsoever to have an oven that I can heat up and cook pizzas in on short notice. The reality is that most of my cooking (whether it is pizza or bread) is on weekends. So if I'm going to have a party with guests arriving at seven, it makes no difference to me whether I light the fire at three or four or five. It's just a non-issue. And with pizza for just a few people, the demands placed upon the oven are so minimal that you have enough saturation after ninety minutes of fire anyway. And even if cooking for forty, two and a half hours is more than enough time to saturate my oven. But who has a party for forty on less than three hours notice??? So I think all of my focus on reducing mass to reduce heating times was, while technically correct, not a very big concern in real world use.

And with bread, I'm finding that a fire lit the late the night before a morning bake and allowed to burn out on its own in the middle of the night actually does the best job in fully saturating the oven so that I light second small fire the next morning to quickly bring up the surface temps. That goes out after an hour or so, I seal it up to equalize as the dough is proofing, and all is good. So once again...quick heating isn't a significant benefit.


With the amount of bread baking and slow cooking I'm doing, the low mass model is fine. But I'm thinking about changing to a quasi-commercial scale. My daughter is a foodie who has always wanted to do some kind of food-based business. We're sort of kicking around the idea of selling sourdough at Farmer's market as a possible long term transition into some kind of larger food based business for her. So...I am seriously considering putting an extra layer of firebrick on the floor to increase mass by 2.5 inches.

Right now, with the mass I have I can do four bakes on a single firing. (Temps are starting in the 580 range...last bake starts in the 460 range). Four bakes equals approximately thirty to forty loaves of bread assuming loaves of 1.25 to 2.0 pounds each. If I really do decide to bake sourdough to sell, I'd want to do no less than 100 loaves on a bake day and ideally closer to 150. To do that efficiently, I'd need to add some mass. It won't be hard to do as I can simply lay the bricks in there, so I'm considering it.

The Vent:
The vent in the back is to vent moisture should some ever get in there. It seems likely to me that moisture will eventually work its way in. I figured there is no down side to a vent so long as I put a proper hood over it.

Bill

[Laurentius]

Re: Barrel Vault in So. Cal.

Hi WJW,

When you say, Vent. Are you talking an actual vent within the dome itself, or within the enclosure? Sorry your oven is not enclosed. I'm somewhat like you, I use my oven for baking and cooking and very little for pizza. The only time I have a moisture problem is after cooking pizza and having a clean oven, I fill it up with unseasoned wood to dry. If I leave it sealed in the oven the next day I will find condensation under the door. All I have to do is open the door to allow air to circulate and problem solved. Even if you use it on a commercial level, moisture is not going to be a concern from the oven. You know already that if you don't have enough bread in the oven, that you have to induce it get "Spring". The oven is dry saturated heat and in the 40-60 minutes of bread baking, your oven is as dry as Death Valley, in a drought at high summer.

[jim81147]

Re: Barrel Vault in So. Cal.

Bill , thanks so much for the insight . The more i read and study here the more i am changing my opinions .

[WJW]

Re: Barrel Vault in So. Cal.

By vent, I mean this.



The oven is enclosed in that there is a brick oven, completely encased in a layer of ridgid insulation. Then I built a framework around the top portion which had a four inch high void above the roof arch. There were also some voids on the side, but for the most part the sides and rear are just encased in concrete block which surrounds the three to four inch layer of ceramc insulation. Whatever voids were present were filled with perlite. Then the whole thing was enclosed in stucco.

My concern about moisture is the possibility of water either migrating through cracks in the stucco, or falling on the slab and then migrating below the insulation. With that in mind, it made sense to me to vent it so that if it does get water in there, I can then heat the oven and the moisture will have some place to go.

Bill

[Laurentius]

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.

[david s]

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.

[Laurentius]

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.

[david s]

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.

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.

[WJW]

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

[Laurentius]

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

[WJW]

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

[Laurentius]

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.

[WJW]

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

[Laurentius]

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

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?