My Modified Barrel Vault in Texas

[david s]

Re: My Modified Barrel Vault in Texas

In kiln construction the end walls on a barrel vault should be inside the arch. If outside the arch steel bracing is used to prevent the end walls from tending to fall out. A large diameter arc exerts considerable lateral force at its base, a semicircle much less so and a catenery arch the best, although only if its base is about the same as its height. We are not building kilns so the temp extremes are not as destructive but the principles are the same.

If the barrel vault is a semi circle the lateral force at the base is very small, i don't think you have a problem. Where it can be a problem is when it is an arc of a larger diameter sitting on top of walls. Whether you cut bevels or rely on mortar to fill the gaps will not alter the forces on the arch. However if the mortar falls out (unlikely) then you lose the strength of the arch form.

[perks1018]

Re: My Modified Barrel Vault in Texas

Yeah, that was my original premise. Soldier courses are an accommodation to a flatter, catenary vault to raise the vault ceiling. A semicircular arch doesn't need any more height. Using heatstop refractory cement as a glue- 1/8 to 3/16 joints- makes the joined bricks virtually monolithic.

[perks1018]

Re: My Modified Barrel Vault in Texas

"A running bond does not a stronger arch make. Each brick in any arch is bonded on every side to another brick or two. What a running bond provides is a greater number of individual or different bricks- 6 instead of 4- for any given brick to be attached to. Look at any brick in a wall and count the number of bricks it has contact with and you'll see what I mean. A running bond simply makes the failure of any individual joint less catastrophic."

I apologize to all for the foregoing drivel. Don't know what I was thinking. After I posted it, I got to thinking about my carpentry and realized that a running bond is the masonry analog to the finger joint in carpentry which, when compared to the butt joint, is stronger by orders of magnitude. Sorry for the nonsense. A running bond is preferable to a stacked bond (or whatever the thing is called).

[brickie in oz]

Re: My Modified Barrel Vault in Texas

Had to look catenary arch up on wiki today. There was a complicated mathematical formula to explain that it is the curve formed when you hang a length of chain between two points. too hard for me

Here is more about why arches work and fail, its easy to understand.

Auroville Earth Institute


.

[david s]

Re: My Modified Barrel Vault in Texas

The Pantheon in Rome apart from being breathtaking internally is incredibly ingenious. To make the dome lighter in weight as it rose towards the top a lightweight aggregate was used progressively for the concrete mix. They used pumice, a volcanic rock, and had it carted from Pompeii to Rome, hundreds of kilometers away (lucky they had slaves). These ancient Romans knew their stuff, about architecture and labour management.
http://www.aviewoncities.com/rome/pantheon.htm

[brickie in oz]

Re: My Modified Barrel Vault in Texas

get its pozzolans (flyash from Port Augusta at present) from?

Like Tony would say, "they will bring it over in a GREAT BIG NEW SHIP from China"

[luca]

Re: My Modified Barrel Vault in Texas

Hey Perks1018; I have a couple more questions for you! First, you gave your inner dimensions as 31" deep by 28" wide. Since I've always had a fire burning in the back of the oven when cooking pizza, I'm wondering whether you feel "crowded" for cooking space when you put your pizza in? Secondly, in looking at your flue construction, I can see by the pics that you have supported half of the flue by constructing it next to or over the door arch; did you do anything special to support the flue on the interior side of the vault? Finally, have you made a door for your oven and/or tried to cook anything that requires low temps for long periods of time (e.g. bread, barbeque meats, etc.)? I'd be interested to hear how the little oven performs in these areas. Thanks!

[luca]

Re: My Modified Barrel Vault in Texas

I'm starting my barrel vault this week and could use some input. My hearth is a granite table (see pic) and I bought some 2" FB Board for hearth insulation, but since I'm in VT, I'm concerned about heat loss in fall/perhaps winter. So here are my questions: 1) Is the 2" FB enough insulation, or should I add an additional 2" poured vermiculite base? and 2) If I add the vermiculite, should I put the FB board under the vermiculite or on top?

[dmun]

Re: My Modified Barrel Vault in Texas

Two inches of refractory insulation is enough for all practical purposes. I'm concerned about your granite cooking surface. Granite has the reputation of cracking and spalling in contact with direct flame. Soapstone is the only natural stone that will work as a oven floor, and that stuff is pricey. I'd go with firebrick for your floor.

[luca]

Re: My Modified Barrel Vault in Texas

Thanks for the quick reply! I'll try again to attach a picture, but the insulation will be sitting on top of the granite, and then the soapstone (which I am using for a cook surface) will sit on top of the FB board. Your comment about the granite and heat is why I was thinking of adding the vermiculite layer first so that there is no heat issue with the granite. Do you still think the 2" FB board will be enough; even with cold-weather pizza making?

[dmun]

Re: My Modified Barrel Vault in Texas

Do you still think the 2" FB board will be enough; even with cold-weather pizza making?

Yes. I have 2 1/2 inches of insblock19 and i can cook all winter long. Moisture is more critical in cold weather cooking than excess insulation. The main thing is keeping the insulation you have dry.

[luca]

Re: My Modified Barrel Vault in Texas

I don't know if Perks1018 is still around, but I am halfway through my barrel vault and am puzzled by his picture 26 (photobucket) which shows the entrance wall to the oven. In this shot, there is a central brick above the square opening of the finished oven that supports the near end of the flue opening, but I can't see anything holding this key brick up!!Other than a hidden steel lintel, I'd like to know if anyone knows of any clever way to support a key brick which sits over the actual oven opening?! I've thought of using pins drilled into the brick on each side, but am concerned that metal in brick will expand and eventually crack the brick that it is meant to support. Any input on this would be greatly appreciated, as I'm ready to build the oven opening but not sure how to do it!

[dmun]

Re: My Modified Barrel Vault in Texas

I don't know if Perks1018 is still around, but I am halfway through my barrel vault and am puzzled by his picture 26

A link to the picture might help us answer your question.

[luca]

Re: My Modified Barrel Vault in Texas

Sorry; it's picture 26 at this link:
Pictures by perks1018 - Photobucket

or you can just go to page 4 of this thread and click on the same link.

[brickie in oz]

Re: My Modified Barrel Vault in Texas

Sorry; it's picture 26 at this link:
Pictures by perks1018 - Photobucket

or you can just go to page 4 of this thread and click on the same link.

I should imagine with some expansion movement it would just fall out.