Saint Helena Oven

[dmun]

Make sure you have an diamond blade for your angle grinder - that stuff is HARD

[jahysea]

Originally Posted by dmun

Make sure you have an diamond blade for your angle grinder - that stuff is HARD

Ouch, I was planning to do it with the $5 abrasive masonry wheel.

Oh well, more tools. Hopefully my grinder is beefy enough for a diamond blade.

[jahysea]

Well, 7 days after finishing the dome I lit the first tiny fire. I've then lit 2 per day, one at night and one before leaving for work.

Some settling happened and a few no big deal cracks in the dome. I've sealed the dome cracks with some chimney stuff like caulk that says it is tested to 2000 degrees.

The bigger issue is that the arches in the front developed some cracks. I've realized that the base bricks have moved outward. They are "mortared" to the vermiculite/portland 8" shelf with just 50/50 sand firedust, which isn't very sticky, even when well cured.

I've taken the front arch partially apart and will remortar it after addressing the spreading.

I all along intended to pour concrete in front of the oven as a base for the granite tile shelf that will span the entire front (got to have a place to set your glass of wine while playing with the fire). I decided to extend that concrete base to wrap around the bricks at the oven mouth so that the concrete could hold those bricks from sliding outward.

So I formed it all in 2" high and poured concrete today. No rebar. I realize that the concrete will steal thermal mass from the oven slightly, but the tunnel opening on my oven is about 15 inches deep and the concrete butts up to only the outer 9 inches or so. I think I can live with that. The infrared indicates those bricks don't get real hot anyway.

The pictures probably tell a better story. The first one is of the spreading the arch base did. The rest show the concrete forms and concrete.

I'll reassemble the arch when I add the chimney.

[jahysea]

I also started the metal walls today. Got 2 done in a couple hours, the metal isn't as hard to deal with as I feared. I bought an abrasive metal blade for my chop saw but never bothered to dig the chop saw out, it wasn't that rough cutting the studs with my shiny new tin snips.

I did the back wall and one side wall. I also anchored the base trays into the fresh concrete mentioned in my previous post.

Weather and family fun permitting I should be able to finish all 4 walls and possibly the stringers for the roofing over the long weekend.

I plan to stucco the exterior and use spanish tile on the roof, to match our home.

[maver]

Originally Posted by jahysea

Ouch, I was planning to do it with the $5 abrasive masonry wheel.

Oh well, more tools. Hopefully my grinder is beefy enough for a diamond blade.

If you are concerned about the quality of your grinder consider purchasing a blade for a circular saw, if you have one. It would be easier with a circular saw to obtain a straight cut, plus you will have the ability to set a shallow depth of cut and make a few passes.

I would also suggest you consider buttressing the sides of your front arch (where you placed the metal stud next to the arch or, if there is room, behind it). I don't know anything about calculating load bearing for an arch, but I do know that the force of your arch as designed will push out on the sides of your entry. I think a few bricks mortared onto the side in that area would be wise for a masonry chimney.

[jahysea]

Well.... I have a old circular saw long ago designated solely for dusty crud work like cutting stucco with a masonry blade.

But. I'm cutting an arc. If it were made of wood I'd use a jigwaw. The rounded cut would be pretty tough with the circular saw alone. You gave me a great idea though. I'll vacate most of the cut with straight strips with the circular saw. Then I'll use my wet saw without the table and free hand the arc. It just has to be round enough to mortar.

Or I'll do as David suggested and use a diamond wheel on the grinder. Nice to have options.

Not having seen the materials yet, but knowing the sections are only 1' in length, how do they join together? Are they fluted to overlap each other I wonder, or are they straight and I will just mortar them together? If the latter, I suspect they will need additional support, which I can provide as they go through the roof.

You are correct in pointing out the force on the outside of the arch walls. Big cathedrals in Europe like the one in Lincoln England have giant extensions with piles of masonry outside along the walls (not sure of the architectural term) to keep the weight of the roof from pushing the wall outward and over.

I could easily make a little brick wall on either side of the arch tunnel walls. If I placed it on top of the concrete I just poured I'd be pretty confident they will never move. And nobody would ever see them as they will be inside the walls.

[Marcel]

(M) James wrote, in part:

"Does that seem to be the "best practice" (my old IT days showing through) method for the last few chains? Marcel, does that work for you, or are you ready to recommend the beach ball? "

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(M) In general, I'd like to see the plans include *many* optional approaches. I realize that we're not "skinning a cat" but I have seen a great variety of methods and materials. I would favor a basic recommended set of instructions with footnotes indicating a special section where alternatives could be viewed.

(M) Your "" makes me wonder if you are speaking tongue in cheek or just being friendly. I'll assume the latter and say that I have not used a beach ball but if I were to build another oven, that would be something I'd certainly try.

(M) Without having had actual "hands on" experience using any particular technique or material, I'm reluctant to take a pro or a con position. I tried balloons and had trouble with them popping so I figure a beach ball is far tougher, bigger (so it eliminates the need for styrofoam vanes) and a virtually perfect sphere. The builder could see the first 6? chains on the inside and only later employ the ball.

(M) I know that somewhere on this site there is a successful build using a beach ball. I could probably find the reference if anyone requests it. Beyond that, I'll stick with my old cliche' adage in red of Albert Einstein

Ciao,

Marcel

[Marcel]

[quote=jahysea]

"You are correct in pointing out the force on the outside of the arch walls. Big cathedrals in Europe like the one in Lincoln England have giant extensions with piles of masonry outside along the walls (not sure of the architectural term) to keep the weight of the roof from pushing the wall outward and over."

(M) Perhaps the term is a "flying buttress" (I'm not sure of the spelling)
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[Marcel]

Originally Posted by jahysea

I also started the metal walls today. <snip>
Weather and family fun permitting I should be able to finish all 4 walls and possibly the stringers for the roofing over the long weekend.

I plan to stucco the exterior and use spanish tile on the roof, to match our home.

(M) I made the mistake of framing the entire oven enclosure, including the roof joists and collar ties BEFORE I clad the walls. BIG MISTAKE. I really had trouble screwing the "HardiPlank" s under the eaves because of the pitch.

(M) Cladding your walls before you add your roof, IMHO, will also add significant diagonal bracing and will make the roof easier to work on.

Ciao,

Marcel

[maver]

Originally Posted by jahysea

Not having seen the materials yet, but knowing the sections are only 1' in length, how do they join together? Are they fluted to overlap each other I wonder, or are they straight and I will just mortar them together? If the latter, I suspect they will need additional support, which I can provide as they go through the roof.

They come in both fluted and stacked. Most of the time flu tile is lined on the outside with a brick surround with about 1/2" air gap - this insultation helps the flu tile get hot which helps it draw better.

Originally Posted by jahysea

You are correct in pointing out the force on the outside of the arch walls. Big cathedrals in Europe like the one in Lincoln England have giant extensions with piles of masonry outside along the walls (not sure of the architectural term) to keep the weight of the roof from pushing the wall outward and over.

A buttress is a solid support as you are describing. A flying buttress "flies" - there is an air space below the post that buttresses the wall. Given the thermal expansion issues this might not be appropriate for an oven.

Originally Posted by jahysea

I could easily make a little brick wall on either side of the arch tunnel walls. If I placed it on top of the concrete I just poured I'd be pretty confident they will never move. And nobody would ever see them as they will be inside the walls.

This is what I did. Because it was not visible, I used rubble - left overs from dome construction mortared in place. I was paranoid, so I also placed an angle iron across the front arch and supported it on either side of my rubble to provide additional support.