dmun's 36" geodesic oven

[PizzaMan]

Good looking oven, and a pleasure to follow the posts. I have been watching for a while.

I don't mean to be a critic, but I would encourage you to carefully evaluate before enclosing the oven: A critical issue in masonary construction--of any type--is to avoid running faults or on-going lines from one row of material to the next. (I'm sure someone could explain this better than I.)

I constructed my Pompeii with little difficulty, but when I first fired it I found I made a mistake: about three of my cut bricks lined up to the degree that they shifted slightly, creating a small crack. It is nothing that will affect usage, and has not grown with use. But I was disappointed to see it shift somewhat.

As I look at our photos, it is apparent that you have "broken" all the masonary rules regarding runnng seams. I hope that I am mistaken, but I would be concerned that your hard work and ingenuity may work a little bit against you. At least consult with someone with more experience than me, and bring up to temp very, very slowly. Again, the engineering is great, except that the hexoganal pieces are actually several pieces, each with faults (where edges meet). It may not hold as well as one would hope.

Perhaps this is not an issue. But there are enough qualified builders here to offer some good feedback on this issue.

Best of luck and thanks for letting us watch!

Michael
aka PizzaMan

[dmun]

running seams

The picture you reproduced really shows that: an uninterupted mortar line crossing the entire oven. In fact the entire dome is an interwoven mesh of running seams.

Will it crack? Cracking is certainly a issue with homemade dome ovens. I remember one post here entitled "Enough with the cracking already" It's my hope that having closely fitted seams, and refractory mortar matched to the expansion of the firebrick will reduce or eliminate cracking. You just never know. Fio had a piece of refractory flue tile crack on him: You should be able to drop that stuff off a roof.

One precaution i'm going to take is have a slip plane between the door opening and the refractory assembly within, to avoid differential expansion. Another is to let it cure for a really long time: Because I'm building a two story, two flue masonry chimney, it will probably be next spring before I have it properly vented and build a fire in it.

Thanks for your concern. It's one I share.

[DrakeRemoray]

I have a big piece of matching slate for that:
I know, not the best material, subject to staining, but it's here, and will complement the rustic look of the oven.

Sounds great. We don't call that staining...we call that "patina".

Drake

[dmun]

Good weather

We had a stretch of great weather this week, so I took the time to go back to masonry.



First the slate. The big piece of slate that I had gotten to make my oven landing shelf cracked all the way through while being cut. Zut alors. I went to the stone yard and got a 12 x 48 bluestone step, and had them cut it down to the 40 inch width. Not cheap to buy, but the cut was free. I also got another little piece of the same material to make the arch pieces, since many of the arch stones I tried to make were fracturing when sawing. The piece in the center was sound, the original darker color, while the blocks on the sides match the shelf. It's a polychrome extravaganza. You'll be glad I passed up those bright pink marble tiles that HD has on sale for a buck apiece.



Here's the refractory inner arch pieces, cut to fit form,



and mortared together into a pre-fab arch.

[dmun]

flue funnel

Once on this forum, I saw a picture that someone posted of two flue tiles side by side sitting on top of the oven opening. They may just have had them stored there, but it gave me an idea:


If you cut an 8 x 12 flue tile on the bias, as drawn, you get,



Two pieces like this, which,



can be trimmed like this,



and assembled into a thing like this. It fits an 8 x 8 flue tile on top, and flares to 8 x 15 1/2 on the bottom. Cool, huh? Stay away from those pricy sheet metal fabricators. Warning, refractory flue tile is the hardest thing I've cut so far on this project, and the size of the thing means that the long cuts need to be made with a diamond blade in the angle grinder.

[dmun]

arch assembly

The pre-fabricated refractory arch is mortared to the ends of the flared entry walls,



But not to the decorative walls in front. The whole refractory oven assembly is designed to float free of the outer walls.



The gap between the refractory and decorative arches is going to be filled with mortar, so I don't get smoke leaks at the arch, but the inner arch is wrapped with aluminum foil to prevent the mortar from adhering the two together.



I had filled the gap between the flared entry walls and the exterior walls by mortaring in some triangle scraps of firebrick:

[dmun]

outer arch

I start to build the outer arch:



The exaggerated keystone in:



A rear view:

[dmun]

exterior done for winter

In our spell of warm weather I got the oven up to the point where it's above the level of the hole I knocked in the exterior wall, so I can put up a temporary roof to close the workshop up for the winter. Some pictures with the forms removed, and the stone scrubbed:

[james]

Wow.

Is that the coolest thing, or what. That beats Nick's assistants -- well, maybe.

David, are you thinking about a mortar coating to help hold those joint together through thermal expansion and contraction, or are you going to rely on the "mesh of interconnected seams" theory.

I am picturing a low and slow oven curing process before the enclosure is closed in, and even before insulating blanket goes on.

James

[maver]

David, that really looks great - very professional, the slate/brick design fits together very nicely.

David how high is your oven opening relative to dome height?

James - does cladding provide stability for the dome joints? Shouldn't the similar thermal properties of the refractory mortar and firebrick align in a well constructed dome as David's appears to be (with very tight joints)? Thes refractory materials shrink with heat, right?

[dmun]

David how high is your oven opening relative to dome height?

The dome height is 18 1/4, the door height is 13 1/4, the door width at the bottom is 18 1/4. Those are all one quarter inch bigger than planned, mortar creep no doubt.

James - does cladding provide stability for the dome joints? Shouldn't the similar thermal properties of the refractory mortar and firebrick align in a well constructed dome as David's appears to be (with very tight joints)? Thes refractory materials shrink with heat, right?

I'm not too woried about the stability of the thing: there's not much mortar, and it's closely matched to the linear expansion of the firebrick. I've been careful to create slip planes between firebrick and other materials, and the exterior part of the masonry chimney will be independantly supported from the firebrick liner. I notice that when I hit the dome, it rings like a bell, sort of. I think it's really sound.

Just as a side note, when I set the inner, refractory, arch, I used the last of my original fifty pound bag of Heat-stop refractory mortar. Not too bad for an oven, an entry, a fireplace, and a rumford throat. On the other hand I just bought my third ten inch tile saw blade.

[christo]

Brickie

Still using and liking the Brickie?

[dmun]

Bricky

Still using and liking the Brickie?

The Bricky system is great, and it would be even better if I were building a freestanding oven, because one of the things it doesn't do is lay a line of mortar up to an obstruction. Using the bricky emphasizes that you are not gluing bricks or blocks together with mud, but that you are building concrete objects to fit between your masonry units. Everything that comes with the Bricky is great. The round nose trowel is perfect for mixing, moving, and applying mortar. The jigs for applying mortar to the end of bricks and 4" blocks make the worst part of the job easy. Once you are used to using the pointing tool, it lets you finish the joints smoothly. (You use it twice, once to push the mortar in place when it's wet, and again to smooth things out when it's a bit dryer.) Even the video is useful: it shows you techniques that masons learn by seeing someone else do it. Do you know you pick up mortar with the bottom of the trowel? The only thing I haven't used is what they call the mason's mate, a string guide for long walls.

If I were building a freestanding oven, I'd make an exterior wall of brick and and interior wall of half thickness blocks inside the wood storage area separated by a half-brick (4") space. The inner blocks could support the hearth slab , and the outer wall be most of the form for same. All I can say of the Bricky is that it makes bad bricklayers good, and good ones fast.

[james]

There is a lot to like about the enclosure design -- the oven construction aside. I agree that the slate and brick work well together, and the repeating arch, both in material and curvature with the oven opening and the storage area below looks nice. The slate baseboards on the foundation corners looks very nice. I like the cantilevered landing (I am coming to like that design), and the slate threshhold into the storage area is clean and elegant. And I like the larger keystone at the top center of the oven arch. All really nice. Great conception, great details, great execution.

Maver, on the oven itself, if David can build the dome to +/- 1/4" from his origional cad drawings, I am just going to sit back and watch it go up. Like a fine Swiss watch. We will all await the first firings with anticipation -- and see how she cooks!

James

[dmun]

closing for the winter

We've had an amazing run of great weather these past few weeks, but it's time to close up the workshop for the winter with more than a draped tarp. I have to heat this space, after all. I started by filling the old window hole with glass blocks I picked up from an eBay vendor. You'll notice they didn't quite fit, so I had room for a slate sill to match the one under the wood storage door.



This dark inside view doesn't show much, but you can see that the rustic slate sill is deep enough to cover the edge of the concrete blocks. I'll finish the top and sides of the exposed block with concrete.



As a side note, glass block aren't easy to lay. They are matted on the edge, but the mortar doesn't really stick to them. Since they are not porous like masonry, the mortar doesn't have that initial set up within a few minutes. The whole thing stays wobbly until the mortar sets up by itself. Also, since light shines through, every slight difference in mortar thickness is really obvious. On the other hand, it's really easy to clean the mortar off them, and you have to because it slides all over the surface when you are trying to get them in place.