Adobe bell stove, Dragon Heater core

I've just finished building a test stove in my yard. It's for evaluating a commercial rocket stove kit, plus a couple ideas of my own..
So far the thing runs beautifully. Here is the photo-intro portion of my thread at The Donkey32 Rocket Stove forum:

In a lot of older houses around here, there are brick pads for putting a wood stove on. Just about every house has one, they have a chimney jack through the roof (or wall) and often the floor has been beefed up below to carry extra weight. I wanted the stove to fit on one of those pads, which tend to be around 4 feet by 3 feet. I have some bricks laying about, so I put together a mock-up pad for everything to fit on. These bricks are pretty big, bigger than standard red-brick.. This pad is a few inches smaller than a 3X4 pad in all directions.



I wanted to build this stove ONLY with stuff I can make or have laying around (plus the Dragon Core), so I made a bunch of adobe bricks. In this stack of bricks there are about 75 bricks, I used a handful more, plus some busted bits and junk from other projects.. When I was drying these bricks, the dog ran through them a few times, some of them got run over with my truck..
I'd say the project took around 80 adobe bricks, measuring 3X6X12 inches, plus a small pile of bits, chunks and halfsies..


First, figuring out how it will all fit. Gotta have a little room around the heater core for insulation, also enough space for the barrel.


It's all stuck together with clay slip and cob.
The clay's from my place. The sand came from our local river, via the aggregate co. and leftover from a different project. The straw was also leftovers.


Here's the cavity for the stove which will double as the "manifold" area, moving exhaust from the bottom of the barrel into the bell.


I want the Dragon core to come back out as clean as possible. This stove is just for testing purposes..
Anyhow, I wrapped the thing up in several layers of newspaper and tape, that should keep the insulation and cob layers from sticking it.


Plop the heater core into it's slot and fill.. I had some rice hulls laying around (all out of pearlite), mixed 'em with clay slip for insulation. Cardboard shields keep the mix from falling into the stove core.


I'm thinking that adobes that are stuck in with cob will be easier to take out than a solid cob top.. Maybe make taking it apart easier, so custom bricks.


Finishing touches on seating the barrel and the manifold area.. The barrel is a little bit too tight for my liking, it's nice to have ample room to really seal in the barrel and make it sturdy. As a test, this will be fine; on a permanent installation, I'd want to add a couple-three-or-so inches to that area (closer to my 4 foot limit over all).


Heat riser. The Dragon Heater, vermiculite-board heat riser. I haven't yet added any more insulation to it; I may yet do it but I'm putting that off for now. I'll use it as-is for a little while first.
You cans see that the barrel has been "cheated" way over.. It took a little shuffling to make everything fit; anyway, it's better this way (for now)


All assembled!



It's a 6 inch Dragon heater core and a 30 gallon barrel (29 inches tall, 18 inches diameter).
Barrel top gap is around 5 inches.
The bell (all measurements are taken on internal surfaces) measures 13 inches by 26 inches by 36 1/2 inches. The top is corbeled, so there is a funny little pop-up to consider for ISA measurements, it's 3 inches (brick thickness) tall, 7 1/2 inches wide and 20 inches long.
The stove-pipe is 5 inch diameter.

Kirk; Thanks for sharing !! This looks awsome. Can't wait to hear more about it.

What's the update on this?

Love the idea. Have been thinking about making a Dragon Heater "Castle" build out of cob brick for the bells, as the flue liners are hard to come by and expensive out in my area.

How's it working? How long does it retain heat after a fire?

Thanks
Von

Love the photos, thanks for sharing them. I live in the uk where cob buildings go back to the seventh century still partly stand. I do some cob repair work and one technique is to bury steel wire in channels cut under the surface of the cob. If your stove shrinks and cracks, do you intend to fill the cracks, leave them to open and close as heat dictates or fill and stitch across them? I love the idea of cob blocks to build a stove, particularly as you can corbel them. Did you think maybe you could build an arch or use a former left inside to burn away? Thanks again for sharing those photos, really interesting.

Frank Blaker wrote:Love the photos, thanks for sharing them. I live in the uk where cob buildings go back to the seventh century still partly stand. I do some cob repair work and one technique is to bury steel wire in channels cut under the surface of the cob. If your stove shrinks and cracks, do you intend to fill the cracks, leave them to open and close as heat dictates or fill and stitch across them? I love the idea of cob blocks to build a stove, particularly as you can corbel them. Did you think maybe you could build an arch or use a former left inside to burn away? Thanks again for sharing those photos, really interesting.

What does the wire do?? I'd think that wire in the walls would make a cold, condensation point within the walls..

This stove was just a test model in the yard. I've since broken it up and re-used all the materials. I've noticed that where an all cob/adobe stove cracks most is at a connection between cob and other materials. I will just let the seams expand and contract on their own in that case.. If cob cracks on it's own for some reason, usually during drying, I'll just cover it over with a good plaster and be done.
Arches will work just fine, I doubt seriously that it would get hot enough to burn a former inside of the bell, nor would there be enough oxygen to support combustion.

Hi,
I use metal straps to reinforce loose laid bricks in kiln building, where thermal ranges cause a lot of movement in the structure. I wondered if wire to reinforce at hot spot to colder spot transition points would ease the possible problems of cracks. I totaly take the point about condensation, maybe warm cob can assimilate it, transfer it to the surface and dry it out through evaporation. Kiko Denzer advises that a clay oven can do this when moisture from food being cooked can threaten to soften an adobe oven roof. I saw so many possibilities for smooth rounded cob shapes in your idea that left me thinking, any arch other than a catenary arch puts outward pressure on its supporting walls, so some sort of bracing pulling the walls inwards can be needed in a minimal structure. I also got to reading ianto Evans book where he says the square corners help promote turbulance, aiding the mix of oxygen and hot unburnt gas. This seems to say the blocky, corbelled roof is better than rounded or arched shapes.
I love the idea of cob blocks as I find I can think designs through when I can play in 3d.
Would you use clay and sawdust or perlite mixes for some of the blocks? What would you think of blocks with a layer of this mix say 2 inches thick added at the block making stage?

Frank Blaker wrote:Hi,
I use metal straps to reinforce loose laid bricks in kiln building, where thermal ranges cause a lot of movement in the structure. I wondered if wire to reinforce at hot spot to colder spot transition points would ease the possible problems of cracks. I totaly take the point about condensation, maybe warm cob can assimilate it, transfer it to the surface and dry it out through evaporation. Kiko Denzer advises that a clay oven can do this when moisture from food being cooked can threaten to soften an adobe oven roof. I saw so many possibilities for smooth rounded cob shapes in your idea that left me thinking, any arch other than a catenary arch puts outward pressure on its supporting walls, so some sort of bracing pulling the walls inwards can be needed in a minimal structure. I also got to reading ianto Evans book where he says the square corners help promote turbulance, aiding the mix of oxygen and hot unburnt gas. This seems to say the blocky, corbelled roof is better than rounded or arched shapes.
I love the idea of cob blocks as I find I can think designs through when I can play in 3d.
Would you use clay and sawdust or perlite mixes for some of the blocks? What would you think of blocks with a layer of this mix say 2 inches thick added at the block making stage?

I see your point with the arches. My tactic would be ample buttressing for the arch to lean on. My concern with metals in the cob under heat is differential expansion, which CAN crack up the cob. On the other hand, bells don't really get that hot, it might not be a problem.
The square corner thing is about the combustion area. Square corners improve turbulence for fuel/air mixing. After the burn, it really doesn't matter what shape you got. Insulation needs to be in the burn area, everything else should be thermal mass; sawdust, perlite, and all that are insulation, and could be around the combustion unit but not in the bell or anything else. Check out the construction sequence again, where the stove needed insulation it got it, everything else is thermal mass and COULD be much heavier in the sand department.

Thanks for the thoughts. How did the vermiculite board fare? It looks like a good riser.

Regards


Frank

Frank Blaker wrote:Thanks for the thoughts. How did the vermiculite board fare? It looks like a good riser.

Regards


Frank

So far so good. The thing works like a charm and I like how little space that riser takes up, leaves LOTS of room inside that barrel.
I have NO idea how it will do in the long run.

How did that board riser hold up in the long run?