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Using cow dung as the mass for a rocket mass heater

 
Charles Laferriere
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Location: Quebec, Canada - 4b/5a
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Hey folks!

Winter is coming up here, and I've been considering to build a rocket stove in the unfinished basement.

I have a cow, and therefore, a lot of cow dung.
In India, they make bricks and build houses with cow dung. I played around with it, and it seems like a fine medium. Odorless when dried.

I was wondering if it could be a good medium, perhaps mixed with some pre-mix cement? to build and mold the mass around the rocket stove, of course...

Any thoughts?
I've never heard of anyone doing that... but sounds legit to me.

Charles
 
Charles Laferriere
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Location: Quebec, Canada - 4b/5a
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Main reason behind that is cost, ressource availability and the complete lack of clay in the area.
 
Tobias Ber
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hey charles...

it s awesome to talk about shit so freely.

i think that cow dung will be insulating. it contains lots of chewed plant fibres. for the mass you would not want insulation.
as far as i remember, (fresh) cow dung can be used in cob building to harden or waterproof the surfaces. so it could be helpfull for the outer layer of a cob-bench.

when you ve got a lack of clay, have you looked into the pebble-style thermal-mass-bank? (Edit: https://permies.com/t/48515/pebble-style-rmh-fisher-price )

for "cobbing" aroun the core, there must be recipes that are not insulating.


good luck
 
Glenn Herbert
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"Complete lack of clay" - where are you in Quebec that there is no clay in the area? I would think there is someplace within a reasonable drive at least that you could harvest several buckets of clay. If you talk to a highway department or a building contractor, they will know where there is clay.

You can use mostly rocks for the mass, as long as you have enough clay or similar to fill the gaps between them and the duct.
 
Charles Laferriere
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Yes, of course I could use rocks. But I *want* to use cow dung.
I didn't go through books... only one workshop.. I don't see how cow dung mixed with some sand and a pinch of premix cement wouldn't make a good mass?

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Charles Laferriere
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Glenn Herbert wrote:"Complete lack of clay" - where are you in Quebec that there is no clay in the area? I would think there is someplace within a reasonable drive at least that you could harvest several buckets of clay. If you talk to a highway department or a building contractor, they will know where there is clay.

You can use mostly rocks for the mass, as long as you have enough clay or similar to fill the gaps between them and the duct.


I'm 30 minutes by car south of st lawrence river.
10 inches of topsoil, then it's sand.
 
Tobias Ber
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sand+dung+cement looks like soilcement with fibres. what ratio do you think about?

you should test that mixture, it might not be hard enough and crumble when you use the bench.

you COULD make a casing for the bench. maybe bricks and mortar. fill that with soilcement (maybe + rocks) and add a solid surface ontop.
 
John McDoodle
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I say if you can dream it, you can do it.   I've recently poured a soul cement pad/step out front of my place.   I mixed in earth and some organic fibers got in there, I used about 1 part cement and 3.5 parts soil.   There are 6000 psi cements that already have fiber in them, and same with cob, it is usually made with organic fiber like straw.   Once you dry it and mix it well, and don't use an excess amount in sure sit will mix and harden.   If they use it in cob sometimes, I don't see why not.    However it would absolutely need to be dried and mixed well with sand and cement to avoid health problems and bacteria and decomposition.    Just try it.   A bag of cement is only 5$, so make a test brick or something and see how it dries and lasts and hardens.  If you can turn waste into a building material, you are winning in recycling and permaculture
 
Charles Laferriere
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Well I've read quite a bit on india sources about cows and I ended up being quite converted to the whole cow thing.
Apparently it is good at absorbing radiation

I guess I would fall more into the category of the health/wise usage of resource nut?

I'm extremely stressed right now as my cow went through the gate and it's a cold night.
Can't find her.
My throat is tight.
 
Charles Laferriere
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I'll make experiments and post results.
 
R Ranson
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I think this is a great idea.

Cow dung has a long history of being used in construction, Asia, North Africa, all the way through to North Western Europe.  Wattle and daub is the most common uses of manure in construction in Europe, but it's also sometimes used in cob.  Some of these houses are still standing and in use hundreds of years later.  Some are over a thousand years old.  It is my understanding that once dry, any parasites or bacteria that might possibly be harmful to humans would be nullified. 

I've seen references to dung being used in oven construction mixed into the cob - but I can't find the source and I can't remember the outcome. 


I'll make experiments and post results.


Please do!

This is the only way you'll know for sure.  Please let us know how it goes.
As with any group of people, we are all working with different locations, different materials, and have different biases that could taint our opinion of working with dung.

Also, I feel your pain with the lack of clay.  Where I live, our clay is about 20 feet down, far too deep.  I don't like the idea of gathering clay from public land as it is a finite resource and I worry about ecological damage in a protected area like a park.  Also, not exactly legal in some places.


By the way, did you find your cow?  Hope she's okay.
 
Charles Laferriere
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Ah! Yes she came back to her shed during the night. First fence built, I couldn't understand why the electricity wouldn't work.. I had wrapped the wire around each nail which went through the insulator, so the wire was grounded with each nail. Now it should be good, but damn, she's got an attitude of her own!

I plan to make it my bed. Warm bed, made with cow dung.

What more can you ask, really?
 
William Bronson
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I am going to suggest you space your rocket off of the basement floor.
An air space will help prevent the heat from being sucked away into the ground.
Often people will build on cement board supported with bricks.
On the floor beneath a layer of aluminum foil is placed with the shiny side up,to reflect heat radiating from the mass.

The other thing I suggest is building a batch box rocket,since it will be located in the basement,away from the living areas. Batch box rockets need less tending.
 
Joseph Lofthouse
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Organic matter surrounding a chimney is likely to off-gas. It may start on fire.

 
Michael Cox
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Like Joseph, my instinctive reaction is that the heat of a fire, and a large amount of organic material in close proximity = recipe for disaster.

Secondly, I don't think it will work quite as well as you hope. Most of the mass of cow dung is water. As the dung dries it will end up quite light and porous - it will effectively insulate your heater, rather than act as a good heat store. For a "mass heater" to work you need "mass". Rock is great, cob works well because it is nearly as dense as rock. Blending sand with your dung may help to some extent.
 
Charles Laferriere
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All very good points to be taken into consideration.

Thanks for the interventions.
 
R Ranson
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Last night, I was chatting with someone who's father was a bricklayer who specialized in fireplaces, coppers (big boiling pot for doing laundry - but also refers to the brick stove that the fire is made in to heat it) and other similar constructions.  Apparently, they sometimes used manure to help line the chimney... although the details of this are lost.  I'm assuming it's mixed in with other things, but maybe not.  It was mostly horse manure but sometimes cow. 


I think there is something worth experimenting with here.  There are a lot of historical examples of dung being used... both as fuel and as construction material.  Maybe some more research and some small (and safe - we are talking fire here) experiments would be the next step?  I'm really curious if this can work.

I'm also thinking that rocket mass heaters are somewhat different than regular fireplaces.  There may not be a historical president for this kind of thing, which would make understanding the details of how a rocket mass heater works, even more important.  Have you seen Paul's recent videos yet?  https://permies.com/t/60211/Building-Cob-Style-Rocket-Mass
 
Glenn Herbert
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Dung makes an excellent binder for cob, as much of it is short fibers with the easily degradable parts stripped off, but as far as I know it is generally used as a component along with clay and sand, not as the entire mix.

Consider a well-weathered and dried cow pattie - it is quite light, not what makes mass at all, but an insulator as mentioned by Michael. Essentially all of a cow pattie is organic, and thus will char and burn if it gets hot enough. Large parts of the mass, especially internally, will get that hot and sooner or later will burn.

For the base, I concur with William Bronson. The one thing I would change is to put the aluminum foil on top of the bricks, shiny side down. The foil gets its insulative quality entirely from the shiny metallic surface's resistance to radiation in or out, and a dusty surface loses that shiny quality.
 
Charles Laferriere
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YIPPIE!

As I was doing rounds of roots harvest on the property... I've found a pit of pure clay!!! So I've got sand, clay and high quality soil. OHhhh boy am I a lucky one or what. And 5 months winters, too.

So.

I've been experimenting with:

1 part clay
1 part sand
1/2 part dung
1/8 premix cement


Looks good so far, easy to work with.
It doesn't dry up yet ironically... because it's too cold and damp.
I'll be able to turn the baby up within a week.

Now for the story-level bench.


I was thinking to fill the bench with perlite? then cover with cob. With a wodden frame structure, and double vent pipe going through the bench.

Your inputs are always very valuable and appreciated.
 
Glenn Herbert
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Hurray for the clay!

But NO perlite in the bench, unless it is at the bottom or against an exterior wall where you want insulation. Use solid cob, with plenty of rocks embedded if you have them to increase the mass and reduce the amount of cob you have to mix.
 
Charles Laferriere
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Ah! May I ask why?

Not even mixed into the cob?
 
Tobias Ber
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charles... you want to soak the warmth into the mass. any kind of insulation there will hinder that, so more warmth would go through the chimney.

in mass you want stuff that soaks up and hold the warmth well.

but insulation between mass and an outside wall or a floor is a good thing, because it hinders the warmth leaving the mass that way.
 
Charles Laferriere
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Oh right.

Of course perlite does that.



Thanks..
 
Rebecca Norman
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Well, I live in India and can speak of cow dung. In a dry climate, it dries very hard and tough, and is a good addition to cob or earthen plaster etc. It doesn't smell at all when dry. But Quebec is not dry like where I am.  But as mentioned above, it's very light and in fact, on our buildings, we consider it an insulating material. Whereas, for the bench of a rocket mass heater, you want something with more thermal mass, and not as insulating.

I would very much recommend that you NOT add even a little bit of cement to your mix. This way, if you decide to replace the thing after a few years, it will be a nice compostable material. If it has a little cement mixed in, it will be weird construction waste that isn't strong enough to use as "urbanite" but isn't just soil that you can add back into your landscape. If it's made only of soil, sand, clay, and/or cow dung, it can be added back to and become healthy soil.

As a fuel, dried cow dung gives a pleasant sweet smoke that I find similar to apple wood smoke.
 
Charles Laferriere
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*sigh*

I live in a such a barbarian land.

Thanks Rebecca.
 
Tobias Ber
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i saw in a video (was it the wisners?) that they used horse manure in the finish-cob-layer of their bench. the purpose is to give a more resitant surface.
 
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