Sap Warmer Rocket Stove made from Ash and Clay

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Re: Sap Warmer Stove

Postby michaelegan » Fri Jan 23, 2015 4:33 pm

Truly impressive work! So, to get me up to speed on your recipe and theory, you have eliminated sand, furnace cement and fibers (rock wool, etc) for ash and straw/grass?
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Re: Sap Warmer Stove

Postby michaelegan » Fri Jan 23, 2015 4:38 pm

more questions: can you describe the qualities of the mix once it is fired? Is it more dense than Matt's original cast core? Would you want to surround the core with more insulative material? If I build a riser from #10 cans will the riser hold together after the cans burn out (which will probably be quickly)? Thanks again for posting your work and progress
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Re: Sap Warmer Stove

Postby hpmer » Fri Jan 23, 2015 6:02 pm

I can't compare this to Matt's mix as I have never built with it, but maybe Manny can weigh in as I think he now has. I'm sure there is a bit of sand in the clay subsoil, but i don't add any extra myself. It is straight clay subsoil (minus the rocks and roots that I screen out) mixed with ash along with the dried ornamental grass leaves.

I'm still drying out this stove version so don't have conclusions on this ratio yet (I hope to by this weekend), but my original 8" stove that is 1:1 Ash:Clay fired hard like a lightweight concrete. It is housed in a metal framework so it doesn't get abused much. The feed holds up very well although I try to be careful when adding wood. I didn't add anymore insulation around it. The process is building an inner and outer form and packing the mix between the two. I'll post some pictures of the 8 incher so you can see it, but it is basically a one piece "J" stove that's probably 40" tall. I didn't build it in two sections like Matt recommends. It's pretty heavy but I can move it around with a hand truck.

The original stove needed patching after the first few burns to fill voids left after firing. Some of it fell out, some disappeared, but I haven't had to patch it for quite a while now. And I just patched it with more of the same 1:1 mix, wetting the original walls down well before applying and it fused to the original stuff quite well. Overall, I am very happy with the original mix and am looking forward to see how the 5:1 holds up.

Your cans won't hold up for long, but don't really need to. Really only to let the mix set up. I mix mine pretty wet so it can sag a bit if not contained. But after it has dried a bit it is fine. Certainly after it is fired and the cans are consumed the stove body will hold up just fine (again speaking to the original 1:1 mix here).

I'd suggest making some test pucks with different ratios to see what holds up after firing for you. Manny has commented that in his African stoves he can't go much beyond 1:1 or it gets too crumbly. So it seems to depend on the qualities of your materials.
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Re: Sap Warmer Stove

Postby mannytheseacow » Fri Jan 23, 2015 6:24 pm

I've never done any density tests but what I am using seems to perform just as well as Matt's mix in the forms that I have tried it. To be fair, apples to apples, though. When I've made Matt's mix, I'm using zonolite because that is what is available for me. That said, I have no idea any details about this clay we are digging from the dry river here but it is extremely pure, gray, and is really fantastic stuff. I wish I had clay like this back home.

We have been sticking to 10 cm of insulation around our cores and no heat is transpiring through to the forms whatsoever. I even made an 8" J a couple of days ago and cranked that thing really hard for several hours before pulling the forms. I picked 10 cm more because 10 is an even number the locals can remember, even though it is close to the 4" that is recommended, but what I am seeing is a really good insulator; again the details are probably in the mineral content of the materials we are using.
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Re: Sap Warmer Stove

Postby michaelegan » Fri Jan 23, 2015 7:48 pm

Thanks hpmer and manny. Manny, when you say you're packing the core with 10cm of insulation are you using ash for insulation?
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Re: Sap Warmer Rocket Stove made from Ash and Clay

Postby mannytheseacow » Sat Jan 24, 2015 2:52 pm

Yes, 1:1 clay:ash mix.
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Re: Sap Warmer Rocket Stove made from Ash and Clay

Postby hpmer » Mon Jan 26, 2015 2:14 pm

Stove is now in the drying phase. Notice the line where I started with the increase of grass in the mix:

Image

And a close up. Lot's of voids that I'll be covering with a thin layer of probably 1:1 mix on the outside for durability once it dries:

Image

A 4" feed tube feeding a 6" riser:

Image

I wanted the 4" feed can to be flush with the outside which made it entirely too long on the inside, but I figured it would burn away soon enough. I cut a slice on the top side inside the riser but there is still way too much blockage to work well. Between the cold wet mass of the stove and the merely inch or so from end of the feeder can to far wall of the riser, there is not enough fire produced to make the heat to eat the can away fast enough. And, I can't get tin snips in to cut it away very well. Oh well, lesson learned. Next time I'll either build the form from wood (my preference anyway) or slice up the can where it protrudes into the riser. Another few hours of burning should resolve that issue.

Still amazed at how clean it burns even with the above issues. I think this is going to be a nice addition to the arsenal.

I am seeing first hand what you guys with benches talk about when "driving water from the stove." I burned it last weekend and it steamed pretty good for about 4 hours. Then it sat inside for a week. This weekend I fired it for another 3 hours and it steamed more and water started dripping from the bottom after it heated for a half hour or so.

Pretty happy with it so far, but still way too heavy to move around easily. I suspect that will change once I get rid of all the water weight.
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Re: Sap Warmer Rocket Stove made from Ash and Clay

Postby hpmer » Mon Jan 26, 2015 2:26 pm

Here's a shot of a different stove I promised to michaelegan showing my main 8" stove. I built it inside a framework of HVAC ducting. It's a beast. I can move it around using a hand truck, but I only moved it once into position. Certainly not intended to be portable.

Image
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Re: Sap Warmer Rocket Stove made from Ash and Clay

Postby pa_friendly_guy » Mon Jan 26, 2015 3:06 pm

That looks great hpmer. How does the 4" pipe going into a 6' riser seem to work for you. Does it reduce the rocket effect, does it let the flames go up the raiser a lesser distance, does it allow more air to mix in and create a better burn? Just wondered if you noticed much or any effect on the burn. As a suggestion, maybe you can go into the top of the riser with a heavy small metal hook and try to pry the back of the 4" can up and out of the way to open it up a bit and speed up the process of it burning away. Just a thought, ;)
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Re: Sap Warmer Rocket Stove made from Ash and Clay

Postby hpmer » Mon Jan 26, 2015 3:27 pm

The 4" into 6" is a concept I tried with great success on another stove some years ago. I think it works well because it lets less air in, rather than more. Think of it as permanently choked down. But, since I rarely ever run it full out, less air seems like a good design component. And even with the above issues, I'm getting flames to and above the top of the stove now so flames will certainly lick the pot when in use.

I made some char cloth on it this weekend while drying it out. This batch just heated for a couple of hours and never did get the smoke poring out of the center hole of the cans so I certainly wasn't getting an abundance of heat. Haven't tested it but looked good when I took it off.

Thanks for the suggestion on the hook. I haven't wanted to mess around too much and end up messing up the core when just a little more patience will solve the issue by itself. I've tried pulling on the can walls to deform them and that worked a little. But one more burn session should mostly solve the issue and then I can really see what the potential of this thing is.

The mix does smell a bit as it dries out and it's not a flavor I want mixed in with the maple syrup when I get to that, so a few more weekend burns and I should be in good shape.
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