thomas newcomb wrote:I can't build more than three inches high at a time using hour and a half intervals or it will cave in.
Your mixture is probably too wet and/or doesn't have enough sand.
I am thinking that it will work with cob in the burn tunnel, but it won't last long. An interesting experiment might be to get some refractory powder mix and use that for the cob mix around the hottest areas.
My experience building cob kilns is that I can build up a foot of height without stopping. Your mix must be too wet - you can make it drier as long as a new lump firmly melds with an existing one. More sand might help too, depending on your current consistency. How much straw/dry grass are you using in the mix? That is important for wet strength, and as it burns out it also leaves tiny airspaces which have some insulation value. I would use a low-grass mix on the inner surfaces for dry strength, but as much grass as you can work with around it. I have found that fine dried grass in short pieces (1-2") gives wet strength yet lets the surfaces be smooth, unlike straw. When I mix the dry grass with the clay immediately before use making a very sticky mix, the grass absorbs enough water in a short time to stiffen up the build as I am working. If the walls are thick enough for the exterior to not get very hot in use, the grass may last for some time and act like rebar, making the stove less fragile.
In the absence of milled lumber, you can use anything that can be formed into the correct shape and wrapped in a smooth covering like big leaves. A bundle of crooked twigs on the inside might even leave enough airspace to let a fire burn it out, though I haven't tried that.
Pine needles that I am familiar with definitely do not help - they are too stiff, do not absorb water that well, and break or break down too easily. Leaves also do not help, as they create flat planes where the clay is not sticking to itself, and when the clay dries there is a weak spot.
How thick is the bunchgrass, and how wide are the blades? How long did you cut it? Longer than a few inches makes it harder to work with.
I mix the clay and water first, getting it thoroughly workable and squishy, then sprinkle a handful of grass on it and fold, knead, stretch, etc. Repeat until it is a good consistency - practice! Make sure the grass is not in a clump when you add it, but each blade touches clay.
thomas newcomb wrote:Thanks again for your input. My mix has no grass. I read else where not to use it. I tried using pine nettles but it made more difficult. You are correct I am trying to make this work to become a model. Nicaraguan stoves have no chimneys and the smoky homes cause lung infections in the youth. Last year I brought aluminum rocket stoves made in South Africa and they were a hit. Hence the idea to make them using local materials
How did the aluminum ones work after a year? Are they still being enjoyed? Is the aluminum still in good condiion after one year of rocket-fires?
That cob looks dark, and you should perhaps use less sand if you don't know the clay content. The dry odganic fibers will help hold it together hopefully
You are right. It is too high. This is a temp site. I hoped to build a base when I got one to work. I will let this one dry for 2 days before putting a fire inside it.
I leave for the US on Wednesday. Looks like my demonstrations will have to wait.
Have you seen the adobe/mud cooking stove thread at Donkey's forum?
The rest of that forum has good info too.
thomas newcomb wrote:How do you clean out the ashes? The heat riser is too long to reach into and the channel too narrow.
My burn tunnel is rectangular and I can't reach the back of it because I'm using a J setup. So I got some scrap sheet metal and bent it into an L shape. It has a slight bend in the longer part so it can slide from the feed tube into the burn tunnel. I can just reach the back of the burn tunnel using this and can then scrape the ashes towards the feed tube, then use the shorter part as a ladle of sorts to bring the ashes up.
It does tend to cause ash to fly about, making the cabin get covered with soot over time. I've started using a vacuum and that helps a lot. But if yours are for outdoor cooking then that shouldn't be a problem.
Have a look at this video. I have watched hundreds of rocket stove videos and this seems to be more what you might be looking for. ignore the first few seconds but I am sure you will find the concept helpful
<iframe width="854" height="480" src="https://www.youtube.com/embed/ifpOiCV53FU" frameborder="0" allowfullscreen></iframe>
Is your new rocket stove all dry yet? It will not come up to proper temperature or draft until it is. What is the inside diameter? Is it fairly constant? How smooth is it? You currently have an L-tube, right? That wants a sheet of metal under the stick feed so air can get to the back for best combustion, according to what I have seen. The one L-tube I have built was for an oven, and is 6" diameter with a slightly taller horizontal 20-24" long and a vertical about 30" long, with an exhaust chimney on top of the oven. It burns like crazy without the air channel beneath and consumes the wood completely.
When Ianto Evans was developing a version of rocket stove in (I think) Guatemala for a government agency, they had the same objection, and decided to call it "estufa Rocky", as the Rocky movies were popular then.