A Mud Batch-Box

[Deleted]

Sept 19, 2013 20:48:21 GMT -8 Donkey said:

Ermm.. the only issue with lowering the throat is that a simple plate for the p-channel will not do.

Can be done with a second smaller plate.
Just make space for this plate in the form.

[Donkey]

Yep.. I was also thinking about a little mud channel.

[dvawolk]

Sept 19, 2013 9:13:31 GMT -8 peterberg said:

I'm not sure whether it is important or not. One thing though, this burner yields its highest efficiency when the fuel is level with the ceiling of the port or higher. As a consequence, you have to load your stove right up to the top to achieve the same effect.

Peter,i think I have seen something similar on that Netherlands batcbox bell stove: there was some metal floor in the middle height of batcbox and on to of it some wood pieces burning. The fire had to go down under that metal floor (with gaps) to reach the heatriser. Can one achieve higher efficiency with half filled batcbox in this manner?

[dvawolk]

Got the thread, it is the second video:
donkey32.proboards.com/thread/767

[peterberg]

Klemen,
That's an experimental stove, half batch box and half downdraft gasifier. Somebody else built that and I did some testruns on it but it wasn't any better than the pure batch box, rather the contrary. But it did look quite nice!

[gavinguy]

donkey, any updates? I'm building a 4.2" system right now using clay, fireclay and perlite, so i'd be very interested in your results.

i'm particularly interested in making the batch box shorter and wider (more like a 2:2 ratio instead of a 2:3 ratio). this is because it will be forming the base of a cookstove and with a 4.2" system my riser has to be 30".

[talltuk]

Yeah I am really interested as well as fancied trying a cob bathbox for my shed heater when I get to it

[independentenergy]

Oct 8, 2013 23:34:34 GMT -8 dvawolk said:

Got the thread, it is the second video:
donkey32.proboards.com/thread/767

this video is very interesting

[4seasons]

Any updates on this? How well did it hold up? Also curious if you have any idea what the clay/sand/ash ratio of the mix you used. I am currently building my prototype using very similar ingredients.

[Donkey]

I didn't give it the testing time that it deserved. Life did it's thing and I've been off to other projects.
I needed to alter the throat a little, drop it down and change the way the p-channel worked. Instead, it's been sitting in a corner of my shop, patiently awaiting my return.. Occasionally, it looks at me with a forlorn expression and I feel a pang of guilt..
I plan to dust it of and play with it again at some point this summer but I'm not really sure when I'll have the time.

[Esteban Campestre Abejil]

I am very interested in this small, rustic stove. I'm planning to build one now and my budget is limited. I have almost all locally available materials needed, but still need to be sure that no collapse after a month of use. Anyway, I would love to try it, because we leave in late 2015 to move to another area of ​​the country. We would be happy if it lasted until then.

I'm looking forward to this experiment.

Esteban.

[DCish]

I'm planning an outdoor build in Sept... have any experiences since this stove led to changes in the recipe /mix that you used here?

[Daryl]

Feb 23, 2014 10:38:02 GMT -8 4seasons said:

Any updates on this? How well did it hold up? Also curious if you have any idea what the clay/sand/ash ratio of the mix you used. I am currently building my prototype using very similar ingredients.

I am also curious as to the clay/sand/ash ratio used for mud batch boxes. I want to try it in the future and I know someone off site I would like to relay the info to as well.  Both of us have an interest in experimenting with building clay stoves including possibly mixing in pieces of pottery clay and firebrick.

[Donkey]

Clays are different from place to place. My soils will be COMPLETELY different than yours and so I won't actually be doing you any favors by giving you my recipe. It WILL be helpful for me to share my methods. I've posted this in other places, but it hurts nothing to put it here as well:

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This is for people who plan to use natural materials to cast (or build) rocket stove parts, rocket stoves and/or earthen ovens. These materials can be used in SO many places, it's worth knowing this stuff even if you never build a rocket stove (or oven). This is for higher temperature applications.
For reference, I've developed this approach, using natural clay-rich soils that can be dug up on my land and/or locally, near to me. Your particular soils will have different properties and requirements, so mixes will vary. None of what I've laid out here should be seen as a hard-and-fast recipe. ALWAYS test rigorously, NEVER assume that my proportions will just work for you.

I think that what is generally needed are 3 different kinds of mix, though they will be made of the same basic materials, the different mixes will perform different functions. You will need a hard material for places where it will experience abuse (the feed area), banging wood, fire poker, etc; a softer material that provides resilience to heat and better insulation but does not need to resist physical banging; finally, you need a "plaster" material for sealing porous surfaces, smoothing over shapes, patching dings and other odd jobs.

First, prep the basic materials:
Make clay slip and screen out the rocks, roots and other junk. Basic Slip should have the consistency of a heavy-duty milk shake with just-melted ice cream. Dip your hand into the slip, it should come out looking like a thick rubber glove of mud. I toss raw dirt into a barrel, add water, mix with a drill motor/paddle mixer and then screen it into another barrel.
Wood ash should be screened as well. I crush in sintered ash along with the powdery stuff and rub it through the screen. I think the sinter makes good aggregate.
Remember when screening, the size of the screen you use is rather important. It's a big factor in determining the size of your mortar joints and things like that. Smaller screens make for harder work getting the stuff through, but big grained materials can be a total pain in the neck for some uses (mortar joints should be as thin as possible). Learn to know when you need a smaller screen but work with the biggest one you can.
You will need a chopped fiber, I toss rice straw through a chipper/shredder, it makes a nice 1/4 inch minus fluff. Alternately you could use rice hulls, horse manure, maybe pine needles or something similar. The fiber (closest to big heat) will mostly just char away, either way it really helps with workability, prevents cracking, etc.
You generally want sand that does NOT have a crystalline structure, crystals tend to expand differentially when heated, expanding along an axis, breaking the clay and crumbling the mix (There are exceptions to every rule). Ideally, your sand should include as many different sizes of grit as possible and be rough/crushed rather than round/polished.
I've heard people say to only use the construction grade perlite, which is coated to keep out moisture; agricultural perlite will hold in moisture and is missing the coating. My experience is that the only difference between the two is that the uncoated perlite takes longer to dry out completely.

The key note of all of my mixes here are going to be wood-ash/clay, so the basic mix:
Mix together the slip and ash, adding (by degrees) dry into wet until it gets difficult to add more ash; it often resembles a heavy, well floured bread dough. To this dough, we can add the other ingredients. It's a good idea to make tests of this with your clay selections as early as possible, put out a couple hockey pucks or adobes and see what it does. With my clay, the base mix can crack a little (best if it doesn't) but it won't just crumble. My dried product looks like slightly cracked (clay rich) but very hard, warm-grayish hockey pucks.

I should point out that wood ash has lye in it, which is caustic. I've been told that the hardwoods have more lye than the soft but either way, wear gloves and watch your eyes.

To make hard, resilient, (but less insulating) feed box mix; take the base mix and add sand and chopped fiber. You will most likely need to add water to work these into the mix, clay slip can be used instead depending on the stickiness (and/or expansiveness) of your clay. More of the fiber will make it more insulating, less knock resistant; more sand the opposite. (Always, there are exceptions to rules)
Using my soils, (by volume) one part base mix with one sand, from around half to as much as one and a half fiber, depending. Alternately, we could go with one part base, two parts sand, half or less fiber.
Test!

To make high heat insulation mix (that's fragile), I have most often just used perlite/slip. Ash can be added to the mix, when you do, it's easier to mix the dry together first before you add the slip. Wear a good mask when you work with this stuff, you don't want to breathe the dust; when everything is all wet from slip you can take it off (the mask).
The slip (usually) should be wetter than what was used for base mix, add water and mix well. You should pull a thinner glove and it should still look distinctly glove-like, you don't want it to run clean(ish) off and expose skin; the difference between "slip" and dirty water.
Pour the dry out on a tarp (sometimes in a wheelbarrow), perlite and other dry (ash), then sprinkle slip over and gently fold them together; try not to squish too much of the perlite (it's fragile) when you stir it. You can pick up the corners of the tarp and roll the mix around, this works but not as well as turning it and mixing by hand.
You want just enough clay slip to thinly muddy everything and hold together the mix, no more. Pack a ball of it in your hands, it should form relatively easily into a little glob and stay together. When you squeeze this ball between your fingers, it will pop apart. If it smushes without popping, it's generally wetter than I would pack a heat riser with.
The mix can be made deliberately wet (with slip) for a more sculptural, less insulative material. Fiber can be added, alternately you could replace the perlite entirely with organic materials. Wood-chips, forest duff, straw, manures, etc. can be used to make a fairly insulating material that isn't very strong or long lasting but is absolutely free.

For the plaster/slickum material, take the base mix, add water (or slip depending on the clay) and (often) fiber for workability. You can "add up" to whatever property is needed, sand/fiber for more sculptural mixes or wet down for thinner wash layers. Washing can fill pores and lock closed the surface (inside of perlite/clay heat riser), make 'em thicker or thinner for the need. Often, I make a creamy mix like toothpaste and smooth it on thin with a trowel or sponge to seal cracks. I plaster the inside of perlite/clay heat risers with it and I think that a layer of this can help to hold together sawdust/clay parts that would otherwise disintegrate over time.
Base mix is the mortar that I use with fired brick and I use as little of it as possible, then I plaster the whole thing, over all of the brick seams, etc. with a thin coat of watered base.

For casting, none of these mixes are going to be "pourable". Making solid parts is going to be about packing, not pouring.. This might complicate the process of using some molds (batch box) but at the same time it will facilitate a lot more free hand sculpting, which makes it possible to make shapes that would NEVER come out of a form in one piece. More than that, several material types can be combined in one go and dried together. For instance, build up a layer of hard mix with insulation over it followed by a cap of hard mix. The combinations are endless so you can let your imagination and your intuition go a little.

[yannig]

Hello,
I take this thread out of ...mud of time, because i'm realy interested in going toward lower technologies and complexity.
Is this firebox still existing ?
and if no, how long did il last ?
and did someone push the experiment further ?

In a couple of weeks, the french stove-builders yearly meeting takes place, talking about very serious questions and playing with bricks and fire, and baking pizzas.
Among the 5 prepared building proposals, i'll propose a pizza oven based on a batch-rocket firebox.
 i'm very interested in trying a mud-based construction for the firebox, as i would'nt dare to do it in a home presently.

I have questions about the ideal mud-mix, which would resist the high temperature for a while, and wouldn't crack too much by drying.

Available material are : the local red clay, as much as we want.
I have some bags of refractory white clay (maybe 100kg available)
I have some ashes, but not much. what would be ideal for a roughly 200kg mix ?
I have sand, and could have gross chamotte, if needed, but it's part of the challenge to make it as simple and cheap as possible.

Thanks already,
yannig,