Jesse's Modular RMH Experiment

The beginnings of what could be a lengthy thread. Here's the general concept as it now stands:

This thing's going in my basement, despite Ernie's specific advice at the pebble style workshop. It's my best option right now. Since it's gonna be surrounded by lots of concrete (floors and walls), I had this idea that maybe the core part could be in a concretesque shell. As the core will mostly consist of a bunch of molded refractory it won't be too durable. A hard shell could help out in this regard and I can form in some voids to be used as hand holds. I've had this affinity for fooling around with fabric formed concrete for a while, so it's an excuse to do some of that. One of those "you know what'd be cool?" moments for me. Here's an example of a piece of furniture made with fabric formed concrete:

Here's attempt #1 (it failed). I decided to go with bubble wrap for formwork. It's possibly the best texture of all time and if one of these ever needs to be shipped, the formwork could be part of the packing. Problem is, it's too stretchy at this scale and blew out.

more process pics

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what might've been...

Here's what the formed out negative space for my core looks like upside down. Kind of an upside down inside out mocked up look at the guts:

I like it! Very cool idea!

Jesse Biggs : Fantastic!! You have taught yourself an amazing amount of stuff, I really have very little to add except the way the manifold should shape up !

Think of a short length of reducer pipe from say 10 to 8 for an 8''system and 8 to 6 for a 6'' inch system that center section with the cone shape is more the
way that you want to incorporate into your system some thing long enough to allow you to build in sweeping curves to carry you from a Cross Sectional Area
of 3Xs any other Cross Sectional Area at the start of your manifold past a generous ash pit and meeting the horizontal piping NOT abruptly like your 1st
iteration seems to show, but more gently with a mouth like the bell on a trumpet !

As a fellow alumni of one of Ernie And Erica Wisners workshops I am sure you quickly got what I was trying to say, I just wanted to make sure that you didn't
miss that slight improvement and have to retool more latter ! More Pictures ! For the Good of the Craft ! Big AL !

Big Al,
My plan was to have this first piece (a 10" to 8" reducer) connected directly to the manifold and an 8" T, for a cleanout, connected directly to that. Are you saying there should be a bit of a length of 10" before I reduce down?

Looking at the photo, what appears to be a "cone" is actually a 10" void formed in for the reducer piece. It's a plain old 10" cylinder.

Maybe a little better angle:

Jessie Biggs : In the south there is an arachnid called the ant lion it digs a cone shaped hole and when an unsuspecting ant fails in rather than fight the ant
the ant lion just waits for the ant to wear itself out trying to climb out of the hole ! In the case of the manifold we want a tapered or cone shape rather than
what you have, gases turning to flow out through the manifold creates turbulence where we don't want any ! This is why rather that having a chunk of pipe
stuck in there as part of the mold you should be creating a wide mouthed receiver that tapers with gentle curves gradually downsizing to the Cross Sectional
Area of the horizontal piping ! Think of looking down into the bell of a trumpet, and not the hole in the sounding board on a guitar !

Thn again you probably got it the First time and are enjoying pulling my leg ! BIG AL !

Not pulling your leg at all Al. I think I get what you're saying. At the workshop, I think E & E stacked one barrel on top of another that was cut way down to just a stump. It had the feed tube and burn tunnel kinda stuck in from one side, the riser extended up into the top barrel, and the manifold, if I remember it right, was simply some 8" coming out the other side of the bottom "stump". Could be wrong but that's how I remember it.

This form is upside down so after it's molded it should resemble something like a tilted fat horseshoe + wedge shape with a 10" hole at the bottom reducing down to 8" and a clean out. I get the gentle non-turbulence thing and will probably mold this "as is" and possibly attempt to make it gentler and smoother after that. Hopefully pics will be coming in the next few days. I'm posting this stuff pretty much in real time.

Big Jesse : Da nadda ! no big thing, like i said now is the time to catch it, ernie already knows what he could get away with, having made dozens and dozens
just like that one before ! You are carving new territory and now is the time to be generous, I am reasonably sure that he or Erica will be checking in soon
so you can get a second opinion then ! This is new stuff, this is great stuff ! Keep it coming, More pictures ! BIG AL !

We've done smooth tapered manifolds (from cob and other materials), rough brick ones, and cylinders or boxes with relatively smooth walls. Never noticed any big differences in performance, except where the shape was too small (narrow slots) or where fly ash clogged it down too small.
The fly ash that builds up in there makes the precise details of the surface and shape kind of a moot point. Ash will settle around the walls, and if allowed, will accumulate everywhere there isn't sufficient flow to blow it away. Which is most of the manifold. There may be some advantages to certain shapes, but they pale beside the basic rules: no cross-sectional flow restrictions, including room for ash; and accessible maintenance cleanout where you can remove the ash annually.
Because ash buildup is the main issue, I even like to see the pipe enter the chamber somewhat above the floor, to make a 'settling pit' (like a settling pond) and reduce the amount of ash that can build up to block the pipe. This does mean a sudden transition from big space to smaller pipe; I've never worried about it, and our performance parameters work around similar variations in the design.

We do find that smooth, tough walls are a big advantage when it comes to cleaning out that fly ash without inadvertently 'cleaning' away part of the rough or irregular walls. (especially with cob). Leaving the cob rough is just asking for some enterprising chimney sweep to vacuum the whole thing up one nubble at a time. Sometimes I embed tile scraps or other materials in a cob manifold, just to let future cleaners know when to stop digging.

-Erica

Erica : Point taken, sometimes I have a tendency to nap in the afternoon, especially with a full belly and the sound of rain on a tin roof, I must have missed that
part. SO- smooth enough to not trap fly ash, or give some ham handed hose jockey an excuse to get in there and grind away at things better left alone ! And
make the Transition zone, and the ash pit big enough, got it !

Thats the fun of Adult Education, because we have to be convinced that we 'need to know' that next piece of information you are trying to share, you can't always
be sure that some important message was not filtered by the listeners preconceived ideas - and changed!

You and Ernie tried so very hard to pound it in there,but I guess part of that bucket load slopped over the top, or leaked out through the extra hole in my head!
of the many people you and Ernie have touched, few people were helped more, and I get to prove it every day in these Forum Threads ! Big AL!

almost ready for mud:

then when it's dry, flip it over and try to salvage as much of the mold as possible... that's the plan anyway

What kind of mud will you use?

John, I'm going simple with perlite, fireclay, and some chopped up fiberglass rope gasket for tensile strength. Due to podcast 267, I'm retooling the overall design a bit. More to come shortly.

Well I hope it works, because it's beautiful. I'm also curious about what in the podcast has changed your mind.

Two things really. The black stove pipe is something I hadn't realized, so that needs to happen, and I now want to make the run about 10 feet shorter, possibly with one less elbow. Oh, and one more, the exhaust will be situated closer to the bell for the secondary pumping action.

... almost forgot, me too and thanks!

Ok, I thought you meant you were going to change the design of your core.

Here's the mud in all its precast glory. After some delay it's going down today.

Hey Jesse,

This is awesome work! I can't wait to see how that works! The form looks beautiful, I love the aestetic. How much do you think it will weigh when dried? As well, do you plan on forming it on site? Or, are you planning on moving it to your final site?

Thanks Tyler. I don't know how the weight is going to shake out. Working with insulating type materials is throwing some curves at me. I've got four 50lb. bags of fire clay and I'm mixing that 50/50 with perlite which weighs next to nothing. Hopefully I won't go over 200 lbs. as the idea is that this could be moved out of my basement at some future point. I'm forming it in my basement which is also its first resting place (fingers crossed it works out!) The plan is to build the whole thing in bite sized "modular" chunks that could be moved with a few extra hands and w/ out too much difficulty.

Jesse Biggs wrote:Thanks Tyler. I don't know how the weight is going to shake out. Working with insulating type materials is throwing some curves at me. I've got four 50lb. bags of fire clay and I'm mixing that 50/50 with perlite which weighs next to nothing. Hopefully I won't go over 200 lbs. as the idea is that this could be moved out of my basement at some future point. I'm forming it in my basement which is also its first resting place (fingers crossed it works out!) The plan is to build the whole thing in bite sized "modular" chunks that could be moved with a few extra hands and w/ out too much difficulty.

well, please keep posting the progress. I am looking forward to see how it works.

Jesse,

I gathered from another thread that you've had some setbacks with this design and maybe are rethinking it. If that's true, could you discuss those setbacks here? I really like this design and am planning on pretty much copying it, but I'd like to know if and why you think it has problems.

Yeah, been meaning to do that. First off, due to podcasts 267 & 268 I changed the overall layout. Fewer elbows, shorter overall run, and vertical exhaust closer to the barrel.

I'm really just talking about the core. Have you cast it in that mold yet, or modified the mold?

Mostly, the core has been the sticking point. Having spent far too much time building large cardboard forms, I've finally come to grips with the fact that it's not going to work out. The clay and perlite want to be formed in a more additive/sculptural way. I ended up ripping the outer shell of the cardboard form off and packing mud around the inner cardboard bits. The cardboard doesn't hold up well to the abuse and the process is just too slow! In the back of my head, I want to solve the problem of making this a quick and repeatable process with less wasted time and material. Here's a pic of the core as it currently sits... It will eventually be broken down and recycled into slip (fingers crossed). I would bite the bullet and finish it "as-is" just to get the rest of the experiment under way, but that's just not how I roll I guess. MUST SOLVE CORE ISSUES FIRST.

The latest idea is to "slip cast" the core. There have been a few failed plaster cast attempts already. I thought I'd taken some pics but can't seem to find them. In the works is a 1/2 scale core using the new technique. As things now stand, the core will be cast in 4 easily assembled pieces.

Thanks for the pics and update. It's a shame the clay/perlite on cardboard isn't working. I still want to use the cast refractory formula Erica used, but in my preparation I realized I'd need around 5 cubic feet and that's with no manifold! That's just so much, it's gotta be too heavy. Your mold not only looks better, but I think it's less volume to cast.

I like the way your new design fits together though. I hope your slip-casting plans pan out better!

Hi Jesse, John

Wow I really like the slip cast idea! It's beautiful! What ratio of mix are you using? (Edit: never mind. I see it the there in your post of Dec 17, 2013, 10:44PM)

On a YouTube video - I cannot remember which - I saw a guy mixing vermiculite and refractory at a 4:1 ratio for his rocket stove in a 5-gallon plastic bucket. Is his 4:1 ratio workable in a 20- or 30-gallon system?

Btw I found vermiculite at Home Depot for $20 for a 2 cu.ft. bag.

I already had plans to cast the core (riser?) of my first stove... See drawings attached here, which I recently posted in my own thread here, but I hadn't considered pre-casting the entire form (excepting the barrel, of course).

Actually now that I think of it I wonder if a concrete pre-cast fabricator could make these things with a given receive of castable refractory and vermiculite. There's a huge market!

See my drawings attached here. I'm curious, what are you using to make the form molds? Are you able to share other drawings or tips here?

Kevin Prata wrote:On a YouTube video - I cannot remember which - I saw a guy mixing vermiculite and refractory at a 4:1 ratio for his rocket stove in a 5-gallon plastic bucket. Is his 4:1 ratio workable in a 20- or 30-gallon system?

...

Actually now that I think of it I wonder if a concrete pre-cast fabricator could make these things with a given receive of castable refractory and vermiculite. There's a huge market!

See my drawings attached here. I'm curious, what are you using to make the form molds? Are you able to share other drawings or tips here?

Kevin, wow! 4 vermiculite to 1 part refractory? That would lower the cost substantially. What flavor of refractory are we talking?

Looking at your drawings, I'm curious about the exhaust coming out the back bottom of the barrel. How is that attached and is it going into a cob mass from there?

I'm using more cardboard molds to develop plaster molds for slip casting clay and perlite bits that can be assembled. It's all new to me and experimental so I'm just going for it and seeing how it works out. I'll keep posting pictures and drawings as I can.

Hi Jesse

Thank you for comment.

The flue attachment will probably be a flange bolted onto the barrel, or maybe I'll just glue it on with some JB Weld.

That guy was using a 4:1 ratio vermiculite + refractory, but he did not say what brand or what sort of refractory.

I notice that Broaudio at YouTube is using Heat Stop II, and Paul Wheaton prefers vermiculite over perlite (but Broaudio prefers perlite for a small budget, I suppose).

I haven't started yet, but I'm pretty darn close. I am hemmed in here by crummy weather, and, besides, I'm still gathering the last few components before I start -- principally, the refractory and the wool blanket. On that note, another poster here on permies.com suggests using a "extreme high heat welding blanket" that can stand up to 3000d F; yet, it is expensive. I found a superwool / inswool blanket available at $3.50/ft. I'll cast the inner 1" wall riser from the refractory mix, wrap it in 1" superwool blanket, and setup another 1" cast layer on the outside of the blanket. That should keep any asbestos, ceramic or glass fibers from peeling off the blanket.

Kevin, I'm pretty sure Paul prefers perlite. The core currently in his office is made of 3 materials... clay (from the lab), perlite, and wool (from a sheep), and he says it's holding up nicely. I think perlite is more insulative than vermiculite but I'm just going with what I "think I heard once". At any rate, it's what Paul, Ernie and Erica use so I'm moving forward with confidence.

I've played with a few different materials and even bought some expensive castable refractory (mizzou). It's still sitting in my garage waiting for the right application. There are lots of really cool and expensive things to play with in this space.

If the ingredient list gets paired down to just clay and perlite, your average joe (me) can afford to tinker. I really like the idea of coming up with reusable forms that can cast cheap and accessible materials. Fingers crossed it works out. It'd be the first thing that did thus far .

Hi Jesse.... Hmm where did I see that preference for vermiculite over perlite? I cannot remember now. Maybe it was from Donkey or Eric at Proboards.com.