Jesse's Modular RMH Experiment

John, that may be exactly what I need. Any idea how much heat the cloth can handle?

John Adamz wrote:Will there be some kind of finish coating on top of the pebbles?

My wife and I will be working on cushions of some sort. Already the kids feel like they need to treat the benches like sand boxes.

Also, I just remembered I got some fiberglass rope gasket a while back. I might try making it into a few rope rings and working them into the riser somehow.

Jesse Biggs wrote:John, that may be exactly what I need. Any idea how much heat the cloth can handle?

A bit of quick inquiry gives me results of ~1000deg F continuous direct contact. As a note on heat tolerance when I used regular fiberglass house insulation to insulate between the half thickness firebrick riser and the sheet metal duct surrounding it, the bottom ~8" or so next to the riser melted I've since redone that and used vermiculite with no problems since.

I still think just some plain chicken wire would work to hold riser cob in place. I also think that cob mix should be heavy on some perlite or vermiculite to increase the insulative value.

Jesse Biggs wrote:By way of an update...

So between pics 490 and 502, did you wait for the cob to set up some before hand-sculpting the manifold?
Or was it stiff enough when poured to do it?
Is there an internal mold for the manifold transition to the bench?
I was wondering why there were two sections of riser. Is this where the failure is?
Please, more details on the riser issue!

I'm following your progress, and I like the way you're going. It makes me want to do my own. Just need a little fireclay...

Cam Mitchell wrote:
So between pics 490 and 502, did you wait for the cob to set up some before hand-sculpting the manifold?
Or was it stiff enough when poured to do it?
Is there an internal mold for the manifold transition to the bench?
I was wondering why there were two sections of riser. Is this where the failure is?
Please, more details on the riser issue!

It seems like it dried overnight, but could have been sculpted right away. I ended up not really "pouring" so much as making baseball sized globs and mashing them together one at a time.

There was was no internal mold. I used a tape measure, large compass, filet knife, dry wall rasp, and my hands.

The two sections thing came about because I was trying to do a kind of mold and knew I could reach all the way to the bottom of a 16" section as opposed to a full 32". Also, 2 short sections were easier to move and place.

I think the failure had more to do with putting fire to things while they were still VERY wet (got excited, and impatient), as well as not providing any kind of tensile strength reinforcing. I'll be posting pics of the damage probably when I can show what I've done to try and fix things.

While talking to Paul, he seemed to think that I'll need to do something totally different with the riser. I know they're using some pretty pricy and fancy risers at the lab that work really well. I want to continue to try and come up with something cheaper though it will probably lead to more failures and frustration and I'm ok with that.

Cam Mitchell wrote:

Jesse Biggs wrote:By way of an update...

So between pics 490 and 502, did you wait for the cob to set up some before hand-sculpting the manifold?
Or was it stiff enough when poured to do it?
Is there an internal mold for the manifold transition to the bench?
I was wondering why there were two sections of riser. Is this where the failure is?
Please, more details on the riser issue!

I'm following your progress, and I like the way you're going. It makes me want to do my own. Just need a little fireclay...

I mentioned fiberglass before talking about the molds. What do you think about woven roving instead of the mat. Say a 24 oz.Its a lot heavier and I think you could get the cement actually worked into the weave

Dave - I like the idea of using fiberglass, and if I understand right, roving is different in that it is woven? A material that offers tensile strength and can take the heat seems like a logical fit. fiberglass is something I haven't played with much so it'll take me a bit to figure out terminology, sources, and other details.

Jesse-
I'm not sure how cost effective using fiberglass is but here's an ebay item fairly cheap. fiberglass roving 30"x10yds 24oz
You can search for different size/cheaper options.
I was unfamiliar with the different types of fiberglass material other than what I've used in auto body and boat repair until now.
It clearly won't stand the internal temps of a riser, so I can see possibly using a thin layer of a more refractory cob mix on the riser pipe then applying the fiberglass then more cob to desired diameter then just wrap with chicken wire and smooth over.
I can't recall what type of other material I've read being used in a similar way, but it might be cheaper.

Hey, Jesse. This project looks like a lot of fun and very useful. I saw another company making RMH shippable cores and saw they were using the multiple-piece approach, as well. I like the look of your cores better, though!

http://www.dragonheaters.com/rocket-mass-heater-shippable-core/

Jesse, you could just stack firebrick to make a mediocre riser. Firebrick wrapped in a layer of rock wool makes a pretty decent heat riser.

Paul, I figure it's not the best option, but I really don't want to buy more stuff if I can avoid it. I've got lot's more clay and perlite, some rope gasket, and lots of chicken wire. This might get me through the rest of the winter. In the meantime, we'll be working on better stuff!

Jesse,

I just posted my idea for cast-able riser bricks. I won't be in the position to test out this idea anytime soon, but if you are experimenting with possibilities, I'd love to see how this might work in the real world.

Here's what the riser looked like when I pulled the barrel off earlier this week... and to think we were having trouble getting it to draw .

Next up, More cobbish over chicken wire with some time to dry before firing.

Jesse Biggs : While I was successful in using two pieces of large diameter stove pipe as the Bread in a Perlite/Clay-slip sandwich, others have reported cracking
that they blamed on the Expansion of the inner Steel piping, i only have anecdotal evidence of them being more successful when they used a cardboard sona- tube!

Just sharing for what its worth ! Big AL !

Thanks Allen, I don't feel incredibly confident in what I've done here. In a couple days I'll be able to report back. If I need to buy more supplies to make it work, it'll probably be bricks and rock wool like Paul suggested.

Jesse Biggs wrote:Thanks Allen, I don't feel incredibly confident in what I've done here. In a couple days I'll be able to report back. If I need to buy more supplies to make it work, it'll probably be bricks and rock wool like Paul suggested.

Jesse, you have a lighter and easier option at hand.

http://www.superiorclay.com/flue-liners.php

http://www.sandkuhl.com/Flue%20Liners.html

They do crack once, at least the Landini ones i have from Italy. But tightly packed into a layer of vermiculite, perlite or rockwool and they hold perfectly afterwards. In my latest builds, i've used round or square. Surounded by vermiculite, and a steel tube to hold it all together. No clay whatsoever.

another thought on a riser. More of a question. I was out rummaging around at a place and found a piece of 6in well casing. Its pretty thick,probably 1/4. Would something like that last.? it could have hardware cloth attached about a 1/2 inch stand off and have the fireclay packed in it

Dave, if I'm understanding you, sounds like there are a couple issues with that. First, all metal will eventually burn out. The temps inside one of these bad boys are just too hot for metal. Second, you need the riser to be insulative. You need something like perlite or rock wool involved in the riser to help the system draw and work correctly.

Some of the reasons Paul doesn't love using the galvanized tubes: first all the galvanizing burns off and sends green smoke out the end. Next the tubes turn into powder over time. You are left hoping that whatever other materials you used have been vitrified or hardened to the point that they can stand alone.

At any rate, I don't think 1/2" of straight clay will do the trick for you.

I understand I guess i thought that since it was so thick it might with stand. And my idea was to wrap it in hardware cloth so that the fire clay could be packed around it. Kinda like mat in concrete. I'm just throwing things out there as I am learning and living vicariously through you. I'm in the middle of a Tinyhouse build and sand filters right now And trying to survive the winter

Dave, does your tiny house have a thread? I'd like to see what you're up to. Sand filters sound cool.

No I dont have a thread. i have pics on facebook. Its about half done but I am a cabinet maker by trade so i am doing everything including windows,cabinets an doors. But the weather aint helping But I am just an old guy on a journey. Been foolin with this stuff since before John Shuttleworth. As far as sand filters they are pretty simple. i use to 5 gal buckets I got at Lowes. They are made from the same plastic Milk jugs are made from. I stumbled on these dang RMH a couple years back and they have been under my skin. I knda want to see how small I can make one. Untill i move into a bigger place anyhow.

Keep up the good work !

In some areas (I think mainly on the east coast), vermiculite is much easier to obtain than perlite.
However, there's a structural difference that has some effect on castings.
Nice to see progress on various casting options!

Regarding perlite vs vermiculite:

Perlite is little bobbles of 'rock foam' - basically rock popcorn, made from pressure-popped gaseous obsidian or volcanic glass with gas inclusions. This means perlite has very small pores, and retains its insulation value in a lot of different uses and combinations. Also, the "rocks" are easily crushed with sufficient force, but it takes a fair amount of pressure. Stomping on a footprint-sized bunch of them will crack or crush a few of the bigger ones, but the smaller ones remain relatively unchanged.
Very wet solutions penetrate easily, but it's also pretty easy to coat the outside with clay slip or cement and still have air spaces trapped inside each chunk. The castings I've seen with perlite show good bonding between the cement and the perlite; and when broken, you can see lots of white dots where the perlite did not absorb the goop. The insulative performance also seems good.

Vermiculite is little flakes, like mica. I don't know whether it's popped or milled, but the samples I've seen are easily disintegrated by rubbing between the fingers. The usual process for mixing cement or clay can break down these chunks pretty easily, and the goop may also penetrate between layers (not sure on that one). Vermiculite may be a comparable insulation material when dry, but in wet / pourable applications it seems to lose a lot more of its insulation value than perlite. It's also poorly bonded to itself, so larger vermiculite chunks could become a weak point in thin-walled castings. We have not tried casting with vermiculite due to prejudice.

We prefer perlite over vermiculite for our own experiments. When building brick-type heater cores, we suggest using 2" of perlite or 4" of vermiculite. (Or 1" to 2" of fiber-type refractory insulation: ceramic fiber, rock wool.)

If you only have access to vermiculite, it's worth doing a little experimenting to see how much you need to change the process (thicker walls, e.g) to retain similar insulation and strength properties.

As a final note, both materials (and every known type of insulation) can give off very fine particles of dust. These are not good to breathe.
We recommend well-ventilated spaces, dust masks, and/or pre-wetting the material before dumping it out of the bag to control dust.

-Erica W

Erica Wisner wrote:In some areas (I think mainly on the east coast), vermiculite is much easier to obtain than perlite.
However, there's a structural difference that has some effect on castings.
Nice to see progress on various casting options!

Regarding perlite vs vermiculite:

Perlite is little bobbles of 'rock foam' - basically rock popcorn, made from pressure-popped gaseous obsidian or volcanic glass with gas inclusions. This means perlite has very small pores, and retains its insulation value in a lot of different uses and combinations. Also, the "rocks" are easily crushed with sufficient force, but it takes a fair amount of pressure. Stomping on a footprint-sized bunch of them will crack or crush a few of the bigger ones, but the smaller ones remain relatively unchanged.
Very wet solutions penetrate easily, but it's also pretty easy to coat the outside with clay slip or cement and still have air spaces trapped inside each chunk. The castings I've seen with perlite show good bonding between the cement and the perlite; and when broken, you can see lots of white dots where the perlite did not absorb the goop. The insulative performance also seems good.

Vermiculite is little flakes, like mica. I don't know whether it's popped or milled, but the samples I've seen are easily disintegrated by rubbing between the fingers. The usual process for mixing cement or clay can break down these chunks pretty easily, and the goop may also penetrate between layers (not sure on that one). Vermiculite may be a comparable insulation material when dry, but in wet / pourable applications it seems to lose a lot more of its insulation value than perlite. It's also poorly bonded to itself, so larger vermiculite chunks could become a weak point in thin-walled castings. We have not tried casting with vermiculite due to prejudice.

We prefer perlite over vermiculite for our own experiments. When building brick-type heater cores, we suggest using 2" of perlite or 4" of vermiculite. (Or 1" to 2" of fiber-type refractory insulation: ceramic fiber, rock wool.)

If you only have access to vermiculite, it's worth doing a little experimenting to see how much you need to change the process (thicker walls, e.g) to retain similar insulation and strength properties.

As a final note, both materials (and every known type of insulation) can give off very fine particles of dust. These are not good to breathe.
We recommend well-ventilated spaces, dust masks, and/or pre-wetting the material before dumping it out of the bag to control dust.

-Erica W

thats great experienced info Erica

im curious if this beautiful RMH is still holding up after 2 yrs - Jesse?.
btw- the kids hand prints are a nice personal touch!

I know it's 2 yrs old but I was looking at the "best ever" threads and I found this, I'm curious about the longevity and recipes of these cast cores as I'm about to cast one myself, which will be my 2nd stove designed and fabricated by myself. I understand by jesses recent popular wofati posts that he is still here at permies...? Besides after 2 years should show of any longevity and/or premature problems. I'm just trying to see how these cast cores turned out from experienced people whom have done it.

Jesse Grimes is the ant currently at Wheaton Labs.

Glenn Herbert wrote:Jesse Grimes is the ant currently at Wheaton Labs.

i was reffering to Jesse Biggs - the author of this post

Jesse Grimes has been posting a lot about wofatis at Wheaton Labs; Jesse Biggs last posted on July 7, 2015, on his home backyard project: https://permies.com/t/34620/projects/acre#387729