Any substitute for perlite/vermiculite for rocket stoves?

Hi, we live in the middle of the African bush and I would really like to build a rocket stove heated seat on our verandah for the cold winter nights we are entering now. Perlite and vermiculite are not things I have been able to find. Are there any alternatives?

Thanks

Hi Zim; Welcome to permies: You can build your rmh without using perlite/vermiculite. The main use of perlite is to insulate your firebox, unless you were wanting to build a cast core or a cast heat riser. Using bricks (hopefully firebricks) you build your core & riser then cover the core with cob (clay,sand) mixed with straw. This will help insulate the core causing the heat to travel up your riser and then down thru your mass. Your riser should be wrapped in a insulator also. Using metal tubing is the normal way of moving the heat thru your mass, but the same thing can be accomplished using a brick tunnel. The beauty of a rmh is it can be built with whatever materials you have on hand. Also being built out of "mud" they can come apart easily and be reconstituted as new cob by crushing up and adding water. Build your rmh with what is cheaply available and enjoy sitting on a nice warm bench in the eavning!

dry ash

Yes yes and more yes. Here is a resource to a rocket specific forum, which is the largest i know of. If you provide some more details, it will help members answer your needs more accurately and efficiently.

http://donkey32.proboards.com/

Or tufa, a very light volcanic rock. In fact, anything that's heat resistant and has low mass.

I have heard of people mixing in saw dust, which ends up getting burnt out by the high heat, but the idea is it holds it's place long enough for the clay to set up around it before the saw dust burns up, leaving behind a tiny spot of air space. And air is a really good insulator.

If heat accumulation is a concern, I would suggest adding air channels to allow cool air to enter at the bottom and flow up, as it heats. See some of the Wisner's builds for examples. I did something like this last winter and it worked very well for me. I was very pleased with the results.

And obviously, for the insulated cob surrounding the insulation used around the firebox, straw is a very common, popular choice that has met with great success.

Thank you for all the responses I am going through Ianto Evans book at the moment. I like that RMH can be built using many different materials. I'm interested in the wood ash suggestion, if I mixed this with clay instead of the perlite would that be good insulation around the heat riser? I am currently building my second earth oven and have built an adobe home so I have experience using earthen materials(and love it!)

I think Shilo was referring to dry ash in bulk filling cavities, rather than mixed into clay. I have heard that ash can have beneficial properties as part of a mixture, but I don't think insulation is one of them... I could be wrong though.

Sawdust or straw in high proportion mixed with clay will certainly give insulation as the organic matter burns out and leaves minute air spaces. This may be the cheapest and most readily available form for you. Such a material will be weaker than structural cob, but will stand up fine when enclosed in stronger material.

If brick is not easily available, you can build the combustion zone entirely of cob, using some sort of combustible inner form to give the flame path the correct shape. Test your clay first in some very high heat device, or in a test build outside, to be sure it can stand up to the heat generated. The inside surfaces will actually become pottery.

ash is insulator only if it dry and loose.
not inside a cob mix.

Zim Lion : I have from time to time heard stories of people in the bush who have used chiseled into Termite Mounds to make Rocket Stoves
and have a '' Boil-up ''

You may or may not have an opportunity to test this possibly apocryphal tale, I have heard that the Termite mounds were nearly as hard as Concrete
but relatively light .

Thyere are acceptable grades od Per+lite called Horticultural Perlite and most greenhouse owners will have at least heard of it ! God luck ! Big AL

Expanded clay works and is very cheap. Building suppliers and garden centres sell it.

Sand?
I thought about this, as well, and watching one video it was mentioned that someone used sand as part of the mass but that this was inappropriate because sand insulates... So there ya go, i thought.
Would it be the best insulator? Probably not. But it's everywhere and free. And often 'the best' can be substituted by simply applying more of what might seem an inferior product.

Socrates Raramuri wrote:Sand?
I thought about this, as well, and watching one video it was mentioned that someone used sand as part of the mass but that this was inappropriate because sand insulates... So there ya go, i thought.
Would it be the best insulator? Probably not. But it's everywhere and free. And often 'the best' can be substituted by simply applying more of what might seem an inferior product.

Technically, it is the multitude of tiny air gaps between the sand that insulate

Sand mixed with clay, for example, is not at all insulative, but rather adds structural support to the clay, helps it not to crack so much, etc.

But if you fill a bench with sand, yes, that is going to insulate to a reasonable degree because of all the air pockets that are trapped between the particles of sand, and *air* is a very good insulator.

So I say go for it! Just use more of it.