Best RMH Insulator once and for all?

Hi all,

I have access to the following and would like to know which one, or which combination of the below would best serve as insulation for the burn tunnel, the heat riser and to go between the thermal mass and adjacent wall. Trust me when i say the last part is necessary in my case..

- Horticultural Perlite
- Wood Ash
- Sawdust
- (and clay slip to mix with one or more of the above)

Couldn't get any tiles from off the space shuttle to recycle?

Seriously though, the best insulator is going to be the lightest material, from the items on the list, it's the horticultural perlite. You could do an experiment and mix up your clay slip with different materials and let it set up and then test the blocks. Weigh them and then test the thermal conductivity by laying them on a stove burner and measure the temperature on the top of the block. What I think you will find is that weight is inversely proportional to thermal conductivity.

Thanks John for your reply!

The reason why i ask for the three different insulation sites is that on the heat riser i believe the sawdust for example will incinerate, whereas between the bench and the wall, if i run out of perlite by then, the sawdust may work fine as it will be in contact with much less heat (?)

Ill probably do just perlite around the burn tunnel, then perlite and clay slip around the heat riser, then whatever´s left of the perlite and maybe sawdust and ash between wall and bench.

If this sounds like a logical plan, great..but if there´s something i overlooked or if my intuition is off then pleae advise!

P.S. do they sell space tiles at used prices on amazon?? ..j/k..

Karl Meisenbach : I can give you my opinion,someone else may have a slightly different order that they place them in !

Horticultural Perlite is a little bit dusty, because it does not have the uniform particle size that other grades have, it will make a slightly wetter mix with clay slip!

Wood Ash from a Rocket Mass Heater, is just mineral ash, and would make a slightly stiffer mix added into the perlite and might actually correct for the wetter
Horticultural Perlite !

Wood Ash from a regular wood stove, mostly grey and containing minor amounts of small chunks of black charcoal should also make a stiffer insulative mix when
added to the perlite and clay slip !

Sawdust must be dampen'd when mixed with clay slip otherwise the sawdust will suck up all the water before the clay slip and sawdust can bind - after the sawdust
burns up you are left with a very light and fragile Heat Riser best incased between inner and outer metal skins ! Its durability is questionable !

A Heat Riser made from A mix of Perlite and Clay Slip should have just enough Clay Slip to darken all of the Perlite and the two should easily form handball sized
balls that pop apart when squeezed, The resulting Heat Riser should last for years and can be recycled when it starts to fail ! It too should be lightly packed between
inner and outer metal skins. Without an outer metal skin the heat riser must be made up in sections and dried before use, it probably will not be as strong and even
with an wire mesh outside wrap the material removed from the clean out in/at the base of your R.M.H. should be carefully screened for evidence of failure of the Heat
Riser !

For a couple of videos showing construction of Heat Risers, go to Permies' sister site richsoil.com and click on the link to Rocket Mass Heaters there are a bunch of
short Videos. If you have not watched them by now you should ! Good luck - You are getting close to Cob Dancing ! Think like Fire, flow like Gas !

For the good of the Craft ! Be safe, keep warm ! As always, your comments and questions are solicited and are Welcome PYRO - LOGICAL Big AL

Hi Allen,

Are you taking into account that my heat riser is 100% made of refractory bricks and that i plan to insulate around it with perlite w/clay slip encased in a wire mesh? How would the wire mesh hold up in these conditions with an 8" system?

Karl Meisenbach : I did not take into account that you would be using Refractory bricks, I just answered the question as asked, I try hard not to read too much into a
question, or I find myself telling someone to completely rebuild his system for a perceived flaw they are not even having problems with !

My efforts in trying to help Anyone living outside of 'the states' has been very frustrating to me and the people I try to help, I am So very used to the vast stream of
easily found materials available here that it is hard for me to wrap my head around how difficult it can be to 'Do more with nothing'! Again we have a similar problem
here !

I do not know how you are going to pack your Perlite/Clay Slip around your refractory bricks without a stiff walled outside form. Your problem comes two ways, pack
it too tight, with too much Clay slip your insulative over coating will be stiff enough to hold together during your drying phase which should ( I think!) be part of
your outdoor testing phase, done prior to placing the barrel down over your Heat Riser. However too much (?) Clay Slip to Perlite, will not be as insulating as possible.

Your mix of perlite / Clay slip must not slump during this phase because you still need to get your barrel over the top of your Heat Riser and guarantee you minimum
1.5'' air gap !

Too much perlite with too much water content, (I have never used Horticultural perlite before ) will not allow for a stiff enough mix to guarantee your Perlite/Clay Slip
Over-coating will be strong enough to last, possibly even wrapped in a metal shell !

I hope that another member can add to this discussion. Given the trade offs I have just described, any metal shell on the outside of the combined Heat Riser that holds
in the materials and guarantees the gap is the best/first way to go. Second best would be a stiffer, well packed mix of Perlite / Clay Slip wrapped with a very stiff walled
fine meshed wire overwrap. It must allow any material that leaks out through the spaces to be easily cleaned up, as we must be able to guarantee the 1.5'' gap between
the Total outside diameter of the Heat Riser and the inside diameter of the barrel !

For the Good of the Craft ! be safe, keep warm ! As always your comments / questions are solicited and are welcome ! Big Al !

Allen,

Thanks again for taking the time..i think im just going to go ahead and fit the wire mesh around the heat riser, measure the gap, then fill the space between the two with perlite/clay slip. Maybe a bit less clay slip because horticultural perlite is supposed to be more absorbant, or maybe i should use more clay slip for that very reason(?)

Then i plan to dry it on site with my first few "test drives"

We shall see...

Karl M. : No matter what happens all your Perlite/Clay Slip trials will be totally recyclable, your Horticultural Perlite is expected to hold more water than most other Perlite!
Inside a flower pot the ability to hold more water is a plus, for making a good stiff Heat Riser, not so much.

Once again you find that we Norte` Americano`s can run our mouths and tell you what you ought to have and what you ought to do, and then you turn around, re-afirm
once again, that you are the one doing '' More with Less !'', and get the job done ! My hat is off to you, show us how it should be done !

Please keep good notes,take pictures and please, please, please share your results here at our Rocket Stoves Forum ! We need the addition of new knowledge to shake
us up and get us out of ours ' we've always done it that way deep, deep, rut ! Think like Fire, flow like a Gas!

For the Good of the Craft ! Be safe, keep warm ! As always your comments and questions are Solicited and Welcome ! PYRO - LOGICally Big AL !

Karl, have you thought about rockwool?

i have thought about rockwool but i thought that encasing the brick heat riser in the stuff would cause it to emit noxious gases..am i wrong?

Oh and Allen..im actually an American living in Uruguay..im learning from you guys, Iantos´rocket stove book, and youtube. I just want to get it right the first time and have it last for a very, very long time so im nit-picking at the details..

Pictures are already in effect..if its anything like i imagine in my mind then it should be pretty cool..

Karl Meisenbach : Rock wool is a spun glass,and is inorganic, It is also like fiberglass ,only without any of the resin, or any other organic, binder or sealer at all. If
heated high enough the Rock wool will fuse from the outside inwards, never fusing enough to make a thin shell of fused Glass !

I thought that, I understood that, -you had not been able to find Rock Wool where you are, and Were considering other choices ! Because I often get In trouble
when I assume things, I try to answer the questions asked, but once again I allowed my Expectations to cause me to assume ! For that I am sorry, please excuse
my mistake !
For the Good of the Craft ! Big AL !

Karl Meisenbach wrote:i have thought about rockwool but i thought that encasing the brick heat riser in the stuff would cause it to emit noxious gases..am i wrong?

http://en.wikipedia.org/wiki/Mineral_wool

Thank you Satamax!