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Pack McKibben
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I want to use rock wool or mineral wool insulation in my heat riser, around the J-tube and next to the wall that my RMH is going to built along. BUT, living in a small town, I haven't been able to find any store that sells either. I've called Home Depot, Tractor Supply, the local Hardware stores,
Fireplace & Hearth stores, Farm Supply's, and even Applegate. Where on earth does everyone find their rock wool? Before you answer "use perlite".
That is not to be found 'round these parts either.....
 
brian hall
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dont know how you feel about ordering offline but that stuff is super light weight. shipping would be real low...
 
brian hall
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home depot sells rockwool..... oh wait that is until you click on the link in their website and get no results...wtf? lol
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brian hall
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take a look @ this

http://www.mcgillswarehouse.com/hf11-ceramic-fiber-blanket-1in-8lb-ft3-or-128kgm3-h1cf2cf3c
 
Cindy Mathieu
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Lowe's sell Roxul in various thicknesses and widths. You can order it and have it delivered to your nearest store...no shipping charges.
 
Cindy Mathieu
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On the other hand, it the spots you are intending to use it, you should go with ceramic blanket rather than rock wool. Ceramic blanket can handle higher temperatures.
 
Pack McKibben
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I've been calling everywhere, all day long and can find it. At Lowes and/or Home Depot, they both have a $20 dollar shipping handling charge for a $26 dollar item (approx 48 sq.ft).....I don't like that. If I could pick it off the shelf, IE stocked, I wouldn't have to pay a shipping charge. In my quest to reuse, recycle, repurpose, etc....I also try to get it at a good price. Of course, I may have to pay a premium for this. But, I'll most likely use a vermiculite clay/slip mix instead....if I have too. This was going to be used next to the straw/clay slip infilled wall and I wanted to use a good hi-heat insulation.
If I don't use rockwool....what's the next choice? I can get vermiculite 'round these parts....no masonry type perlite is available.
 
Pack McKibben
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Cindy: I did talk to a guy today, at one of the many places I called, and he said I'd have to place a $400 order (minimum) for his ceramic blanket insulation....
this, at a fireplace/stove/patio type store.
 
Cindy Mathieu
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You could look for vermiculite board, but its delicate and expensive. Someone on a different thread mentioned that Amazon sells the ceramic fiber blanket.
 
Pack McKibben
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Brian: that's the kind of day I'm having. I looked at Home Depot too. Both rock wool and mineral wool are listed in the insulation category. But when you click on it, it says zero matches.
 
Pack McKibben
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The more I call and check on rock wool, the better it's price sounds.
So far the best deal? McMaster Carr......2.8 cu ft; 30 lbs of fill (loose) rock wool $27 bucks with $20 shipping...item 9332K65
Anyone know of a better deal? on rock/mineral wool?
 
brian hall
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that link i posted for you is a ceramic blanket 1 in thick 2 ft wide and 24 ft long for $33 did you miss that?

where r "u" from i might be willing to split a 24 ft roll with you im in NC outside of raleigh
 
Pack McKibben
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Brian: I'm in NE Georgia... But I need more than that. My primary purpose is to insulate along a 14' wall, where the RMH and bench will be, as well as the heat riser and J-tube. I'm most likely going to buy loose fill from McMaster Carr. thanks for your help.
 
brian hall
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o i c thought you were just doing the heat riser.
 
Peter Peterson
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Hi Pack,

if you really want to save money and you are willing and able to work hard, you can mix clay (loam) with sawdust, form bricks of that mass and let them dry. Afterwards you fire them to more than 1000°C ( 1832 F). You need a kiln for this or at least access to a kiln. If this is not possible for you, you can build a kiln by your own out of the dried loam/sawdust bricks. After firing at least the bricks from the inner part of the kiln will be ok. The sawdust will be burned and the brick was transformed in a porous material with good insulating properties. You can reach densities of the fired brick down to 0.6 g/ccm tats not bad. Probably you have to make some experiments because loam is different from different sites. A recipe will not really help you because it refers to different loam.
If you try this, please come back and tell us about the results.
Have fun!
 
Pack McKibben
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Peter: I like your idea about using natural loam bricks. If I had time I'd do that. But I'm going to be working on this this weekend, so I'll most likely go with vermiculite mixed with clay/slip as my heat riser insulator. I've got some rock wool ordered from McMaster Carr for the wall area and J-tube.
 
Peter Peterson
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Hi Pack,
what about expanded clay? Here where I live it is cheaper than vermiculite. People use it for Hydroponics (growing plants without soil, the roots grow in expanded clay immersed in water).
Expanded clay is made somehow similar to the bricks I mentioned in the previous post, i.e. at a very high temperature so it will sustain the temperatures in a RMH. The insulating properties are worse than vermiculite but this depends strongly on how you use it. If you mix vermiculite with clay, i.e. you fill the space between vermiculite particles with clay the thermal insulating effect decreases considerably.
The deciding point is how much air you can trap in the insulation and how effective you can prevent it from convection.

Regarding Rockwool there is a video on youtube.com. Just look for “rocket mass heater – Autopsy”. Rockwool is good, but only for lower temperatures than the ones at a heat riser of a RMH.
regards
Peter
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Expanded clay
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Image found in the internet. It shows a cut through a brick made of expanden clay mixed with cement.
 
allen lumley
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Pack Mckibben : You may have a special requirement for insulating along that wall, but there are other ways of dealing with protecting your exposures, some of which
could get you a picture spread in 'Home and Garden"!

You can come off of the wall with vertical 2x2s and use a cement board faced with a film of Mylar, or heavy weight aluminum foil, there is also a Bubble packaging material
with a shiny aluminum face that can when properly installed with an air gap on both sides reflect back >85% of light and heat energy !

Cindy M. mentioned Roxul, which is one of the names its sold under !

A quick mention of the types of cement board now showing up on the market, There are now to different Formulatons OF A NON-PORTLAND CEMENT,with no Lime in the mix
to fail at high temperatures ! These are Geopolymer cements, and some formulations are safe to use in very high temp locations !

These cement/concrete boards are often reinforced with chopped fiberglass, and some few members are experimenting with placing these concrete boards down on top of
pavers set on wooden floors and building whole RMHs on top of them, so you should have no worries using them vertically, just check the label !

I Think Both 'Hardyboard' and most 'Backerboard' are of these types, but I have not done more than see them in a corner of my local builders supply !

Using Vermiculite, instead of Perlite you should use at least 2 Xs as much, and be twice as thick around the Heat Riser, -if you can't do that, do what you can, and plan on
an upgrade latter !

In an Earlier Thread I mentioned that you can off set the barrel,slightly from directly over the top of the Heat Riser and make a cooler side of your Drum on the side facing
heat sensitive exposures, always remember to build the off-set towards the side of the Transitional Area, or pre-build the Transitional Area towards the '' Warm Side!"

Peter Peterson I saw the video of an all steel RMH franken-clone failure that used S.S. and vermiculite,but not the one ? you are referring to, Could you post it here for
others to link to ? In the second picture you showed a cutaway picture of a mix of expanded clay, and cement, I know It was there as an illustration, it just begs to be
pointed out that if a ''Portland type " Cement were used, we would be dealing with a high temperature failure of the 'lime' in that class of cement. For the Good of the Craft!

Think like fire, Flow Like A Gas, Don't be The Marshmallow! As always, comments and questions are solicited and are Welcome ! PYRO - Logically BIG AL
 
Peter Peterson
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Allen: here is the link for the video showing how rockwool behaves as insulation on a heat riser.

I do not know how some people manage that the video appears directly here in the posted text.

What do you think about a heat riser like in the attached drawing? It is just an idea, I did not test it. It is cheap and should work fine. I am not sure the aluminum foil will last for long but something has to prevent mixing of the flue gas with the air inside the rockwool and save rockwool from being blown away.
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Pack McKibben
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Peter & Allen: I'm going out on the town tonight (yeah right..to a lecture). Don't have time to chime in right now. Talk to y'all tomorrow...
 
allen lumley
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Pack : Enjoy the lecture, if pete and i get busy we'll take it to a new thread !

Peter Peterson : I have complete Faith in Rob T. he is one of the good guys, I had forgot about his earlier build/failure, guys lick him are rare!It was only after his interior
ductwork failed that The flame front / blast effect had direct access, to the Rock wool which he stuffed in between the two layers of pipe and packed in by hand ! You can
see in the video at 55 seconds that the hand stuffed rock wool at the top of the Heat Riser, where it is unprotected by any metal is still in good condition, see below!

I am sure that Rob used a Respirator and Gloves to clean up that mess, I know I would !

In this you tube video here is an RMH with fire brick and then wrapped around the fire brick is another 2 inches of rock wool, held in place with woven chicken wire fencing
This is an Ernie and Erica Wisner build that I assisted on and the video was taken about 5 months later, and yes she really is Anal retentive enough to save all her fly ash,

The RMH, and the Rock wool is doing well, as of Ten days ago today, after 14 months, - 'www.youtube.com/watch?v=W3TwEhjTwb4'

I really like the idea of something cut to fit that was as reflective as Aluminum foil for the outside of anything else on the outside of the Heat Riser! I don't think you could
use something that thin without the heat stress/heat Shock casing it to fail!

Possibly built with interlocking concentric rings, stacked on top of each other about as thick as a brick, I have bumped up a Thread By Alistair Warburton -to make it easier
to find, look at his scetches starting at July 1st this year, other wise I like it fine ! For the Good of the Crafts, As always comments/questions are Welcome PYRO AL !
 
Pack McKibben
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Not having found Rock wool as of yet. Plan B: I've got lava rock and vermiculite. Which would be best for the heat riser. I'll be building the J-tube and insulated heat riser this weekend.
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Pack McKibben
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More input from you's: I am planning on using sifted sand and clay (thru window screen) for the brick mortar. I bought a pale of refractory cement too. Think I should add some refractory cement to my clay/sand mortar? this for the J-tube construction.
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Cindy Mathieu
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Roxul is rock wool in bats designed to fit between the studs in a wall. It is easy to work with and is almost self-supporting. There are various thicknesses. Order on-line at lowes.com and you can pick it up at your nearest store. Do you have a Lowe's nearby?
 
Peter Peterson
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Pack:
you wrote:
“Think I should add some refractory cement to my clay/sand mortar?”

You find in the Internet examples where people mix clay with cement (e.g. [youtube]http://www.youtube.com/watch?v=7ANMXGrxgnE)[/youtube]

I wonder if the cement preserves its properties if it is mixed with clay. If not, it is wasted. But it is difficult to say something without knowing exactly what type of clay and cement is used and what's the ratio. There are so many materials we call “clay” or “cement” or “firebrick” or “fire cement” etcetera. In addition to this, in different countries different terms are used for the same thing. Internet discussions have an inherent problem, you never know what exactly the other means.
The only you can do, try and tell us the result. Tell us as precisely as possible what you did so we can learn how to do it or how to not do it.

Allen: two questions
1. The RMH you mentioned build by Erica and Ernie. Is the rock wool round the heat riser held just by woven chicken wire fencing? Does this mean the flue gas can enter the rock wool?
2. In an other thread you wrote about castable core units (I guess you mean combustion chambers) that burn at 3500 F. Do you know from what material are this made? Is this suited for D.I.Y.?

Cindy: What material is used to cast the “Dragon heaters” combustion chamber? Is this suited for D.I.Y.? Or is this secret? I would understand if the recipe is not public. There was probably a lot of work necessary to find it.

regards
 
Cindy Mathieu
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Peter Peterson,


Cindy: What material is used to cast the “Dragon heaters” combustion chamber? Is this suited for D.I.Y.? Or is this secret? I would understand if the recipe is not public. There was probably a lot of work necessary to find it.


There is a range of refractory materials available. In general, the insulative ones are fragile/crumbly and the conductive ones are strong. We use 3 different ones at the moment. The burn tunnel is cast from a somewhat insulative, but still strong product, which we have found from only one manufacturer. It working temp is 2,600°.

The details of the burn tunnel casting were designed by Peter van den Berg; he also approved the specifications of the refractory product. The burn tunnels do not lend themselves to easy "one-off" casting. Moreover, we use a vibrating table on the molds as we cast. So, I don't think it is suited for D.I.Y.

We think the Dragon Heaters offer value because the burn tunnels are tuned so that you can get an excellent level of efficiency and emissions without experimentation. We have the equipment to test our systems and anyone can read the results on the Dragon Heaters blog.
 
paul carter
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Peter Peterson

If you go on to http://donkey32.proboards.com/board/3/rocket-stoves-heating there are lots of people casting batch boxes including me.

Also Peter van den Berg contributes a lot.

I have nothing against Cindy but I'm not in the USA so cannot get her products.
 
allen lumley
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Peter Peterson : I am a little confused here, Yes rock wool Is being used on the outside of heat risers by many people very successfully, If you read my last comment again,
you will see that on Rob T.s experimental build the inner metal stove pipe liner failed just above the exit of the burn tunnel, that failure allowed the HOTTEST exhaust gases to
attack the Rock wool and it finally failed, the rock wool at the top of the heat riser and about 2'' below the inside top of the barrel was almost unchanged ! Re-view the video
and at 55 seconds you see Rob T. showing you mostly undamaged rock wool from that location ! Rock wool wrapped around the outside of the fire bricks is never exposed to
the extreme temperatures within the heat riser itself !

I think you must be referring to my response to a gentleman who questioned my quote on the temperature it takes to melt glass, He quoted the temperature that glass is
formed for the first time from raw materials, which is around 3500 dF in some cases, This other gentleman said that I was wrong, that No rocket mass heater has yet reached
3500 dF, and he was RIGHT, however My actual quote regarded the much lower temperature that already existing glass will melt at, about 2400 dF, this is the resin that
recycling glass is such a good idea, it is done at a lower temperature using less energy ! IF that is the conversation you are talking about,clearly both of us were right, and I
am glad the gentleman asked for a clarification !

I do like the idea of a refractive coating over the rock wool If we can find high enough temperature stuff for that location, The Sketch you drew for a proposal of a type of
heat riser is interesting, though I do think that it would have to be made up in sections each a brick high and stacked, that thin, and tall I do not see it taking the thermal
shock ! Keep your ideas coming they fascinate me ! For the Craft BIG AL !
 
allen lumley
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Pack McKibben : Cindy M. is right ! Rock wool as a term for certain types of batting insulation, is out-of-date , probably do to a powerful sales campaign most
people in America think all batting insulation is fiberglass ! Call your suppliers again, and ask for Roxul batting insulation,that the clerk can punch into a cash
register/ computer and it will tell the kid where in the store, the number of 'items' on the shelves, sizes and prices, that the kids can handle !
 
Pack McKibben
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Peter: Expanded clay looks great. I may look for that in the future.

For now, after all these questions, I'm going to use .............drum roll please!
PERLITE!
I went to the local farm supply store, where I buy my vermiculite, to buy more vermiculite. Low and behold, a BIG bag of perlite was on the shelf!
I EXCLAIMED...."YOU HAVE PERLITE!" .....oh, yeah, from time to time we have perlite. I bought some to use for my heat riser.

I'm going to order some of that ceramic fiber blanket from McGills (thanks for the link Brian) soon to use between the 8" stove pipe and my Clay/straw wall....

I'll be taking pictures to post as I go along.

Thanks Allen, Peter, Cindy, and Paul for all your help...but hold onto your seats, I know there'll be more Q's to come!
 
Peter Peterson
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Paul Carter: thank you for the link!
Cindy and Allen: thanks for your answers!

Allen: I agree with you regarding the video of Rob T. I stopped it at 55 sec and you are right.
I also belief that a heatriser made of fire bricks wrapped with rock wool will last for long time because the rock wool will not be directly hit by the flames, as you say.
In question no. 1. (see my last post) I meant the flue gas flowing downwards between the heatriser and the barrel. At this place flue gas is not hot enough to melt rock wool.

Why did I ask question no. 1. ?
Rock wool is thermally insulating because of the air trapped between the rock fibers. The fiber itself is not insulating. It has a similar thermal conductivity as the rock it was made of. The task of the fiber is to prevent air from moving round (convection). Moving air would transport heat from hot surfaces to cold ones. This means it would be better if the layer of rock wool would be enclosed in an airtight coat to prevent any air going in and out the rock wool layer. That's one of the reasons (besides reflection of thermal radiation) I drew an outer layer of aluminum foil in the sketch. Ok - this effect might be small. If the rock wool layer is thick enough there is enough air in the middle of the layer that can not move anywhere. Regarding the heat riser of E+E you mentioned, on one side of the rock wool layer there are the fire bricks, so this side is closed. Only the opposite side, where the wire mesh is, is open to gas exchange that lowers insulation. In practice this might not cause concern.

best regards
Peter
 
allen lumley
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Peter Peterson : If you want to see some super efficient insulation, search aerogel at Wikipedia, and then spaceloft ! Developed by N.A.S.A. there seems to be little
interest in driving down the price on this great stuff Big Al ! !
 
Peter Peterson
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Allen: Yes I heard about this. If the bubble size comes in the range of the free path length of the air molecules, the thermal conductivity drops tremendous. But this is nothing for us poor D.I.Y. guys
 
Gus Mccologie
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In ceramics the bricks used to build kilns are called firebricks and have different refractory ratings. There are also "hard" or "soft" bricks. Hard bricks are very dense, and are used for the interior to retain heat and slow cooling, and for chimneys that will deteriorate faster for various reasons. Soft bricks are very light due to a lot of pores and are used mostly for outer layers and insulation properties. It is very easy to make a mixture that duplicates the softbrick by buying dry material 50-70? bags of fireclay that masons use in bricklaying. ($10 or so ) It has a very high refractory value. Combined with sawdust, sand or vermiculite and cement you have a mix that can be made into any shape. The cement will lose it's structural strength once fired- it is added at a low percentage 10% or so to facilitate building because it makes the mix set, and there is no wait time or slumping from the weight of new material being added on top if you are building thick/vertical.
You can also make your own bricks or units to build with. You could do that with just clay and sawdust if you let them dry first.
I built a bottle kiln using a similar mix as the insulating layer with my local clay boosted for higher temp limit with some bags of fireclay, road sand dug from the ditch in spring, large particle loose vermiculite -the type used as blown in insulation, and sawdust. And the cement to set it up as I went. Somewhere I have the formula, but it was pretty loose as I knew my clay(soil) was pretty stable for my needs. If anyone is really interested I could look it up.
Hope that helps- it's a very cheap and easy solution!
Also Stonewool and expanded pellets have about the same heat point; over 2000 degrees F, but the insulating wool for building is very different than the horticultural medium type- it has a binder and is infused with oil to make it water resistant. I don't know how the burning off of all that would affect it structurally, (I doubt in any way that make it melt thereby compromising it) but it would probably smell really bad, at least at first so something to consider...
 
allen lumley
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Gus :Thank you very much for this post, I hope we can ask you to add more, your experience and Techniques could allow us to bridge several gaps, generally when I need to
encourage someone to do research on materials so that they can learn for themselves I send them to- ' www.traditionaloven.com/articles/ ' -There is in my uninformed
opinion a good set of You-Tube tutorial videos by a English(?) Potter named Simon (?) Could you add a few outer sites that you have found basic but simple ?

At the temperatures we can produce easily 2400dF we have seen Concrete pavers explode, and when new builders have failed to insulate carefully enough we have seen the
spalling of concrete floors, Generally we tell every new Fellow member to never use Cement because of the failure of the Lime in Portland type cements that start at 400 dF
and is guaranteed to fail with time at 600dF !Am I correct in understanding that you have experienced No catastrophic failures of your mixes with Portland cement Mixtures of
only 10%? And that you do expect the lime in the cement to fail and only want the cement there to temporary stiffen the batter/mix ?

I understand that there is not just one right formula that will work for everybody, actually we try to tell every one to be quite particular about the type of sand they are getting
we tell our members to get sharp sand, which may cause some people to think of the sand in pool filters, or diatomaceous earth, but we want what is also called Builders or
Masons/masonry Sand !

I do also want to clear up one more point for any fellow members who may have missed that in your explanation of Hard and Soft Fire bricks, your described placement was
correct for inside a kiln, In order for us to first Pyrolyze wood and burn the wood with near 100% efficiencies, we need such high temperatures, > 2000dF that we place our
soft fire bricks on the inside to line the Combustion chamber, making care to protect them from rapid wear due to friction! The harder brick is carefully placed with additional
insulation to protect exposures and hopefully prevent Thermal Shock damage !

Please excuse my seeming nit picking, on the grounds that this is new information to your fellow members, and not always regarded as fun reading ! For the good of the Craft !
BIG AL
 
Gus Mccologie
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Re: to Al- Comparing kiln building and RMH is really interesting. There's the practical technical science, but then the adaptation of available materials aspect that is very similar in both groups. Plus no one wants to build something that melts down (seen it) or has the fire department breathing down your neck (been there), Of course saving money and recycling where possible is one of the appealing aspects of both to me.
I can really only relate my experiences and observations in firing and kiln building to what people are doing, fire being fire and all. Between college/work/personal experience I've fired or help build about sixty kilns of all types so a broad range. There is a lot of cross over, but a lot of differences too.
I looked at the link you posted. It has good info. But. I know a few people who have made bread ovens- all potters, all data junkies with stop watches, pyrometers and kiln logged tests and the temps are 1000-1400 tops. And compared to a kiln or RMH firebox, more open...cooler burning, although I don't know by how much. Point is not as intense. Also short burns, and much less fire/wear time. So I don't know how helpful for referencing RMH's.
On the other side, kilns are usually built with one potters clay, glazes, and firing temp as driving design considerations. It's about efficiency and cost of firing in relation to the product, both in individual firings and life of kiln.
Ovens and kilns have the same purpose. Raise the temperature to a desired point, then shut it off and let it cool. In the kilns case, as slowly as possible. RMH's are a bit more like a forge or glass furnace for the sustained length of generating heat at such high temps, and using the rushing air as an accellerant.
The potter you refer to Simon Leach? possibly? If so I actually met him- he was on a workshop circuit in the early 90's and did one at Munson Williams in Utica. (near me). Hate to admit it, but I'm not familiar with any kiln-related videos he did, will check it out.
As to others to look at, I think sustained wood firing would come the closest in concept. Especially anagama style kilns; historically and their modern equivalents. And there's as many different opinions and variations as with RMH's but going back to ancient times! US southern groundhog kilns too- also use the earth as mass.

The cement in any mix would definitely not contribute to strength other than when wet as a stiffening agent. Even without any breakdown from heat, 10 % is not anything. Nylon fiber would add more when it's dry, which of course would burn out and be no help when wet. I would not use (any) cement in any mix for the hottest areas. At 2400F, especially in the absence of oxygen, the cement could act as a flux and combine with the clay in the mix and lower the heat tolerance significantly. You can definitely make your own soft firebricks with sawdust but you need use a known fireclay or do very good testing on found clay. Most mixes I've seen like I described are over arched kilns etc. With mine, I had a generic furnace firebrick liner (on their sides for economy!) and my interior temp was max 2150F b/c I was firing local clay and that was it's limit. It was an insulating layer between an outer scavenged mix of red bricks for protection from the elements.

More on real bricks; firebricks (hard or soft) are rated for temp limits. Especially important under their own weight because if overfired will start to melt and slump. They are basically high alumina large-particle clay that doesn't expand much. Here's a good chart for reference: http://www.sheffield-pottery.com/SOFT-BRICKS-Insulating-Firebrick-s/372.htm Look at the Si:Al ratio for each temp increase. You can similarly get the breakdown on any dry bag of clay you might buy to make your own mixes. Different clays are available in different parts of the country, although you can ship anything. But there's only a few types so regional is fine if it meets the specs you need. In addition to masonry suppliers, potters or schools/colleges near you may order regularly and you can often combine shipping to save if you want to order in bulk. Some found clay is fireclay. More found close to the surface is earthenware which fires red, and contains a lot of different impurities that basically melt it into a glaze at anything over 2000-2100F sometimes a LOT lower. Think of the old Albany slip that was used on antique crocks as a liner glaze. Fired lower as a lump it would be a brick. If that brick was heated to the stoneware temp used in the salt kilns the crocks were fired in it would melt into a puddle. This chart could be useful too for people trying to get a grasp on temperatures and supplies: http://www.ceramicstoday.com/cones.htm There are recipes around on various pottery sites to make your own kiln furniture. Posts, specialty supports even shelves. Not at all difficult. Probably worth the effort for a few to go in on together if planned out well.

My own next question would be, Why use brick at all vs steel as some I've seen to line the Combustion chamber? Seems expensive. What creates the wear and breaks it down? What do you mean by protect it? Is the softbrick to prevent a buildup of heat within the barrel so it pushes more into the mass? Again, I've seen some that look like they are using hard firebrick... do their barrels put off more initial heat into the room?
Also why does the sand type matter? For sharpness or mineral makeup?
So many variables to take into consideration!
 
allen lumley
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Gus : Expect a P.M. From Me ! Yes it definitely was Simon Leach, I am sure that none or very few of us think in terms of glass furnaces,
just about a year ago Ernie and Erica Wisner were doing a workshop in Montana, and Erica had built a industrial soup kitchen model that
a little ego and a little egging on lead to a head to head cooking time contest with one of those whole-turkey-frying-oil-bath, too-loud-
to-carry-on-a conversation monsters! Time, and a few modifications later (running only on very dry hard wood ) They had internal parts
running at metal forging temps -so of course a few twisted shaft fire place pokers were run up on the spot ! So yes, we can talk about
forging as a comparison ! Also the warping and carbonization and failure of even stainless steel, bricks rule, steel drools (and puddles )

Sustained wood fires kinda, with soft fire brick and super high temp refractory /ceramic blankets wrapped around the soft brick we can
easily maintain high enough temps using very little wood, (the inside dimensions of a Rockets combustion chamber on an 8'' system is
only 7'' by 7+'') with the previous wood nearly consumed in say an hour, and the sound of our rocket losing volume, we can expect to
look in the feed tube, and bathing the remaining embers find a (visible in daylight ) red glow from our bricks, at this point new chunks
of wood 'fed in' seem to miraculously burst into flame! I thought anagama was the name of a Bread made with more than one type of
whole grain floor Southern groundhog kilns have much in common with fox fires, or foxhole fires, and date back at least to the early
kilns designed to burn pine and collect ships tar (creosote ) and turpentine, local descendants are still called tar heels !

With cement, I was pretty sure that your answer was going to be, but as always we are leaving a trail for others to follow so I asked for
clarification, certainly in the reduced oxygen concentrations found in the RMHs Heat Riser we would see a flux forming if someone tried
to use it there, generally we say that 'The Lime starts to fail!'

Bricks, the Sheffield prices on the chart you sent me seem pricey, friends out west are quoting me $1.50 each, with no mention of
shipping charges, is there that much of a break for lots/pallets of bricks of 500 ?

About 3 weeks ago I tracked down retired SUNY Potsdam Prof. Art Sennett and picked his brain for local clay deposits, -what I thought
for years was dense hard clay was some kind of silt masquerading as clay, and everything else I can find is Blue, or blue grey, which
apparently gets disregarded on sight (for lack of alumina?) Though he could not help me pinpoint any good clay close to home, he was
a very interesting man to talk to, our Discussion about Albany Slip was that when electrical and telephone lines went from pole to pole,
the insulators they met were coated in Albany Slip Glaze !

We covered the fact that steel does not hold up the high temps as well as brick, there is an old saying that to a man with a hammer,all
problems are nails ! If you have welding experience, building a wood stove out of steel Can make sense, but we are not just building
wood stoves, usually the first thing I tell want-to-be rocket builders is stop watching You-Tube!!! (unless I send you there !) One guy
builds a Frankinclone RMH-like device, and puts a video of the build on You-Tube, and says 'look what I am doing ', six months later the
video is still up there, but all comments are blocked or are 4 months old but Now there are one hundred more 'Look what I am doings',
and the original builder has lost interest, and is off chasing the next shiny bauble. Ask all of them in two years about that rocket stove
thing without mentioning the video and the answer is ''I tried that, they don't work " ,'' Those crooked brick markers are getting rich''

Most of the wear is due to people dropping wood in or trying to twist and press in one more chunk, but in this location emissivity, or
the material that makes up the walls of the burn tunnel's ability to re-radiate that heat back into the combustion zone is damn near all
important !

Wear is caused by general ham handedness. There are two other opposing forces here, the boundary layer of still air that can exist at
the surface area of an object, Usually called Laminar Flow, for us it should be called Laminar No-flow, And also the scrubbing effect of
high speed air and turbulence!

We insulate the combustion chamber and the heat riser ascending to the top of the Barrels interior to promote draft,and then a Miracle
occurs, actually as you know energy has to be used for work to be done, the shedding off heat off of the totally uninsulated barrel is the
work energy or 'Delta T' to an engineer, put more basically the hot rising air pushes and the rapidly cooling air rapidly sinks, push me-
pull you! This allows us to flow the still hot exhaust gases, 40 ft horizontally through our cob thermal mass bench ! Temperatures for the
exhaust of a well built RMH at the base of its terminal vertical chimney are in the 150*F range ! I totally understand that you are used to
loading heat into hard fire brick to insure that Your kilns firing temperatures remain constant, and it is easy for the eye to see what the
mind wants it to see !

Initially I had thought that the ratio was as low as 30 % of the heat radiated into the room, but I am adjusting my thinking upwards to
40%, possibly higher!

Sand, we say that while sand is the glue the sand locks up the clay and reduces the amount/percentage of expansion and contraction,
like grog, and you don't use round spheres for that ! And masonry sand gets its name from the practice of using just sharp sand and
something close to fireclay 60 ! For the good of the Craft ! Big AL !
 
Gus Mccologie
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Al- Thanks for all the answers!
Didn't realize I was linking to all those specific bricks; it was really for the data chart with the temp limits and Si:Al ratios to compare to clay analysis....

I am confused a bit by this thread. I have mostly seen combustion chambers with brick as the innermost layer insulated with perlite/rockwool etc. around it contained by metal, (and some not insulated at all) but then others with the rockwool on the inside, like the posted video here that would be in contact direct with the fire. Doesn't the heat stored in the brick help keep the temp up to facilitate a cleaner burn?

 
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