Drawings for 8" system in wood house

Hello everyone. I have enjoyed looking through past discussions and photos of rocket heaters on this website, and am now preparing to build one of my own.

-The plan is for an 8" system based on the book by Ianto Evans and Leslie Jackson.
-I have an exposed dirt basement with seemingly good clay soil I plan on using for the cob. (I did a jar settling test, and snake test. Yet to do a brick test with different sand contents).
-I have broken concrete for the bench.
-I have a 55 gallon drum for the combustion unit.
-I plan on a light sheet metal heat riser with clay slip-perlite between the two layers of metal.
-I plan on a cast core of cob and fiberglass strand instead of brickwork.
-I plan on purchasing a sloped roof chimney kit and installing the chimney in a vertical run from it's exit on the bench.
-I will be able to add extra support under the stove and bench.

I am posting these drawings for anyone with experience in these types of things to comment on. (Feel free to make fun of my spelling of the word vertical all you like)

One thing I am unsure of is the specs of the bench. I currently have it drawn with the ducts touching each other in the very center of the bench, with the intention being to keep them as far away as possible from the surface. What has me a little confused is a reference mentioned in Ianto's book about keeping any straw in the cob at least 6" from the duct work. With any reasonably sized bench, this seems impossible. Will I be fine with the straw\cob layer 4" away from the duct work? I already feel like the bench is as big as possible for the room (my families main living room) at 20"x 24" including a 4" airspace on the bottom.

Also, is 26' of duct work less than I should have? If it is worth it, I could find a way to get that a bit longer. If not, it fits the room nicely this way.

Is the 8" HVAC duct that is sold at Home Depot ok for the duct material? I ask because it is galvanized, and I have heard that smoke from galvanized metal can be toxic. I would love to use it if it won't be an issue, but could spend a bit more on painted stovepipe if I have to.

Vincent Musser : Welcome to Permies.com and a Big Welcome to the Rocket Stoves Mass Heater and the Wood Stoves Forum/Threads!
With over 18,000 fellow members you will always find someone here who wants to talk about what you want to talk about, here you will find widely even
wildly different opinions discussed, usually clearly and politely !

I am very afraid that a cob only Castable core will be too soft with or with out reinforcement , and while the melting point of silica the main ingredient
in glass has a high melting point, manufactured glass and to a great degree spun fiberglas has a much lower temperature ! Cheap re-cycled soft Red brick
will be a better Feed Tube, Burn Tunnel, Heat Riser base than anything made out of cob !

Lets deal with the stove pipe, Because of the number of elbows you have in your system, I agree that an 8'' System will work best! I want to send you to
our sister site richsoil.com- click on and go to the rocket stoves section, there are a set of videos and you should watch all of them. Specifically I want you
to see how we prepare the 55 gal drum and 1st 5' of stove pipe. This burn cleans out the inside and out of the barrel and vaporizes a small % of the total
zinc galvanizing on your stove pipe, the rest goes thru a physical change in the way the galvanize bonds with the metal of the barrel, this is a safety step
that should not be skipped, and is your 1st burn of many, that will give you a Rocket Mass Heater and your own personal house Dragon!

A few recommendations, because you are building your R.M.H. above your wood floor you have subtracted the thickness of a brick from the volume of your
Cob Thermal Bench from below, this is why you cant seem to get deep enough. I am going to recommend you remove even more material but 1st you must
know why !

I want you to go to ernieanderica.info/arrange-a-workshop/site-planning This is a great D.I.Y. / R.M.H. building guide that will take you through your
build step by step, assuring you that you have completed your ground work and have all the materials on hand before the build ! This guide was originally
made by Ernie and Erica Wisner to make sure that the people they helped under stood the steps of the build, while you are there, you should take a look at
the sets of plans available, you will quickly identify the set of plans that are right for you !

Because of the weight of your Thermal Bench you will have to brace your floors from underneath ! A simple 'cement pad' in the basement and a few posts to
brace a horizontal timber will keep the floor from settling which will crack your monolithic poured Rocket and Thermal Mass !

These are all very small set-backs in the grand scheme of things ! Remember why you are on this journey, remember that Cob will not burn or rot, insects
will not eat it, and It is as Cheap as dirt ! And so are rocks and urbanite ,there is a R.M.H. in your future if you want on ! Good Luck !

For the Craft, Your questions and comments are solicited and Welcome ! Think like fire, flow like gas, Don't be the Marshmallow ! PYRO - Logically Big AL !

Allen, thank you for your detailed response.

I was thinking of the cast core for these reasons:

1. For the insulation value (perlite mixed in)
2. Ease of fabricating to exact dimensions
3. Prefab, make in my shop, bring inside and build around it. I like that.
This video is what pointed me in this direction:
http://www.youtube.com/watch?v=7ANMXGrxgnE
Have you seen it?

I watched the videos you directed me to, and will follow the "first burn procedure".. looks good.

I also had a look at Erica and Ernies site. They are great, aren't they? I have enjoyed lots of indirect help from them already, both in their comments on this site, and the videos they are in explaining things. (and a podcast I listened to a while back!)

As far as intentions for the build, I have a few:

1. Heat my house for less money
2. Stress the environment less for my comfort needs
3. Put something ALL natural into my house.
4. Gain experience in natural building techniques, as I would love to eventually be more involved in natural building in my career. I am a home remodeling\repair contractor, and I will say that I don't get to deal with natural materials very often during work.
5. Build something profoundly meaningful right in front of my two young sons. (5 years old and 3 years old) They will be able to see how it works, and I already know they enjoy going into the basement and chipping at the walls.
6. Experiment with my living room, while not being locked into anything permanently. (Seems like one of these could be chipped up and thrown out into the garden in a single day if the need came). While I do own my house (or at least the loan on it), I still love the idea that this is so much less permanent than say, a masonry heater.

On the bench, as I am in the planning stage, it has changed. I want to put a back rest on top of it, as the bamboo couch we currently have in the proposed rocket mass heater spot has one and is a proven perfect fit for spending time on comfortably. I thought the back rest could be tied in with cinder block "splints" placed inside. I think the bench will be more pleasing to the eye with this addition as well.

I am going to recommend you remove even more material but 1st you must
know why !

Why would I remove more material? I was thinking if anything I did not have enough mass to store all of the available heat of an 8" system.

Bracing under the floor framing was planned for this project. The proposed location for the heater is over easily accessed crawl space.

Vincent Musser : O.K. we have knocked the bigest problem in the head right off of the start ! While the furnace cement does have a function for good ability to bridge
rather wide gaps/cracks, here it seems to increase strength of the final material, So Include that in your Core's build.

Broaudio = 'Bro Audio' goes by another name here in the Rocket/Wood Stoves Forum/Threads, and has a few more videos as a series, have you seen them ?!

In this case he talks about fire clay, which is a kind of misnomer, So-Called fire clay has a small maximum expansion rate when heated and thus is less likely to
crack as it goes through repeated heating, cooling cycles, when 'fired' - - Kinda like the old New England whalers picked out a species of whale and called it the 'Right
-Whale' because it was the right whale to hunt! Your clay out of your basement should be just fine, as a contractor I'm sure you have access to good gritty builders
sand, it also serves to check the amount of expansion contraction your clay can 'get up to ' !

As you have drawn your last picture the cement backer board should not be trusted to support the weight of your cob bench , Turn your bricks to be at Right angles
to their present orientation, so they are running across the floor joists, not parallel to them , This is where I would then cap them with 1' square pavers. If you already
have enough pieces of backer board I would place them directly on the floor, apply a radiant heat barrier and build on that !

With this smaller gap, and 2 layers of Cement backer board you might have enough material strength needed for this installation. Cob is Heavy! Both the floor and the
top of the pavers that you will build your Rocket and Thermal Bench, should be topped with Refletx foil or sheets of heavy Aluminum foil! Just glue it right down, and
protect it during your build !

With the bench back that you are planning, you should have a natural air flow across the floor and up the back of your bench, this last area should be protected by the
air gap you were already planning on, With a reflecting/radiant heat barrier and small air gap with minimum bridging !

Unfortunately we are not done yet! You will need to plan on at least two inches of a perlite only or perlite clay slip admixture to allow you to retain your heat within
the Rocket stove and first 6-8 ' of your thermal bench, Remember that the lime in regular cement will be degraded by temps over 400 F !

While we have been raising your rocket mass heater off of your wooden floor for safety, we have just been raising it up into the air, I leave it to you to create an
attractive single or double set of steps and / or foot stools that will not block the natural air circulation you are trying to create !

You can do a little research Via the Permies tool box at the top right of the page, click on Search, scroll down the new page, and do a google search within permies for
a castable core, as I said bro audio is a regular contributor to these Forum Threads, I am sure that he would like to hear from you about your build, and will respond to
a PM.

While Rocket stoves and Thermal benches are infinitely rebuildable, You will find that as a monolithic pour they are very strong. especially after you add straw to the mix,
a major rebuild with demolition will probably require wrapping the affected area in Wet burlap and plastic ! Minor mostly cosmetic cracks need only fresh clay slip and a
paint brush !

Re-reading this it comes across much more negative and bossy than was my intention, and for that I am sorry, rewriting this again is probably futile, take this free advice
for what it is worth! Hope this Helps, For the Good of the Craft !

As always all comments and questions are solicited and Welcome ! Big Al !

Vincent Musser : You may have noticed from past comments I have made that- there is so much Jreck out there in You-Tube Land, that I do not spend much time there.

However, I just found a Different video of ''Rocket Stove classroom instructions with Ernie & Erica Wisner", www.youtube.com/watch?v=3mZQdu2wNi4 This is a
new find for me and I have just browsed through it, but this should help you see both an early build on a concrete floor where E +E were personally going to live and a
later build on an existing wood floor, with a wooden stud framed exterior wall !

At 35min and 40 sec -, 35:40 to 38:37 Is a '' still picture '' from the Step by Step build recorded by Calen Kennett, the picture clearly shows the air channels completely
underneath and through to the backrest. On top visible as individual shadows, are the inset registers that help promote the air flow! This is the only Kickstarter DVD Video
that shows a Complete 'Conventional R.M.H. build' ! ( Not the one that comes as a 4 DVD Video Set )

The pictures from ~ 38:40 are of an Earlier Build -Erica calls it their Honeymoon build - the cooler pipe is against the outside wall, and there is a gap filled with perlite
between the outside of the bench and the inside of a poorly insulated exterior wall ! (~ 53:00min~) It is my understanding that eventually the Rocket Mass Heater R.M.H.
as a standalone was later certified as Code in Portland Oregon with a wink and a nudge on the Thermal Bench.

Hopefully if a pictures worth a thousand worlds, you will have a better idea now of the rather small changes you will need to make to have an R.M.H. that will be an 'A+'
build giving you a great return on your investment, and something that will quickly develop 'pride of place' and be a show piece that your whole family will be glad to
show off ! For the craft !

As always, your comments and questions are solicited and Welcome ! Think like fire, flow like gas, Don't be the Marshmallow ! PYRO - Logically Big AL !

Allen,

I am still sold on the cement board for a few reasons:

1. I can cut the "foot print" of the stove and bench with contours. I enjoy building curves, but like to be able to keep pretty precise as I a progress on something like this. I finish drywall often, and even, straight planes are a love of mine, even within curves! (If that makes any sense)

2. It is less thick than pavers.

3. Less expensive than pavers.

4. The bricks are intended to be installed perpendicular to the floor joists, just didn't show that correctly in the drawing. I figured I can put bricks in this pattern as close together as needed to support the cob until it is dry. Once dry, the cob will be a self supporting unit, able to bear it's own weight with concentrated bearing points all along it (bricks foot print).

I want to try not having a step in front of the bench. I think it will jsut have to be a 20" tall bench. Maybe I should set the bricks on the edge that lowers them the most. I think that would be more like 2.5" airspace?

I watched the video of Erica and Ernies clinic.. very helpful. Yes, seems like they had the backrest up on some wood slats or something for airflow? But they didn't mention it in the presentation..

Yes, I will need to source some furnace cement for the core.

On the sand, I was just planning on picking up a load from our local concrete and gravel supplier. The kind of sand that masons use for mortar is appropriate, right?

Test bricks

Vincent Musser : In no special order, broaudio = Matt Walker =broaudio, there is a good Forum Thread 'A Castable Core " which I will 'bump up' so you can find it !
I am worried that there is not enough insulation under the 'Core' For installation on a Combustable wood floor, I would build with added insulation any way, -Just
Check with Matt Walker before you do an install !

Working finishing sheetrock gives you the mindset that good sharp corners are the mark or a craftsman, Been there Done that ! Having said that -

There is a reason that port holes are round. As a ship works 'in a sea' Metal fatigue will show up at the right angles with cracks and 'skin tears' .

"Mud Architecture houses'' regardless of the culture they sprung from- all have rounded corners, - if you ask the person from that culture 'why ?' They will tell you
what their Grandmother said " So the Devil has no place to hide ! " ! Same answer (mostly), same rounded corners ! It just makes for a stronger build, I always
build-in sweeping curves working with Cob, and I think I would rough sand the exterior corners on my 'castable core', I wonder would dry wall tape stick to backer
board well enough to allow you to cast in slight curves into the very ends of the floor of the 'castable core' ? - Anyway, don't let your craftsman's eye for a sharp
straight line get you in trouble where a curve is stronger !

Weight ! You are planning on your Thermal benches monolithic pour coming in at around 4-5 Tons right ! My addition of 'The book' has the specific information on
pages 25 (Thermal Battery ), and 62, ( floor bracing sketch ) I worry about your backer board even at 2 thicknesses holding up to the weight which will be at right
angles to any designed/built in strength , But I know next to nothing about its load carrying capacities ! I have certainly given you something to chew over !
Hopefully this helps a little. For the Good of The craft ! Late Note : You have to cute boys, congratulations, you must be proud !

As always comments / questions are solicited and are Welcome ! Think like fire, Flow like Gas, Don't be the Marshmallow ! PYRO - Logically BIG AL !

Allen,

Thank you for all the advice, and friendly, helpful attitude as well!

I will read up on that thread before my next post..

I will make sure to have a radius on every corner that is on this beast. That said, I hope to be able to keep them consistent!

I am working on getting another drawing up here that reflects some changes in the duct spacing and brick orientation. Most likely will be up tonight.

I am imagining cob to dry into a self-supporting "block" of 23" wide x 18" high. With the cement board under it, up on bricks on front and back, I cannot really imagine how it would fail. Maybe casting some rebar into the clay\perlite mix would help. I will show all this on my next drawing.

Note: One thing that was in my head more than actually written down anywhere was this:

I was planning on bracing the cement board in the middle of it's span while the cob is setting.
I think the part that I did not convey adequately was that I think of the cement board as a temporary mold in which to cast cob, that can be left in place afterwards, due to it's fire-proof nature. So I don't expect it to do any more than plywood, structurally. The only benefit is the ability to leave it in place as a permanent part of the stove\battery after all is set and finish over with earth plaster.

V. M. : o.k., cool - i think I understand better I was starting to sound like a broken record to myself, and just wanted to make sure we were on the same wavelength !

Looking forward to the pictures ! Big AL !

Next draft..

Made the bench much deeper. It is now drawn at 35" front to back, and 18" high seat from the floor.

Would not having an ash pit be a huge problem? Seems like there is not going to be any easy way to have one..

Vincent Musser : For your clean out Do the best that you can , the best 55 gal barrel is the kind that has one end that is completely removable with a clamping devise to
hold the top in place.

You burn out the barrel and several feet of your galvanized pipe , remove your solid end of your barrel and that becomes the end that gets mated with the cob and sealed
in place! Then when you want to clean out the fly ash you pop the top off of your 55 gal drum and clean up with a shop vac!

If you go to our sister site,richsoil.com and click on Rocket stoves you can see this set-up in the home Ernie and Erica Wisner are living in now ! For the Craft !

As always, comments / questions are solicited and Welcome. Think like fire, flow like gas, Don't Be the Marshmallow Big AL !

Ahh, clean it from the top, no ash pit needed.. got it.

My barrel does have a removable lid, but I was contemplating doing the extra work to use it that way. Now I have a reason.

I am wrapping the barrel with clay slip and newspaper right now, getting ready for the first burn..

Thanks

V.M. Remember to save 1 1/2'' - 2'' for your structural cob, the stuff with the straw, and your final waterproofing finish coat ! Big Al !

Bello Vincent and Allen,

Like you can see in the video http://m.youtube.com/watch?v=4usXIAoy9us of Paul, it suggests that E&E can remove the barrel by unclamping it. Two barrels attached ( clamped ), of which one barrel partionly used and embedded.

Would be easy cleaning. And makes it possible to skip the first clearance ?

Warm Regards Johannes

Johannes et al : I am not actually promoting the none use of ether a clean-out or an ash pit, in fact I will make sure that I include this in any of my future builds!
however i will admit that if one has the type of barrel with one end removable and builds accordingly - and has access to the grid for power and a shop vac, it is
possible to make a planned build where this can be a secondary consideration ! For the good of the Craft !

As always your comments / and questions are Solicited and are Welcome ! Think like fire, flow like gas, Don't be the Marshmallow ! PYRO - Logically Big AL !

allen lumley wrote:V.M. Remember to save 1 1/2'' - 2'' for your structural cob, the stuff with the straw, and your final waterproofing finish coat ! Big Al !

Do you mean in general, as I never showed these layers in the drawing? If so, I was just planning to have the outermost 1.5" of cob on all the surfaces to have chopped straw in them. This refers to the outline of the bench\cumbustion unit shown in the drawings.

Then, I was planing on adding 1\2" of earth plaster to it all when the rough cob is finished. Didn't show this on the drawing, but I expect it to "grow" 1\2" more all around once finished and lime-painted.

Also, I am planning on using "form boards" to build this thing. I want to use 1\4" plywood and templates to shape it all. Will this create any problems for the earthen finish plaster adhesion? I wonder if cob with a plywood formed surface could be to smooth for earth plaster to stick to. If so, will scratching the surface of the structural cob be enough to promote earth plaster adhesion? (One of those worries that won't leave my mind all day)

Thanks

Vincent Musser : I think you have the idea right, each layer of cob should end up with lots of surface area, think what the bottom half of the container for a dozen eggs looks
like, ether shaped as you go, or using a 'Cobbers Thumb' between layers of cob, then paint on a thin layer of Clay slip between layers to re-wet the old Cob and glue the layers
into 1 solid monolithic construction. Use a paint brush and cover everything that you want to Cob,or use Cob to seal (bottom 1/2 of Barrel )!

If you need more info I would have to refer you to Evans' et al " The Hand-Sculpted House", and M. Smiths ''The Cobbers Companion'', nice books to have, maybe put them on
a wish list and leave your computer on !? Hope this helps ! Form boards, I have used for concrete only ? your form will have to be quite stiff, flexion will create a 'patty cake'
effect = bad, Rubbing and stroking to achieve a hook-up between layers and mixed materials = good For the good of the Craft ! Be safe, keep warm !

Comments and questions are solicited and are Welcome, think like fire, flow like gas, Don't be the Marshmallow Pyro - Magical Big AL !

Vincent : Please forgive me for finding a small potential problem and growing it ! Your Sand and clay bricks look like they could contain a little to much silt ! If you look on line-
what we are talking about is sometimes called a Soil settlement test or a Soil sediment test, or a Clay settlement test or Clay Sediment test. Ianto Evans in his book 'The Hand-
Sculpted House' simply calls it the 'Shake test'. here is a paraphrase-

With several quart jars, a gal of water,and soil to test for clay, fill the bottom 1/3rd with soil(lumps if any carefully crushed), fill to near top w/ water. add some salt or 'soap',
shake long and hard, -

At 5 seconds. sand, pebbles settled out, mark the side of the jar, at 10 minutes all fine sand, silt settles out, mark the jar, Clay can take a long time to settle when the water
clears above it most of the material in the unmarked higher area is clay, now you have a clue as to the ratio of Clay to silt, it just seemed that your bricks looked like they
shed sand a little to easily !If low on slit it was all in my imagination ! Big AL !

Allen, I have done this test twice, with the jar and water. Both times it has taken a good 12 hours or so for the majority of the material to settle. I will play around with it a bit more just to make sure. I think most of the sand from those bricks was coming off the higher sand ratio ones. The one that I used 1\4 sand to 1 earth was pretty tough. Then it went the whole way to 1 to 1 and that was very crumbly. I will test more though, with larger jars. I had been using a small amount for the jar test.

Just did the test with a masons jar. Here is the photo after 10 minutes or so. Arrows indicate first heavy sand, then the lighter sand that came down after 10 minutes. I am guessing all the water-born brown is clay?

Here it is now after 10 hours. Looks like about 1\4 clay to accumulated sand and silt. I know from my test bricks that any more than 1 part builders sand to 4 parts of this earth becomes crumbly. I think this stuff is right on the edge of having a perfect ratio dug right from the ground.

I had about 1\4" of newspaper\clay slip on this barrel. It popped off after maybe 10 minutes of hard burning. I had the rocket effect going for a bit with the old duct I threw in there.. first time to hear it in person! Baby, I'm ready! Sounded nice.

Vincent Musser : It looks like your burn came out very near perfect, I would have liked a lot less Silt in your Clay but- the answer is that when you pick a spot
to dig that is disturbed earth, This is what you get , We need to change gears a little and find out what suits you better a pith helmet or a deer stalkers hat !

Bones, or Sherlock Holmes! You will need to do some surface exploration, followed by an Archaeologic Dig ! With your other half's acceptance you will need to
peal back the sod in an area say 2' by 4' and then dig, the goal here is to detect soil layers, you want to find a spot that is reasonably close to the surface, this
is your back not mine,and if necessary scrape a flat vertical surface on one side of your hole if you are truly digging in undisturbed Earth a little dressing of the
sides of the hole will clearly show layers or bands of earth, exactly as It was laid out eons ago, If you don't clearly see bands in the soil then the most likely
answer is that you have disturbed earth. Hopefully you have a wide band of undisturbed Clay .

Our final goal here is to find a nice thick band of Clay that after you carefully remove the 'overburden' you will have a nice clean table top that you can then
carefully remove to a separate tarp, being careful with these steps improves the final product and cuts way down on your further handling !

I just re-read the entire Thread, and remember reading that you wanted to use the Clay / soil from the crawl space of your basement, so I guess you will need to
modify things a little, if you have to work on your knees with a couple of work lights to mine for a slightly less silty Clay Sand mix, you certainly will feel like a
archaeologist ! Basically, i am kinda winging it here as I have been blessed with beautiful Blue Clay that has great characteristics !

If you start out with a ball of the best clay you have now, about the size of a medium egg very wet, flatten it out in the palm of your hand and patty cake it until
it has a shinny surface from the water escaping then watch carefully as you open and close your hand, lots of good Clay will remain shinny, to much silt and the
lump will become dull as the water is reabsorbed !

Worse case scenario, you may need to contact an excavation contractor- tell him you just need a little clean fill for a very small job and you can come and get it.

I expect that you can use the clay you have to make cob, But every where you need to use a Clay slip The best that you can come up with is what you need,
outside of that saving your best Clay for the Structural cob And your finish coat, you probably will still be ok, I Think Big AL

Well, I can tell you this about my clay:

When I work it over with a trowel, I am able to pull moisture out of it, then let it dry a bit, and repeat, just like finishing concrete. About the best that it gets once dry after troweling is very smooth, but no sheen at all. I had assumed that a good sand\clay mix would dry this way.. but maybe I should be seeing a good sheen on it once all dry?

And thanks for the help!

Also, could my clay simply be in need of a lime wash once finished to hold its surface in tact from normal wear? (Never tried lime wash)