Long time lurker, first time poster in need of assistance: Dome House

Hello everyone!  I have read so much in these forums and learned so much from all of you.  I became interested in RMHs several years ago, and I'm now finally getting around to doing it for reals!!!  I'll give you a super short summary to catch you up, then ask my questions.  I first learned about RMH about 10ish years ago while I was living in Gilbert AZ. My wife and I always wanted to move back "to the country" somewhere and we finally did, about 4 years ago we moved to Snowflake AZ where we have been attempting to homestead on our 26 acres.  We bought the 26 acres and have since installed a well, septic, and most importantly, we built a geodesic dome house.  We have been living in the house for about 1 year and we have our "certificate of occupancy" and all of that other fun permitting stuff is now complete.  I bought a Liberator gen2 rocket stove...probably 3 years ago now and it has been my plan for creating a RMH heater in this house.  Now the fun begins... The original plans were not followed exactly, and the place that was previously dedicated for a wood stove is no longer a good option (see drawings below).

1. The place originally designed for a wood stove does not have a clear/straight shot up and out for a chimney any longer.  An on-the-fly adjustment to the upstairs bathroom layout/wall layout made building the upstairs bathroom much easier, but eliminated the "void" that should have had the chimney in it.

2. I had previously decided to install the stove as indicated in the 2nd drawing as I want a bench along that wall.  It is a great place to sit to take off/put on shoes.  It is open above and will allow for heat to rise up and circulate through the house better than many other places.  (I finally moved the stove into the house and when looking at it there... I came up with what I hope is a better plan).  Note, I would have to run the exhaust of the stove through a wall... which I don't love the idea of...

3. I've re-watched a whole bunch of videos and have decided that I would like to utilize the "bell" design vs the duct design in designing the mass storage of this RMH.  Specifically, we like the way WalkerStoves has done and explained bell systems.  So, as my wife and I were discussing where/how to install this stove last night, we came up with what we thought might be a winning design.  It is complicated to explain so see picture 3 below.  This is where I have the most questions.  1, does the shape of the bell/mass storage matter?  Can we make it in this odd shape to accommodate out desired outcome?  Would it be better to "block off" the portion to the left of the stove? Would it make any difference?  It this option, I would not run the exhaust through the wall, rather around it in bench format.

4.  I am open to other ideas... any of you who can/want to suggest a different location or setup, feel free!  Thank you all very much!!!

(special thanks to WalkerStoves, Uncle Mud, and the FCH video we purchased on Permies with hours of great info)

Some things that cannot be changed.  We have the Liberator stove, and don't want to change/build/use anything different.  We paid for it, we have it, and we want to use it.  Dome house floorplan... we built it and are living in it and major changes just aren't going to happen.

Also, I should mention that we currently heat the house with a radiantly heated floor that uses an on-demand propane heater, which is the same heater that heats all the water in the house.  We lived in our house last winter, and the radiantly heated floor worked so much better than I anticipated... it was lovely.  THE ENTIRE house was heated evenly and wonderfully... we just used a bit more propane than expected.  I strongly believe in having at least 2 heat sources and have always planned on using this Liberator in the home, but it will take a bunch of experimenting to find out the best way to heat the home .  The dome is very energy efficient and has surprised us in more ways than one on how much we like it!!!...as well as a few things we would have done differently if we would have thought about it before building it, but such is true with almost anything right?!?

Here are some real pictures with the stove positioned with the "straight through the wall" location and the "lets build an odd shaped bell/bench around the wall location"  

the bench would go along the wall were the saddle and junk currently is

let me know if you have any questions!!!

I would vote for the longer bench/bell. I think having bell closer to the center will help heat more evenly, and you probably need more length of seat-height and width bell to use the potential of the Liberator. I have heard that there is information about the size of bench that the Liberator can handle; you will need to find that, presumably from the makers, before finalizing bench plans.

As for dimensions, the wider the space, the easier flow will be, and I would probably not make any part of the bell cavity less than a foot wide and about 10" to a foot high. A small extension opposite the ultimate flow direction will work as long as it is open to the rest, with the same ceiling height.

Masonry heater code calls for a 4" clearance from the mass to combustible walls, and I would not give less than 2" even if you don't need to follow code. The wall stub with wood post at its end is difficult. You would want plenty of flow space to jog around it. I would really want to cut out the wall at bench height so flow can go straight through, but the post is an issue. Would it be possible to cut the post 6" or a foot above bench height and support the base with masonry?

Aethetically I much prefer the second option with the longer bench. The symmetry against the wall behind in the central area is more pleasing.
I suspect that the bench behind the stove itself will not be very useful for sitting on until the stove is off, as the stove will probably give off too much heat....?
Presumably the flue will exit the far end of the bench in the entry area.
You have a lovely home, thank you for sharing with us.

Why locate the stove next to the kitchen?  Why not across from the other wood stove?  Making heat sources more reliable?

The original wood stove location became infeasible due to upper floor changes, so the Liberator will be the only stove.

Hello all!!!  Thanks for the replies!!!

1. The 4x6 exposed wood that you see is NOT load bearing and I have been planning on cutting that so the bench can go through that space.
2. I'm planning on placing a metal heat shield along the wall on standoff spacers before building any of the masonry, so that should help too, along with a gap between heat shield and bench.
3. The rest of that small wall is load bearing and I've not yet checked to see where the studs are... I know that there is a jack stud and a king stud right next to the exposed 4x6 that cannot be cut, but between them and the next wall may all be open space.  I'm not sure that is helpful for the "wrap around" bench idea, but in theory, if I did the "straight through the wall" method perhaps I could super insulate the stove exhaust through the wall... not my favorite idea any longer... aesthetically the stove looks better centered on the larger wall and the wrap around bench would look much better too.

4. As mentioned, the original floorplan stove location is a no go as directly above it is the "hallway" that goes around the 2nd floor and the original plans had a hollow space for the chimney but mid build I wanted to utilize straight and uncomplicated walls upstairs, so my closets and walls do not match the upstairs walls as per the plans.  Up stairs bathroom door is now along the hallway and the shower is more or less right where the chimney would have gone.

5. Why next to the kitchen?  Well, if you look at the plans, the area where I'm planning to use the stove... the area by the front door, is all "open above", which makes it super easy to run the chimney up and out.  (side note, I'll post pictures of the kitchen, but I have a massive industrial style cook stove that I love, but found out that running all the pilot lights (7 total) uses a lot of propane.  As such, I have a shutoff valve that is easy access and the stove stays off unless in use.  During the winter last year, we left them all on, and the heat from the pilots adds up, but we think that may have been a bigger contributor to propane use than we originally imagined.  During the summer, the extra heat is NOT welcome, so we moved the shut off valve to be easier accessed.  So, we now only turn on the propane when we are going to cook, then turn it off.  Summary:  kitchen does not generate much heat for the house)

If anyone wants more pictures of the house, I can provide, just let me know.  My wife and I built pretty much the whole thing by ourselves.  We did get some help here and there from friends and neighbors and we paid for the concrete foundation and the siding.... other than that, we did the rest of it ourselves.

Here is another question back to the group:  How can I determine the size of bench the Liberator can handle?  I do have the instruction manual that does discuss a mass bench, but it mostly talks about flue run and maximum length flue.  That said, I know Uncle Mud did a half barrel/flue mass bench that was 16ft long and used the liberator for and that was well beyond Liberator's suggested maximum length.

As for bench height/width, I was planning on seat height of 20-22" and width along the long wall of approx 24".  The height would be the same in the area behind the stove, but would be as narrow as possible, I was planning on an interrior channel width not less than 6" so to remain bigger than the 6" exhaust out of the stove.  I was hoping to be able to keep that narrower width around the corner (again, the exposed 4x6 would be cut out of the way of the bench) and then open up into the bench.  As a side note, from the long wall the bench would be on to the current edge of the 4x6 is 24", which is my ideal bench width.

Thanks again everyone!!!

So you potentially have 24" - 4" - 3" = 17" clear between loadbearing studs and back wall. Allowing 3" clear (1" behind shield, 2" in front), you get 11" max for flow channel plus sides. I would make the sides in that spot from a couple layers of cement board so you have 9" clear width inside, which I think would be adequate, and keep the 4x6 and run the face of the bench flush with that. (All assuming you find you can clear the area of other framing.) I think that would look much cleaner than trying to snake a too-narrow bench in front of the post.

Close!  I just verified with a stud finder.  Going from right to left, the space is as follows:

4x6 (not load bearing)
Jack stud 2x4
King stud 2x4
Empty space
2x4 stud

distance between studs is 16" centers which makes the gap 14.5"

so, following your math 14.5" - 4" - 3" = 7.5"  (not exactly sure what the 4" represents nor the 3", so if you could elaborate on that, it would help me  but I don't think we could take too much more away from that.  Let me know what you think there.  I've added a picture since I find visuals much easier to wrap my brain around.

I should have added... I like the concept of going through the wall best, but making it work and making it work safely is my top priority there.  I could empty the entire space between the studs and utilize highly insulative materials (fire brick? ceramic fiber blanket? other ideas?) to make the "channel" through the wall, but also want to ensure there is plenty of "flow" space for exhaust gasses.

4" is the 4x6 and 3" is the jack + king stud, so you can disregard that.

If the stud next to the long wall abuts studs in the long wall, you could lag that stud securely to the long wall in several places and cut off the base of it. The other studs will be plenty strong enough to carry the load to the floor.

Cement board (Durock type, not Hardibacker type) will be fireproof and durable enough while being thin yet continuous. Rockwool would be extremely heat resistant, you don't need the expensive refractory insulation for that location. There is rigid rockwool insulation board though I have not personally seen it, and a layer of that plus a layer of cement board on the inner face would give insulation plus containment.

Yes, I could lag the far left stud and gain that 1.5" there is a lot of other load bearing support in that area and with some lags would be of no concern.

If you could provide an ideal material cross section / channel drawing idea, that would be super helpful!!! I want to start lay out with painters tape and see the beginnings of what will be and begin a materials calculation and list.

Ideally I would have this built and operational before December... it's not cold yet, but will be getting there sooner than later!!!

Kendal,

I was just wondering if you were considering placing a prefabricated chimney in the original (bathroom wall) spot? Bathroom is the place that in my opinion should be the warmest. On the other hand the pantry should stay cool and your chosen location will add heat there and will be also far off the center of the building.

There is a potential way to use the original location but it would be to use a more vertical mass bell, not a bench. It would also require going and venting out the side wall of the house and then up.  There is a lower ceiling in the Master bathroom to allow for plumbing without going through floor joists.  There is no vertical path out from that location. Summary: while possible it would be challenging and may be more difficult to get proper draw and would not provide a bench to warm our buns on

While I agree regarding pantry temperature, as is, the radiant floor heat also heats the pantry, so it can't be helped too much. Also, we have other storage for long term food stores that is cool and dry. Our pantry is more for frequently used and quickly rotated foods, and along that particular wall it is mostly food appliances, trash bags, paper towels, empty jars and other non-food items. Food items are on the far wall closest to the kitchen. Also, at least right now, the pocket door is not installed.

Lastly, I get comments about central location.  The original stove location is the same as the proposed location however it has the added benefit of the mass storage being in the "open to above" location to get the heat up to the 2nd story better.

I'm trying to picture what your interior ceiling looks like that it would be difficult to run some 6-8" HVAC ducting up and out of or near the center of the dome...

Coydon Wallham wrote:I'm trying to picture what your interior ceiling looks like that it would be difficult to run some 6-8" HVAC ducting up and out of or near the center of the dome...

The area directly above the original stove location on the floor plans

The ladder is our current method of opening and closing cupola windows...eventually we will suspend a loft floor up there so we can enjoy the view from up there.

I'm happy to post more pictures or even videos if anyone wants them. I'm very happy with our dome home that my wife and I built almost entirely by ourselves!

No doubt a central stove with a chimney exiting dead centre would be not only very efficient but also very cool (excuse the pun)  
The required chimney pipe could just be cheap thin wall for the majority of the upper length and could be painted a nice colour.
The pipe would be hung and supported from the roof end.

Fox James wrote:No doubt a central stove with a chimney exiting dead centre would be not only very efficient but also very cool (excuse the pun)  
The required chimney pipe could just be cheap thin wall for the majority of the upper length and could be painted a nice colour.
The pipe would be hung and supported from the roof end.

Yes to all accounts!!!

However, it would also take up real estate in the large open living room, and once the loft is installed we plan on putting a large fan on the bottom of it to help circulate the air in the whole house. Both of those prevent a chimney in the center. Great idea though, and we have considered it.

Yes I can see that having something in the centre of your living space could be a negative.
With the development of riser less stoves with powerful chimneys, you can can now have a low hight stove that can actually look very appealing and serve multiple functions like an oven a hot plate, instant radiant heat  and a mass heater.
In the past most rocket stoves had an ugly barrel and an unappealing high profile that would not be at all attractive in your lovely home.
So it might be possible to build a lovely central multi  purpose feature rather than just taking up room.

However I must point out that at least in my end of the world, modern metal box stoves are also super efficient, low wood consumption, insulated and produce very low emissions.
They are not mass heaters per.say but very attractive to look at.
Sorry I know I have deviated from your ordinal question!

Your input is appreciated. Had i had the knowledge when this house was in design phase that I have now... things would be different.

Alas i am now in the position I am and design constraints are what they are.

I think I'm sold on the new location and a bell bench that ends along the entry wall. Going through the wall seems doable I just need to finalize design and materials especially for that area.

No need to have the RMH in the middle of the footprint with the pipe running straight up and out through the center of the dome top:
Also, with the bench as a stratification chamber, the exhaust can be right next to the Liberator on the central side of the bench.

Coydon Wallham wrote:No need to have the RMH in the middle of the footprint with the pipe running straight up and out through the center of the dome top:
Also, with the bench as a stratification chamber, the exhaust can be right next to the Liberator on the central side of the bench.

I'm still debating where to place the exhaust. With any luck I'll start a layout using tape tonight. This will help my visual brain see things better. Also another chance for feedback from the experts here before I start buying materials.

Your picture showing exhaust going up at an angle gives some extra ideas, but the very central part of the dome will not be an option, but any point up to where the loft will eventually go is available. We will see how it all comes together in the next several weeks... or as long as it takes!!!

Kendal Webster wrote:I'm still debating where to place the exhaust. With any luck I'll start a layout using tape tonight. This will help my visual brain see things better. Also another chance for feedback from the experts here before I start buying materials.

Your picture showing exhaust going up at an angle gives some extra ideas, but the very central part of the dome will not be an option, but any point up to where the loft will eventually go is available. We will see how it all comes together in the next several weeks... or as long as it takes!!!

Discussions I've seen on RMHs with side wall exits have been about irreconcilable problems, sounds like it is always more rewarding to put time in figuring out how to have exhaust exit through the roof (or highest point available). More efficient in radiating heat from the exiting gas into the building, and avoiding problems with airflow around the building. Looks like plenty of room in the triangle frames adjacent to the cupola, the closer to the peak the better...

My 2 current choices are:

1. At the end of the mass bench, closest to the front door. In this location, even if i go straight up, puts the top of the chimney somewhere around 15-18 ft up. I could angle back towards the top of the dome.

2. Near the wall on the entry side. A straight shot up from here is very near the top height of the dome so the extra length outside would be close to the total height of the dome.

Which brings up a question I've had.  Can the chimney be too tall? It seems like a very long way for cooler (compared to standard stove) exhaust to go. Is there concern for wrong way flows from that extra height?

There probably is a chimney length that is too much, but probably not within reasonable actual conditions. Since a properly functioning RMH will have no creosote in the exhaust, the only real need is to have the exhaust warm enough to rise through the chimney. If it is noticeably warmer inside than out, that handles itself. In shoulder seasons where the house is cold but the air happens to be warm outside, a tall chimney might be a problem.

I definitely suggest angling the exhaust as needed to exit high in the dome, wherever the best arrangement is for all functional considerations.

I'll temper my previous statement by saying that shapes like yurts and domes don't suffer much of the problems with wind as more blocky buildings do so that might not be a large concern in your case, but there would still be clear benefits to having the exhaust exit as high as possible.

I've never heard of a chimney that was too tall that it worked negatively against draft...

Here are 2 pictures that correspond to my 2 options.  The first picture is directly above the end of the bench where I could easily use a "T" for a clean out/ inspection / chimney primer if needed. It hits the ceiling at 17'4".

The 2nd location is close to the wall that we will be going through. It would need to go through the top of the bench, and would take up some nice sitting area. It hits the ceiling directly above at 24'1".

Personally I prefer the 1st option provided would get sufficient draw. Yes, I could still exit in the first option and angle to the 2nd location but I would prefer a straight shot for ease of construction/ install/maintenance.

Other pictures are added so you can see perspective if you follow the patterns you will know locations. You can sort of see the "bridge" that is in the area above the entryway/living room  division. You can only see the higher location from the perspective of viewing the stove.

My lovely wife was kind enough to help get this picture showing both locations while I was upstairs too. It helps give perspective.

With nearly 7' of difference in height between the two options, I would greatly favor the higher exit point. Even if you don't end up quite as high with the termination from the lower point, you would have a free stack exposure large enough that bracing is probably needed, which adds complexity and potential leak locations.

List of questions.  Toying with 3 completely separate answers so don't think this is related.

1.  What is in the triangle behind the fridge in the first floor?
2.  Does the under stairs closet contain anything essential?
3.  Where does the in floor heating lines come up?  Tank for that? pump for that?
4.  What if the rocket mass heater changed from a bench to a zig zag wall mass and moved next to the stairs?

C. Letellier wrote:List of questions.  Toying with 3 completely separate answers so don't think this is related.

1.  What is in the triangle behind the fridge in the first floor?
2.  Does the under stairs closet contain anything essential?
3.  Where does the in floor heating lines come up?  Tank for that? pump for that?
4.  What if the rocket mass heater changed from a bench to a zig zag wall mass and moved next to the stairs?

Great questions!

1. The triangle shaped room behind the fridge is a pantry. The items stored along the wall where the bench goes is full of non-food items such as extra appliances, empty jars, paper towels, trash bags, etc.
2. Under stairs storage currently contains: brooms, mops, tools that get used frequently, leftover paint and supplies, and is also where the electrical/breaker box is located.
3. All of the in floor heating stuff is in the laundry room. It is a tank less system and utilizes the same on demand heater as the rest of the house. Pretty cool design. I ordered the kit online and received great support throughout install.
4. Next to the stairs is currently the music room. The piano is along the longer wall. Bass and cello and music stands are along the shorter wall.  So...yes, we could change to a zigzag on that wall but I don't like the idea of the stove on the same wall as all the electrical home runs to the panel, and that place is perfect for the piano and the rest of the instruments fit well there too. Lastly, regardless of if it is a mass bench, I've wanted s bench along the other wall since construction began as it is a perfect place to take off/put on shoes and coats and the like. Double purpose makes it even better!

Also, I know heating the pantry is not ideal. We will have a larger and better temperature controlled food storage outside within a year or two. The inside pantry contains frequently used stuffs that really aren't affected by some heat AND without the stove, it is already heated by the i  floor heating...I wish I would have thought about not running the pipe through there, but it also would have been very difficult to  skip based on the plans given us by the kit... simply said, there are several runs that make big loops and skipping that space would have made the loops a lot more difficult. Not impossible, but considering we laid the PEX pipe in December, it was not the most pliant and flexible.

OK, now for a little info on the floor heating,  just for fun.

1. It works WAY better than I imagined it would.
2. It works way differently than I expected.
3. The ENTIRE house is heated comfortably and evenly with a slightly higher temperature on the 2nd story. (Hoping a large fan under the loft that will eventually be built for the cupola will help with that and with cooling in the summer. )

I expected that the floor would be warm and walking barefoot or in socks would be nice... warm feet, warm body. I expected that the air temperature would not have been affected nearly as much, so warm toes and cooler air temps.

What actually happens is that the air temperature is affected greatly and the floor is warmer than it would be, but still feels cool to the feet. The temp controls can be adjusted to work off floor temperature or air temperature or both. It didn't seem to make a lot of difference between floor control and air control. My wife had it set at 70 (yes a few degrees cooler probably woul save some cash on propane but she is a bit cold-blooded so happy wife happy life!). Anyway, the whole hose stayed at 70 all day and all night and there was basically no hot or cold spots in the entire house. It was very comfortable (if on the warm side) everywhere.

The little closed triangle behind the frig? (potential stove pipe location first floor)  Not the room.(more later don't have time now.)

C. Letellier wrote:The little closed triangle behind the frig? (potential stove pipe location first floor)  Not the room.(more later don't have time now.)

Doesn't exist. House not built 100% to plans. We hate "dead space" so it is part of the pantry area.

Well, my wife and I started laying out the bench area with tape on the floor and long story short, we decided the Liberator will live in front of the short wall and exhaust will go straight through it until the bench. All in a straight line.

Here is why:

1. Aesthetically we liked the stove centered on the larger wall, more or less centered in that space. It seemed to "fit" better there and looked "right". Since we determined that a bench could go behind there and wrap around to the long wall, we thought this was going to work out well. HOWEVER in practice this took up a lot more space and became an obstacle when walking out of the kitchen. When looking at laying out the "hearth" area... it was huge and encroaching a lot into the living room space and "flow". We put the Liberator on a furniture dolly so that we can move it quickly and easily and when we put it back in my original location of in front of the short wall, we immediately observed that it took up a lot less space and felt way less invasive and was way less of an obstacle walking out of the kitchen or the entry way.

2. We talked about putting something to the left of the stove to "balance it out" and moved a plant shelf tower thing there and wow! That works! Yes,yes, I know plants won't survive there when the stove is running, but for the other 9 months, it looks lovely. During the 3 months of use, perhaps wood/pellet storage bin, some stacked bricks for more thermal mass, or something else could go there to "balance " the space.

3. It would use a lot less material. Even just the hearth will require less than half the bricks. The bench becomes one basic rectangle with a lot less bricks and way less funky angles and such. Let me be clear here...we are on a bit of a budget and saving as much as possible is very desirable,  but we would have made it work the other way if we really felt it was best. However based on point 1 and 2... it really is better in our minds.

4. Due to the limitations of the Liberator, I think the roughly 9 or 9.5 ft bench is about the most mass that stove will be able to utilize effectively. I believe the manual suggested a flue bench of 10 ft max. I have no experience in calculating stove output vs optimal mass storage and wouldn't even know where to begin. That said, I know Uncle Mud made a bench of half barrels utilizing a flue and cob for a 16 ft run and that worked, in fact I really liked how that looked and considered doing a build similar to that, but my wife and I ultimately decided a bell seems more efficient and building with bricks looks "more refined" and just better.

Pictures. Final "we hope " stove location with plants as described above. And bench layout...yes... stuff got moved into the area but you can still see the basic tape outline.

OK, I've had many things come up, life happens, and I'm back to working on this project. I'm trying to make a build plan and budget. I'm a little bit stuck and could use some help.

Mortar. That's what I don't know enough about. What kind do I need? Do I need to use the high heat mortar for the entire bell bench? Only the top 1/3 layers?

Pros and cons between using rock vs bricks? I'm going to compare price of 4"-6" river rocks vs bricks but I think rock will be significantly cheaper and I like the look of rock, but would brick be better? If so, why?

For mortar, building code in the US requires refractory cement (around $50+ for a 50 lb bag of powder) for all heat-exposed and combustion-product-exposed areas. This would not include exterior bell facing stone or brick. Many builders recommend a fine clay-sand mortar (explicitly prohibited by the code) as the best material.

Clay is easy to dismantle and reuse if ever desired and easily cleans off of bricks. It does not cement the masonry together, just beds units firmly.

Refractory cement is strong and permanent, but may destroy the bricks if you ever try to take it apart. You decide which suits your situation better.

The choice between brick or stone or other exterior material is strictly esthetic and practical, though denser materials hold more heat for a volume. The idea of buying stones boggles my mind... of course I do have a large steep creek with unlimited stone bedding, and any digging job turns up a good number of stones.

Glenn Herbert wrote:For mortar, building code in the US requires refractory cement (around $50+ for a 50 lb bag of powder) for all heat-exposed and combustion-product-exposed areas. This would not include exterior bell facing stone or brick. Many builders recommend a fine clay-sand mortar (explicitly prohibited by the code) as the best material.

Clay is easy to dismantle and reuse if ever desired and easily cleans off of bricks. It does not cement the masonry together, just beds units firmly.

Refractory cement is strong and permanent, but may destroy the bricks if you ever try to take it apart. You decide which suits your situation better.

The choice between brick or stone or other exterior material is strictly esthetic and practical, though denser materials hold more heat for a volume. The idea of buying stones boggles my mind... of course I do have a large steep creek with unlimited stone bedding, and any digging job turns up a good number of stones.

Ok, now i have a different question. What material to make the bell bench with? In my mind it was going to be made of brick or rock, just a hollow box with brick or rock walls.  Do I/should I make it differently?

Brick has enough texture that even clay-sand mortar should seal it up in bell walls. Stone that has textured surfaces and shapes that would allow stable dry-stacking can also be reliably clay mortared. Smooth round stones would depend entirely on the clay between them remaining sound and not cracking, and I would never make a single-skin enclosure with them. I would feel good about making an inner skin of a couple inches of cob, being sure to seal up any cracks that develop in drying.

Glenn Herbert wrote:Brick has enough texture that even clay-sand mortar should seal it up in bell walls. Stone that has textured surfaces and shapes that would allow stable dry-stacking can also be reliably clay mortared. Smooth round stones would depend entirely on the clay between them remaining sound and not cracking, and I would never make a single-skin enclosure with them. I would feel good about making an inner skin of a couple inches of cob, being sure to seal up any cracks that develop in drying.

Thank you! This helps a lot!

I'll draw up some plans and post them to see what you think before I start building. I'm also going to see if there is any place I can get enough clay in our soil to make cob. Most of what there is around me is "silty loam" , sand, and "blow dirt". But I have noticed a place or two that may have higher clay content and might even be suitable for cob almost directly... that will be an interesting experiment.
Thank you!