Has anyone worked with codes for RMH in Delaware County NY

Hey! Looking to build my first RMH in Delaware County, NY. Curious if anyone in this region has done the same. Would love to discuss sourcing materials and building codes in the area. Thanks!

Hi Sophie;   Big Welcome to Permies!  And A Big Welcome to the wonderful world of rocket science!

So your planning on building your very first RMH!   That's great !
So tell us your plans?  I assume a J tube build?  What size were you thinking?  6" or 8" ?
Were you planning on a piped mass with bench?
As I'm in Montana I can't tell you exactly where to buy supply's in your area. But tell me what your looking for and I'll point you in the right direction.
As far as building codes, they very state to state and even county to county.  If you are rural in a forested area then that county may have realistic wood burning codes.
Insurance company's are another issue that may be easy or insurmountable depending on circumstances.

Thanks for your reply!
Yep, going to start with a J-Tube although interested in a Batchbox, J Tube seems like a better place to start out. Thinking 8". I have a used 8" double walled chimney in pretty good shape that I'd like to use to cut down on cost, although I know there are some warnings against that. Just hoping I can get it cleaned out really well. I am also thinking about doing a casted core with perlite, fire clay, and chimney cement as I have some experience with molding and feel more comfortable with that method hypothetically. Curious to hear from people who have done a casted core or experimented with both (fire brick and casted core). And I am thinking of doing a cob bench, although we don't have much local clay here. Just feels like a more forgiving medium for a first time builder. The heaters going in an outbuilding with a thick cement floor, but combustible walls. Spending time now also thinking about heat shielding or if I should just plan for placement to be far from any walls at all. Would love to hear your thoughts, thanks so much! Sophie

Hi Sophie;
I hope you are ready... I'm about to bombard you with information!

Yes an 8" J tube is a great place to start. By going with an 8," if at a later time you decide to go with a batchbox.
You can build a 6" batch and plumb it right into your 8" mass. They work very well that way.

So not sure I understand about your double wall chimney pipe?  How were you hoping to use it?
As a final go thru the roof?  Or were you wanting to use it inside your mass?
For going thru your roof it will be great.  If you are wanting to use it in your mass it will not be good at all.
Here's why) A double wall pipe would keep the heat in it. You need that heat to radiate into your cob and rock mass.

To go thru the mass you use one stick of regular stove pipe as you leave the transition area and then you switch to H.V.A.C. pipe. It's WAY cheaper!
Home depot sells 5' lengths for around $11 each.   No need for strong pipe away from the core. Use hvac pipe all thru the mass.
When your pipe comes up vertical out of the mass, you would want to switch and use one stick of regular stove pipe.   From there on up you can use any pipe until you go thru wood, be it your floor or your roof.  When passing thru wood that is when you need double wall.

OK, lets move on to a casted core.  Fireclay and perlite is all you need to make one.   I built one as my first core!   It worked great at first.... but they are so soft that adding wood will wear the feed tube so much that it will not draft properly. I used it one season. Patching the feedtube weekly.  It started out as 7.5 x 7.5"  but by spring it was the size of a five gallon bucket!  
They work but I do not recommend one.

The best thing to use right now is ceramic fiber board.  It will cost more but the insulated board gets your mass hot very fast.
Otherwise if cost is a factor then I recommend that you use firebricks to make your core.  Its easy!
Then, I highly recommend making a five minute riser. Rather than casting a perlite clay riser (I've done that as well and they do hold up)  BUT a five minute riser is fast and outperforms a cast riser every time.

Now lets talk about your Mass.   I highly recommend doing a red clay brick surround, rather than an all cob bench.  This makes your mass build much much easier.   You do not need huge amounts of clay and sand.   You need some local sticky clay but not much. Then you need rocks! The larger the better.  You put 4" of clay and cut straw down on the concrete. Lay your 8" pipes on top of that.
Carefully encase those pipes in plain sandy clay mud. After that add rocks.  Put clay mud around those rocks so there are no air spaces. Keep raising your red brick surround as you bring up the clay and rocks in your mass.
I will enclose old photo's from my first build, as an example.
Next question about your mass.
Were you planning on making a 180 degree turn and coming back towards the core before going vertical?  As that is how the Wisners recommend building,  I suspect that is your plan.  
Here is a much improved idea. Rather than making a 180 turn  (restricts your flow and is a 10' deduction in length)  Build a mini brick box. Run your pipe straight into the box and the other straight out. Add a cleanout lid at that box and you are golden!  No flow restriction and its easy to clean out that far end.

Now lets talk about your combustible walls.   Your mass itself is not going to get hot enough to worry about, usual surface temps on my mass are around 100 F.   But your core and barrel are very hot.
On my build, the mass is along a wall. But I turned the core 90 degrees off. This put the hot barrel plenty far from any wood.  
I did not use a cut barrel as my transition area (something the Wisners recommend) Instead I built a small brick box behind my core and ran my horizontal pipes out from there. I also have a cleanout door there as well.

Well Sophie you asked for my thoughts.... you got them!  
I realize it all sounds confusing.   Its really not.
Just ask for clarification on my ramblings and I'll do a better job of explaining.

 

Wow! First of all, thanks for this reply, it is incredibly helpful.
Some responses and more questions if you dont mind!
1. yes the double walled chimney pipe would just be for going through and out the roof. Thanks for the insight on which pipes to use where that is good to know!
2. I watched this Matt Walker video if the casted core, https://www.youtube.com/watch?v=7ANMXGrxgnE&t=16shttps://www.youtube.com/watch?v=7ANMXGrxgnE&t=16s, I notice the includes fire cement and fiber glass in order to make a stronger core, do you think this could reconcile  problems with the wood wearing the core away? Also curious about a combination of the two methods, maybe using ceramic fibre as the inside of the feed tube? (or inside of the mold entirely?) or would that just be overkill?
3. I haven't heard of the 5 minute riser and wasn't able to find much on google. Are there resources you could point me to?
4. I like the brick idea, but I also really how cob looks. Thinking about a combination between the two? Maybe brick going 1/2 or 3/4 of the way but still having seat be sculpted out of cob?
5. Also interested in brick box idea but having trouble visualizing. Does the brick box maintain that 8" CSA? and is it buried within the base? How would you ensure that exhaust does not escape through the box?
6. And lastly, in the final picture it looks like your barrel is covered in something, and not exposed? Would love to hear your reasoning for doing that?

Thanks so so much for all your help!

Hi Sophie;
Good timing on your response!  I'm waiting on dinner and have time right now to respond!
1) Excellent place for it.
2)Adding things to the cast mix would help overall, but building your feed tube with split firebrick is the long term solution.
Even when you build with ceramic boards you still use split bricks in the feed tube. ( ceramic board is on the soft side.)
3)Well I can and will, but not till I mention that you are at one of the better places to search rocket info. right here at Permies!
here is a link    https://permies.com/t/95849/Working-Morgan-Superwool-ceramic-blanket
4)Well you can build anything that suits your fancy.  Using the brick is fast and add's another layer of mass.
And yes designing a sculpted cob chair could certainly be done.  Read up about final finishes in the cob forum.  https://permies.com/f/76/cob
5) The brick box is a small "bell"  also called a stratification chamber. The 8" pipe leaves my small bell at floor level.   I do not have a second small box at my 180 turn. It was an innovation that  came along with the development of batchbox's.   My J tube was first built in 2013, the only book available was Ianto Evans book  and the other place was here at Permies.
You simply replace the 180 turn with another small bell. The pipes enter and leave down low.  Leave room for ash to collect below the pipes  and have an external cleanout cap to clean the ash.
6) My barrel is covered in cob except for the last third.  It is in an uninsulated  green house/studio that we heat all winter.   We need all the mass we can get.
Dinner is here !

Sophie Gell wrote:
5. Also interested in brick box idea but having trouble visualizing. Does the brick box maintain that 8" CSA? and is it buried within the base? How would you ensure that exhaust does not escape through the box?

Hi Sophie,    One video that shows what this looks like and then modified into a large bell by Kirk 'Donkey' Mobert is here: Rocket Bell Retrofit
With each innovation came new ways of looking at how these heaters are built. One technique not necessarily being better than another but certainly offering a choice based on a persons skill level, materials on hand and goals.

I appreciate your enthusiasm and look forward to observing and helping out if I can with your progress.

For a cast core, refractory cement is a good material. It is expensive (around $50 for a sack if I recall correctly), but will stand up to wear. I would still line the feed tube with split firebricks. It is easy to make an internal form the exact shape you want your cavity from scrap wood and plywood, allowing a path for air to move through the inside of the form, and then burn out the form with the first firing.

I am in Broome County, and did not involve the building code inspector in my project, though I expect he would not have had an issue with it. My town is one where many ordinary building permit applications are made in sketches on a sheet of paper. It depends on how strict your local officials are and how much fuss they would make.

Thanks everyone for your responses. So now I am thinking about a firebrick core possibly with a 5-minute riser. I had some questions about the riser. Do you need to use stove pipe for the riser? For an 8' system could i still use 8" ID pipe with the 1" that is subtracted from the area by the superwool? And in terms of the connection of the riser to the core, would you just sit it on top the opening from the burn tunnel and seal around with clay sand?

Thanks!

Hi Sophie;  
Yes, you use stove pipe or sheet metal.    
You need a 10" circle to make an 8" riser.   Make your own with rivets or sheet metal screws.

Yes, the riser sits on top and clay / sand mud seals it

Thanks everyone for all of your help!
After trying to do some material sourcing over here it looks like ceramic fibre board is actually gonna be cheaper than the insulating fire bricks! So I think i will go with the fibre board core and 5 minute riser. Searching around I'm seeing a lot more fibre board Batch boxes than J-Tubes. Do people have success with a fibre board J tube? I saw one thread where a guy's core melted through 9https://permies.com/t/96634/Build)  but he had some other stuff going wrong, and another where the decided to build the core only partially out of the board (https://permies.com/t/92302/Ceramic-blanket-riser-board-core). I am planning to do the walker plans, with the feed tube lined with splits but ceramic board throughout otherwise, just want to make sure I'm on the right track. Seems like 1" 2300* should suffice although 2" 2600* might be worth it if there isnt a huge price difference?

Thanks again to all, you are amazing.

Hi Sophie;   Yes  a ceramic board J tube using Matt's plans will rock!  You will be very pleased!
Your seeing more batchbox builds because that is the direction super high efficient stoves are headed.
The J tube stoves will be here forever as a highly efficient mass heater.
They can be built by just about anyone with less than optimal building materials.

For your build I would use 1" on the walls but 2" on the burn tunnel roof .

Oh! Also, ive done some research on stratification chambers and I'm very interested in building it that way I can figure out what that looks like. Can i still do a cob/brick bench? Anyway, will continue the research but any advice on that end is also much appreciated!

Hi Sophie;    Check out this post out about my shop heater.   https://permies.com/t/94980/Brick-Bell-Shop-Heater
It started life as an 8" J tube into a brick bell.
It is now a 7" batchbox

Hello!
I have now done a lot of thread-reading, some drawing and some thinking. I am planning to do a half barrel bell system along w my 8” J, and I have a few questions.

In the space that I was planning to build the heater, I only have room for a 6’ bench. I’ve read that bells are a lot more flexible in size and shape so I am hoping this is alright, but I’m also now wondering if an 8” system is overkill.

Second, I am hoping to set the barrels on at least a 1’ tall brick wall on every side. This will increase the internal area but also raise the seat to the right height as the half barrel are only about 1’ tall at the highest point. Does this sound reasonable? I want to leave room for cob build up on top bringing the bench to about 25” tall, but am. I am unsure of  how thick to make that layer. For the inside of the bell should I line the concrete floor with cob? Or bricks?

Then some quick questions:
1. Do the barrels that form the bell need to have the paint removed? I’ve seen some painted and others who burned it off. Just wondering.

2. Can the pipe that forms the the transition area be cobbed over? On some builds I see it just out in the open.

3. For a bell system does the exhaust inside the home remain uninsulated? As in a regular ducted bench. Then becoming double walled going through the roof and out?

Thanks again you all are amazing.

Hi Sophie;
Great choice and Great questions, lets give you some answers!
To start, a 6" system would probably work, but you will be much happier with an 8".
6" J 's need feeding  a lot more often than an 8".  
You can always enlarge a bell up later, if you feel like your sending to much heat up the chimney.
Setting the 1/2 barrels on a 1' brick ledge will work great.
For your floor in the bell, I would give it a few inches of cob with cut straw as an insulator. You want that heat rising.
Myself, I would remove the paint but I think it would be fine if you leave it.
Yes, cob cover the transition .
As far as how much cob on the barrels, more is better. To thin and your bottom might get warmer than you like!
Yes, a bell works the same as piped mass. Uninsulated pipe indoors and double wall thru the roof and outdoors.

Been awhile since I've been on but I'm I the process of doing some repairs to my heater after a 8 month heating with it. I used fire brick in my feed tube and riser. I'm glad I did because it really gets beat up from the fire wood at the feed tube. So it's a easy repair since I have extra split bricks. If you are looking for clay, I bought some from a local compost company. They use clay in the compost mix, so they may be willing to sell a tractor bucket full. I found fire brick and ceramic wool at a fire place dealer. They carry some for their repairs. I was lucky with the ceramic wool since the Phillips energy store carried it for the local maple syrup makers. Hope this helps!

Hi Folks!
Checking back in! Right now I am in removal process and I am struggling (*i think*). I build a pocket rocket lid and have been burning the barrels with the clay-Mache. Here's what im left with,

I had grinded the paint off the outside of the barrel with the orange residue, and was making trying to burn the paint off the inside with the pocket rocket. Now it almost looks like the clay-mache fired too it and caused rust? I'm not sure, any ideas?

Hi Sophie;
Those barrels will be ok.
The one barrel will be split and used in your bench, so it will be covered with cob.
Any paint residue left on the barrel you use over your riser will quickly go away when you light off your stove the first time.
Another option would be to burn woody debris (burn barrel) in the one to finish getting any paint off.

Thanks for your last response, that is a relief. I have finally gathered most of what I will need and am starting the build this week! Very excited. I have a couple questions first!

I know that the ceramic board riser doesn’t need additional insulation, I am thinking though about setting it on a clay/perlite pad. How does this sound? Setting it directly on the concrete just doesn’t sound quite right. Also the floor is not level in parts, so I was thinking I can level the perlite pad so I am starting from a good surface.

I read on here that bells don’t necessarily need clean outs, however seems like a good idea to add one for good measure. Does it matter how far along the bench the clean out is? And does the clean hot need to be of a certain size or just big enough to get my arm through? I will have two additional clean outs, one in the manifold, and the barrel w a removable lid. Does this sound sufficient?

I am still figuring out what the height difference should be between the transition and the exhaust. I had thought that it was very important that the transition be slightly higher and the exhaust as low to the ground as possible. But In the sundog video he has both down low. Curious about your thoughts on this.

Also, in the Hokkaido build thread, the OP extended the chimney exhaust to the end of the bench to encourage the gases to run through. Because my bench is smaller with no elbow, do you suspect this is not necessary?

I also have been reading about the “plunger tube” that some people use with bells to control draft. Is this recommended or something that can be installed later?

Thank you so much! I’m very excited to begin the build and will be sure to update with pictures.

Hi Sophie;
Sorry for the delay in responding.
Let me take a shot at your questions.
1) Setting your riser on a clay perlite base is a good plan.
2) I would put a cleanout at the far end. Big enough for your arm and a vacuum hose.
3)Both can be down low. The heat from the transition will quickly rise to the top of the bell. Cooler air will sink and find the outlet.
4) With a smaller bench  I think you can place the chimney where it is most convenient.
5) A plunger tube helps with large benches to get them drafting.  With your small bench you should not need to use one.

Thanks so much Thomas!

With a bell system, do the transition and exhaust to and from the bench need to be in line with the 8" CSA of the rest of the system?

Hi Sophie;
The transition to the bell should be as large as possible , bigger is better.
The outlet pipe should be 8" all the way outdoors.

Thank you again Thomas and all who have helped! I'm still only at the beginning :0

I wanted to give some updates!

I have started dry building the brick and barrel bell and laying out things in the room.

Because the bench is in such an awkward place, I am thinking that once the heater is all cobbed and done I would like to build a bed platform coming off of the bench (I.e. not tied into the bell system but visually one form). I am hoping to do this with a wooden platform covered in a thick cob layer bringing it to the same level as the top of the bench. Ideally, with some storage underneath. Has anyone worked cob over wood? I assuming the cob will protect it from any heat danger but not too sure.

Meanwhile I have burned out and cut the barrels, built and did a test fire in the core! I scored a ton of free clay, dug out from someone's pond in Cooperstown, and have acquired some straw bales and a big ole pile of sand.

...then I realized I made a really stupid mistake. I have five 2' lengths of lightly used insulated chimney pipe. All this time I assumed they were 8 inch (thinking back not sure why I assumed that). Well guess what, they are 6 inch. So rather then purchasing 4 lengths of 8 inch pipe (for $200+ a piece!) I think I will cut down my ceramic fiber board core to a 6 inch design. Kind of a bummer as I was excited for the power of an 8 inch but this seems like the only doable course of action.

I think I will be going with a barrel manifold but not sure yet.

Once again all the help has been amazing! I will continue to post the build as I have learned so much from going through other's build threads.

Hi Sophie,   Very nice progress and layout your got.

I have worked with some cob over wood but always just considered it to be a form to hold the cob in place until it dried. After that, the form could be either left in place, removed or burned out if being used to make a core. As far as whether it will be OK with the heat, that really depends on how close it gets to the heat and how much cob is on it. Wood may be alright for a while, but as it dries out over time, its combustion point decreases and charring or even combustion could occur. You could put some insulation between the two materials which would help but if you can build the form to be removable, I would say that would be the safest bet.

Its too bad your chimney pipes were not larger. A smaller front end (the core) and a larger back end (the exhaust pipe) actually works in your favour increasing the draft, but the other way not so much. I'm assuming this insulated pipe you have is going to be used to exit the building and extend outside to your chimney cap.

You may want to consider putting a small wall or divider of some sort between your bed and the barrel for protection.

What is the little pipe at the end of the barrel bench. A cleanout? If so, I don't think it will do much good at the angle its at. Your T at the base of the manifold should work just fine to catch the full length of the chamber. Not much ash would accumulate this far down anyways to worry about.

Gerry, thanks!
Getting there..

Today I did some cob tests with some clay that I have: Hawthorne #50 fire clay, some pottery scraps, and natural clay from Cooperstown. The Cooperstown brick dried up to be remarkably strong, almost waxy, while the other are quite crumbly. Very interesting! Some bricks may have had more water than other so will have to re-test.. I should also say my sand is rather course!

Thanks for your advice on the cob platform. Seems like if I removed the wood frame the cob wouldn’t be able to support much weight. Perhaps I’ll end up doing a solid form or using brick and cement board for the inner form. We shall see! A divider sounds like a good idea! Once the heater is up and running I’ll have an understanding of how hot the bench will get, that will be important information! 

Yess it is a shame about the insulated pipe. It’s a small room so a smaller system isn’t the worst thing. I cut down the core to a 6 inch today. Ceramic fibre board is not as fun to cut once it's been fired :/. Kicking myself now for the amount of board I purchased and wasted as a result of this mistake .

Yes! The pipe at the end is supposed to be a clean out. If it were running vertically into the bench would that be better? I have read that there’s not much ash to collect at the end of the bench but also that it’s worth adding access there if you can just cause. Do you suggest that I’ll be fine with just the removable lid on the barrel and the T at the base of the chimney as clean outs? 

Curious if I can scale my riser down to 6" but keep height (meaning keeping it at 31" rather that scaling down to 24")? I know the riser height should be twice the burn tunnel length but can it be longer? Any benefit to that?

Many thanks as always!

Some excellent test results on the brick samples you made Sophie. This is a huge thing to get right otherwise a whole build can be ruined by a poor mix.
Every location is different so materials need to be adjusted to accommodate proportions. Keep it up until you find what works the best.
Try sifting some of your sand through a mesh if its too coarse. I find that too many large grains can make a batch crumbly.

Didn't know that cf board was harder to cut once fired. Thanks for sharing that.

As far as the end clean-out, do what you feel is best. It would be easy to fill in later but much harder to make one if left out. There's no right or wrong answer here but I would say that if it can be positioned to access more of the bench the better. Perhaps a bit bigger too to get an arm in there if needed.

Just as long as you maintain a proper top gap (distance from the top of the heat riser to the bottom of the barrel) you should be fine.

Sophie;  What tool did you use to cut your cf board?  
I use a hacksaw blade, just held in my hand and it cut's easy straight and clean.
Did not matter if it was new or used.

Thomas- I used a hack saw when I first cut the board, it was quick but left the edges kind of fluffy. This time around I used a box cutter with a long blade to cut cleanly through, though I noticed the singed bits were really popcorn-y. Those parts more inclined to pull off in small chucks then to be cut through.

Gerry- I’ll give it a go today with the bigger particles screened out.

I mixed clay slip into the sand so there was a lot of water. Curious how thick people mix their slip- are we talking smoothie, soft serve, or ice cream type thickness?

And thankfully, I have a very small arm! Made sure I could slip it through at the store!

Thanks to both of you!

I have no experience with cf board but do with rock wool insulation. At first I tried to cut it with a straight edged knife (like I do with regular fiberglass insulation) but it kept tearing.
Shortly afterwards, I found out that you need to use a serrated knife to cut it to produce a clean edge. Just a cheapo dollar store bread knife made all the difference in the world!
As the structure may change a bit to the cf board after its fired, maybe a change in knifes would work as well?

Generally I make clay slip thin enough so that it can just make it through a fly screen mesh without spending a lot of time shaking it to go through. Too much water though makes the clay thinned out a little too much and can throw the proportions off, unless you allow for it. So I guess around smoothie consistency. Preferably blueberry for me please.   :)

Love your tin woman arm! Just be sure to oil it every so often, stay out of the rain and you should be fine.
Oh, just had another thought. This Halloween you could go dressed as a rocket mass heater! A sure way to get lots of candy at your local permaculture party.

Greetings after a long while!
I am back and things have been happening. Past couple weeks were spent on the chimney, but it is installed now and we are ready to go. I ended up using stove pipe for the whole length until insulated (24" for $6!) I’ve started to lay bricks for the outline of the bench and manifold, and filled the manifold chamber with 4” of perlite-clay, the bench chamber with 4” of cob.

The bench will get one more line of brick before the barrels go on, that will happen tomorrow, as well as cobbing in some clean outs.

Then working on the core and manifold, I have my core ready to go so setting that on top of the perlite once dry and and then building brick up around the fuel feed and building up the manifold, and support for the barrel. I will have an 8” pipe as transition area from the manifold to bench.

Curious to see how this is looking to you all, is it a mistake to have the clean outs made of hvac? I wasn’t able to work the T into the base of chimney so i’m hoping to have a clean out perpendicular to the exhaust entrance.

Hope everyone has been safe and healthy.

Hi Sophie,   Great start! Looking very nice.

Can't remember if you said if the floor your building on is a cement slab? Looks like it to me. Not a show stopper, but it too could have benefited from having a layer of perlite/clay as a base too....or just heavy straw cob to help keep the heat from going down and heating the earth. I think you'll be just fine if you keep what you have.

Your hvac cleanouts will also work just fine. They can handle the low heat in the area where they are no problem.

I know a few people who have said that it took a long time before the other end of the bench got warm so they ended up extending the exhaust pipe to the end of the bench which forced the hot gasses to travel all the way down before exiting. This of course would also mean that the current cleanout would be moved further down also.

Sophie, I just saw your post from Sept. 24 about your insulated chimney being 6" instead of 8". I realize it is too late to affect you, but it may be helpful to know that I had a similar situation. My J-tube is a 7 1/2" system with a brick and cob bell enclosing the core, with an 8" square tile/masonry chimney planned. As a temporary measure, I had to run the exhaust out the sidewall and up since I can't build the permanent chimney right now, and had some salvaged 6" insulated chimney pipe on hand. It has worked fine even though there are two elbows before exiting through the wall and the total height from J-tube feed to chimney top is only 12' (17' as of this summer, not tested hard yet).

In general, I would support keeping the flue cross section constant, but I have demonstrated that in good conditions a reduction can still work.

Gone again for a few days but I’m back!
Gerry, I went ahead and lengthened the exhaust. I think the bench may be small enough for it to not be necessary but it couldn’t hurt, and now is the time to do it if ever.

I moved the clean out to the other side of the bench because I won’t be able to access it from the back due to the plans for the room. It’s a little tight but I can reach the exhaust entrance. I am wondering not if it’s an issue that I won’t have a clean out at the 90 degree chimney turn, should I try to work a T into the exhaust once it leaves the bench?

The perlite mix has tried a bunch but bits still come off, so I went out on a whim and coated my ash out with a thin layer of cob, thinking that it will make cleaning out ash easier. I also put down a thin pad of cob where the core goes because the surface need slight leveling. This cob is so thin I doubt it would affect anything but curious what y’all think. If it’s okay, I’d like to cob a thin layer over all of the perlite.

A few other concerns,

My ceramic fiber board seems really soft, I thought after firing it would harden but the charred areas are a bit squishy. The bottom piece, actually cracked slightly, i guess from moving around too much. As of now I’m moving forward anyway, I really don’t want to purchase more CFB. But feeling a bit worried... Maybe wishing I had gone firebricks..

My bench height is at 8 and a half inches now so next comes the half barrels, tomorrow I will cut out of the barrels where the chimney and transition pipe enter. Wondering how to “seal” the barrels to the brick... I have some long skinny CFB scraps I was thinking of setting the barrel edges into those, maybe hammering them in and cobbing around? But maybe just cob is enough?

Last thing, I am a bit worried about my cob.. it’s  either not sticky at all, or if I mix it wet enough it sticks to my gloves but not the brick. I am thinking about wetting the brick before cobbing over it, but maybe my mix is off? I think it’s possible my sand particles are still a bit large even after sifting through window screen.

Hi Sophie;  Welcome back!
Your build is looking very nice!
Let me try to answer your questions.
Cob over your perlite is fine.
Extending the pipe towards the far end of the bell is just a good idea.
For sealing your barrels. If you had ceramic fiber blanket I would say to use it.
As you only have CF board then your cob will work just fine.
The cfb board never gets very hard, but it is in a place where nothing can molest it.
If the riser becomes an issue than you can always make a 5 minute riser later.
Bricks should always be dipped if not soaked in water before cobbing. A dry clay brick can suck the moisture right out of mortar before it can set up.
I'm sure your cob is fine. Once your bricks are wet it will stick to them.
When I built my first RMH I worried about the cob as well. I think everyone does.
Now with many builds and rebuilds under my cap I know its just sandy sticky mud.

I forgot about your cleanout question.
With a piped system cleanouts are very important.
With a half barrel system you may not need to clean for several years.

Checking back in!
Feels like I’m getting very close. Benches are set and sealed, working on the manifold now. I am thinking of using these big (shale? slate?) pieces. To bridge the gaps in order to support my barrel and serve as the lid to the manifold. Any thoughts? They won’t explode will they?

One more question, I saw in a recent post that the 2" gap between riser and barrel top is not always recommended. As is my barrel would have a 4" gap from riser, I was going to cut two inches off the bottom of the barrel but wanted to check in first.

Including some progress pics :

Thanks as always

Also wanted to add, my manifold is obviously huge. I know that too small can lead to problems... but can it be too big?

Hi Sophie; No it can not be to big!    That manifold is wonderful! It looks quite a bit like mine.
As far as top gap. I used a 2.5" gap for seven years with no issues.  4" will be fine if your not cooking on the barrel top.
The slate "should" be fine. Highly doubt it would explode ... but could crack. Just keep an eye on it.
Your whole build is looking very professional!  We will want to list you in the local builders guide !