Updated NH RMH build w/PICS!!!

[matt walker]

Manny, I had the exact same experience! I expect you will too Ray, once you are a little farther into it. By the time I was finishing my bench I was digging drainage ditches and using whatever came out for the bench mass. I started out worrying myself silly over which clay and ratios and everything you write about there Ray.

What Manny and I both figured out Ray is that most of our soils are already a pretty good mix. Go to a spot near by your work area where you can dig. Clear away whatever is on top, grass or forest duff or whatever so you can see the dirt. If the dirt looks like you want to plant some veggies there, dig deeper. Once you get to the subsoil, dig a pretty good pile of that onto your cobbing tarp and add water and start stomping. I bet you'll find that you have a pretty good mix naturally without having to do too much combining of sand/clay. You can work a lot faster this way and quickly make large batches. Trying to mix clean clay with clean sand is a frustrating process. Like Manny said, once you get it wet enough you can then tie it all together again and dry it a bit by adding in the straw. I don't really pull off a clump as much as make a ball, or a "cob", and toss it back and forth between my hands to bind it together as I head for placing it.

A little clay/sand bedding is the perfect way to fit a riser, in my opinion. Glad to hear you got a good burn going, amazing what a difference that insulated riser makes isn't it?

[rjdudley]

Thanks for all the feedback! The clay/sand ratio thing is one of those rabbit holes. You start looking for info on the web and 10 different sites tell you 10 different ways.
We do have VERY pure/clean clay. It comes from a local clay pit. It seems no matter what ratio we use it still cracks after drying. Was cracking an issue along the way for you guys?
Another thing came up today. When I was looking at my heat riser from yesterdays burn I notice the 8" pipe buckled at the seam near the bottom. Here's a couple of pics:






Do you think this will be an issue? Or affect the burn? I know the measurements of the riser/burn chamber need to be pretty precise.
Thanks
Ray

[mannytheseacow]

Yeah, all my different cob mixes have cracked when they dried. The finish plaster will cover that. At least that's my story and I'm sticking to it.

As for the heat riser... I might be concerned about that. It's hard to tell how your cross sectional area changes with that but it looks like it might be quite a bit smaller. On second look- maybe it will be okay since it's just on the bottom and you're going from square to round there anyway. You might just want to build with it and if it gives you an issue you can take it apart later and fix it. That's one of the easiest areas to get to.

[matt walker]

Yeah, Manny's got it on the cob. Cracks typically mean you need more sand, but they are a part of it. I just kept stacking layers until I got to the plaster, then only worried about the cracks in the visible locations. Underneath my seat coverings it's cracked as can be. No worries, since you build it in layers no one crack is going to go all the way through.

As for your riser, partly it looks like it got a bit deformed when packing the mix. I suppose we could recommend to future builders to put some scraps of wood across the diameter of the flue pipe in places to support it from deforming. I would be inclined to not worry about it Ray. It looks like you have full CSA still, just a little out of round. No big deal. Part of that as well is the beginning of the thing deteriorating from heat. When that happens they always go through a rough burning patch as the flue pipe distorts and starts to fall into the burn chamber, blocking the passage way. It's part of the process, eventually you'll be pulling that flue out of the burn tunnel in little tiny black pieces. Keep on moving forward Ray, you are looking good in my opinion.

[rjdudley]

Gentlemen, once again your words bring peace and comfort!
Tomorrow, Friday, I will assembling the burn chamber, heat riser, barrel and duct work together. Nervous a cat in room full of rockin' chairs.
We are just hours away from having a functional, although not fully cobbed, RMH. And good timing, too. I have a tour coming by on Sunday to see the beast in action.
Seems there's some interest out here in NH for this. Maybe just idle curiosity, maybe some real interest. We'll see.
Thanks for all the hope. This is going to be a BIG weekend.
Ray

[pa_friendly_guy]

GOOD LUCK Ray, I am sure things will go well for you this weekend.

[rjdudley]

Well, it's been a busy, busy day. First up are pictures of the build in progress. Then I'll discuss the build and ask a question.
This is just after hauling in the burn chamber:


After we built the manifold and attached the heat riser:


An inside look at manifold:


A wider view of the build with the exhaust pipe attached:


The barrel added and cobbed in:


Ok, so here's some insight from the build so far. Man, this is work!
That burn chamber is damn heavy and so is the heat riser. Putting these things in your home is definitely a two man job, minimum.
Next, I had an issue with the firebricks for the barrel to sit on. Apparently I didn't take into consideration the thickness of the bricks and ended up having to move the whole burn chamber/heat riser/barrel assembly forward several inches. This had to be done to make sure there was maximum room in the manifold for the gases to flow. Without moving everything forward the bricks "pinched" the manifold closed on one side due to the 8" pipe.
You may notice that there isn't much cob showing around the brick work. I had extra furnace cement/refratory cement and since the bench isn't filled with cob I was afraid we might have gas leaks when we try to fire it up tomorrow. So everything I could touch (seams, butt ends, places where cob meets brick, etc.) got hit with the cement.
I've read where Ianto talks about doing a test burn, but, I don't get how you would do one without having almost the whole build done? The cob bench would have to be completed to keep any loose gases from escaping so alterations would be tough, I would think.
Now, looking at the pictures you can see the 4 inches of bottom cob. Then the duct work. But, where does the urbanite go? It can't fit on the outside of the pipes because there's only 3-4 inches of room and I thought I had to have that much cob there.
It could go between the pipes, but, there wouldn't be much of it. Again there's only 3-4 inches of space there.
AND if I put rock, urbanite, etc. between the pipes and the pipes eventually burn away (as I believe they're supposed to) there won't be any cob "tunnels" for the gases to flow through.
Do I need the urbanite? Would the cob be enough thermal mass on it's own? I'm stumped.
I defer to the experts once again.
Ray

[mannytheseacow]

Wow! Awesome progress you are making, Ray! That RMH is gonna be badass!
My pipes are only 6" so I had a lot more room for large chunks of rock and urbanite. I made sure to cob in all around the pipes but after that I filled as much as I could with big chunks.
I also think its awesome you're having people over to see your work. Even if its just idle curiosity, you're planting seeds!

[matt walker]

Wow Ray, that looks great man! No reason you have to have urbanite, it's just a convenient filler if you have big voids you don't want to mix cob for.

Ray, what are the daytime temps where you are and what is the ambient temp inside where you are building the stove? You are going to want to have some difference between the outside and inside temp, with inside being warmer, or you should expect a rough start and chance of it not working. Not trying to burst your bubble here, but remember Manny joking about trying to light his up in summer? I think you can get it going, but you might want to prepare your guests and yourself for the possibility it won't work. This is a tough time of year to be testing stoves.

[mannytheseacow]

I agree with Matt. I'd wait til you get comfortable with running it before showing off how great they can smoke up your house!
It's good to explain the RMH concept, though, and you are at a great spot in the build for people to understand the inner workings. From my experience with having educational groups that's the hardest thing- just for people to understand what's going on inside.
I don't know the dynamics of your heater, but mine will demonstrate its rockety abilities with a single sheet of newspaper. So I've been limiting my demonstrations to this and explaining the temperature gradient required to get a proper draft. People are always impressed with how fast and hot the top of the barrel will get with just a single sheet of newspaper.