Questions about my build...

[rjdudley]

Alright so I'm preparing to build my RMH in my house and now have some questions:
1) Ianto says to lay crumpled aluminum foil, glued to the floor. Should I? Or should I put durarock?
2) I will be putting 4 inches of cob under the exhaust pipe. Question should that be cob or just clay or cob & perlite?
3) If I lay the exhaust pipe on top of that substance and then place "urbanite" around the pipes how do I get the cob stuff in all of the crevices? Isn't cob a fairly stiff product? I mean, we don't air in the bed correct? Air is an insulator not a conductor. Have I got this right? If so should I make some of the cob more "watery" to fill the voids?
Anyone? Matt? Manny? Looking for a lifeline here
Ray

[matt walker]

[mannytheseacow]

Yeah I was curious about this when I started too. Once I started filling it in it all started making sense. If it's too dry add a little water. All that water has come out at some point but the thinner the mix the easier it fills in the gaps. Either way it's a time consuming process pressing the cob into the little spaces between everything. Once I got over the enormity of the task I got comfortable going very slow and making sure every little void was packed tight.

Funny story: I had access to a good amount of gravelly material with some dry clay soil mixed into it. I was getting comfortable with two 5 gallon pails of this dumped into a wheel barrel, add a little water, mix it up.... presto. Worked great for a couple days. Then we got rain one day and I had some rain in my wheel barrel. I looked at it and thought, "well shoot, no sense running the well or bringing water up from the rain barrel, I'll just use that water that's in the wheel barrel already; looks about right." Two buckets of material go in and SPLASH! Crap, there's a lot of water in there. Ok, I'll dump another in. I ran myself out of material and it was still like a mashed potato consistency. I had filled the wheel barrel to the brim and it was still too loose. I had to shovel some out, then start mixing in anything dry I could find. I little sand, some leftover fireclay, a scoop of portland cement. I ended up with more than two wheel barrels full of material for the bench that night, and it was still a little looser than I would have liked. Moral of the story: a little water goes a long way.

[rjdudley]

Thanks for the info guys! Great story Manny, I know for a fact I would have done things the same way!
I've got the carpet pulled up and I'm getting ready to put down the durarock/brick/durarock sandwich.
Manny is using bricks to form his bench, do you think I need to build a form, maybe of plywood (a temp. form) or can I free-wheel it? That is, making walls of cob say 4" high and then filling that with cob, laying the exhaust and continuing up?
Ray

[mannytheseacow]

Either one will work. I really liked Oddmar's work- the way he framed it in and made the plenum out of metal. Matt's is really cool too, I like the natural stones and cob. Really it's whatever works best for you and what you have on hand. Look hard to scrounge up what you can and you'll guarantee a functional piece of art that represents your personality (and tells a great story)!!

[Lollykoko]

Ray, how about chicken wire or something similar to contain the mass? It seems like it would give you an adaptable base for the first layer of cob to adhere to.

[matt walker]

[rjdudley]

Well what's your feeling/thoughts about wood frames? Does the cob get too hot for wood? My wife would like the bench to be framed with rough sawn boards like our interior walls, but, you know the fear I have of burning my house down.
After watching your latest updated video (Matt) you stated on there that you could frame the bench with wood. No fears there?
Or perhaps I could frame the bench with hardibacker (or would durarock be better) then apply the wood to the hardibacker?
Or would 4-6 inches of cob be fine.
BTW, here's some photos of my progress (questions to follow):
This is the brick work to allow ventilation around the bench.






Alright, does this look like overkill to anyone else? Ianto says 4" spacing and so that's what they are.
And if I have to have this type of protection for the floor/walls wouldn't a wooden frame be just as worrisome?
I wouldn't mind taking some bricks out and saving some weight since another layer of durarock will be on top of these bricks. Can anyone tell this is my first build? Questions and concerns by the bucketful.
Ray

[mannytheseacow]

Check out Oddmars build:

I can't speak from personal experience, as I'm a newbie, but Oddmar's seems to be working for him. Your progress looks awesome. Your brick layout looks pretty precise! Better safe than sorry, ya know? I wouldn't hesitate to lean towards the side of caution. Personally, if I were building with rough boards (I actually considered doing this too, before I found my bricks) I'd probably use cement board and then mount the wood to the face to dress it up, though I don't know that you would necessariy NEED to use the cement board.

I love rough lumber, I'm totally stoked to hear you are doing this!

[matt walker]

Ray, your brick layout looks great to me. It's more about distributing the load than it is about fire protection in my opinion, although the air space is important to the latter. I gotta say man, every build is unique, and you are going to have to satisfy yourself that your installation is safe. That said, I can't really feel super comfortable advising you to put wood on the sides. I have it on mine, in places where I am confident it will never reach high temperatures, like at the far end of my bench as a bookend. If it were me, and I really wanted a wood finish, I'd probably do what you and Manny suggest. Face it with hardibacker, and run it for a while. Get a feel for what kind of temperatures you are seeing and where. Once you are totally confident in your plan you can move forward with the finish facing. I do suggest it in my video, for an outdoor system that is run intermittently. There's places on my indoor heater where I put wood without hesitation, and there are other spots on that heater where it would be a terrible idea. You'll have to get familiar with your system and make that call with full knowledge of how it runs.

One thing I learned as I built mine is that a lot of the "hard questions" really answered themselves as I went along. Don't worry, I'm glad you are asking a ton and thinking about all of this stuff so thoroughly. I'm just trying to encourage you to keep putting one foot in front of the other doing your best to be safe. One of the coolest things about these systems to me is their flexibility and adaptability. I have no doubt you are going to create a system that you are completely comfortable with, and understand completely.