Why this Cob is Fast

Video 3: Why We Call it Fast Cob!

31/3/2018

7 Comments

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In the next video, I'll show you why our style of Natural Building is called Fast Cob!

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7 Comments

Columbcille Dougherty

4/4/2018 01:50:41 pm

I am very interested in earthen Building, and Cob especially! I live in a cold climate (buffalo, and am looking for land in Maine) so most people keep saying i will need to use straw bale, i would love to hear your thoughts!

Dave Olsen

4/4/2018 08:54:12 pm

Thanks so much for your question. I've varied my answer over the years...I likely would have agreed with the others about 12 years ago. Then I thought a hybrid (strawbale on North side; Fast Cob on the rest) would be best. I still haven't worked with strawbales to build walls, but it seems more expensive in terms of cost and resources than Fast Cob! My experience with cob at -10ºC is that a foot thick wall is too thin. My guess is that 18" walls would work well to both hold the heat and not allow it to transfer right through the wall. If I lived in such a climate, I would probably build a small building with a thin cob wall on the outside and a thicker cob wall on the inside, sandwiching a natural insulator between them. Perhaps perlite? One could even build thick walls and consistently place a think strip of perlite in the last "brick" to mimic what I just dexcribed; this would likely be faster and more consistent. And it would allow both the inside and outside "walls" to be attached, which is important for its monolithic strength, although with 18" walls, you could build as heavy a roof as you possibly could and there would be no issue for structural strength.

And then there's the summers...Fast Cob would make the inside of your building super comfy even in the intense heat that climate change is bringing each year.

Hope that helps!

Dave Olsen

7/4/2018 11:27:03 am

(offline from Columbcille Dougherty): I know you suggested people
Perlite, that's not something I can produce, I try to build able to produce everything, and I was looking around... Rice husk ash has a high silica content, would mixing that into the cob work just as well?

Dave: Yes, thank you for that! It seems like there are more folks under a blanket of snow than those of us not at the moment!
If the husk or whatever you try, doesn't squish and degrade quickly, it should help. You're looking for something that can be coated with clay but still keeps some air within it...that's why perlite works well, since it's volcanic popcorn.

Columbcille Dougherty: What kind of ratio are we looking at? I live not to far from Ontario like the other guy lol

Dave: Well, again I haven't tested this. So my first test would be a small heated building with 18" walls and if I had a material or two to test with, I'd put that in the middle (but in the outside half) of the wall as I built, to see if it makes a difference. Some walls "insulated" with a couple of cm/1" of this material, and some without. And see how it performs.

I really don't think anything is "needed"; I think 18" Fast Cob walls would be enough. If they weren't, then 24" walls. I'm only guessing since I haven't lived in that climate for a few decades...but the thermal mass of cob will keep the cold out and the heat in with thick enough walls...it's when they are too thin that the heat and cold transfers right through, which I discovers happens at -10ºC with 12" walls.

Columbcille

8/4/2018 03:47:31 pm

Do you know if any natural techniques to do earthen sheltered cob, primarily the waterproofing, this seems to be difficult to tackle from a natural sustainable approach

Monika

6/4/2018 09:32:57 am

That is surely one tempting offer, to have a house built and enclosed this year still.
Couple questions:
would you come to Ontario (Westport to be precise)?
would you build bigger than 1000 sq ft. - I am hoping for 1500-2000.
we get -30 C in winter here, would 18 inch cob walls still work - I saw your answer above for the colder climate, but you mentioned only -10
can you use the fast cob method as the mortar if you were doing a cordwood stack - it seems to me that you could go even faster.
Ontario codes for building are pretty strict-have you had any experience with satisfying code requirements with the fast cob?
what would you charge, even roughly, for coming to Ontario to build a larger than 1000 sq ft house?
Phewww....I think I got them all out- looking forward to your feedback
Take care
Monika

Dave Olsen link

6/4/2018 11:49:58 pm

Wow, I haven't been invited to Ontario for a few years now! Thanks so much, Monika!

I have built bigger, in the range that you request, but I didn't have Fast Cob tweaked as well as I do now. So, yes, building 1500-2000 sq ft is within our capabilities.

My speculation with 18" walls was meant to be for -30ºC climates; my only experience with -10ºC was in a tiny home that has 12" walls, and I learned that chilly day or two that 12" walls are not thick enough.

Another difference between Fast Cob! and the West Coast Traditional Cob (WCTC) that I originally learned is that putting smaller items in the wall to displace the amount of cob you need to make (which is critical for the WCTC), often slows down Fast Cob!

Cobwood may not, since cordwood is often flat-ish and sizeable. Before Fast Cob, I thought cobwood would be the way to go for larger buildings. However, all the cobwood buildings that I've inspected show that the wood shrinks away from the cob. Not necessarily a problem per se, but it will requre more yearly maintenance (to fill in those gaps) than a full-on Fast Cob! building, especially in your climate (a tiny draft can make a huge difference!).

And no, I have no experience at all with Ontario codes.

However, since this is getting rather lengthy already, I will email you off-line and explore further with you the dream that you write of...I'm serious about helping you make 2018 the Year of Fast Cob, so thank you so much for reaching out and asking!

Eric

24/7/2018 11:34:57 am

One barrier for me personally is economic-
if you offer a work trade to cover the workshop cost I could be there in August.
I am considering biking from northern California.

Thanks,
Eric

Video 3: Why We Call it Fast Cob!

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