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Working with cob in winter?

 
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When I worked in concrete there was a great deal of concern for working in the winter lest the concrete would crack or "pop up" and fall apart. Can the same be said for cob?

If there was a necessity to work with cob with wattle and daub in the winter would it be possible to do without hindering its integrity? What would be the lowest temperatures to work in?
 
pollinator
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http://www.greenhomebuilding.com

From above-
Q: I am interested in building a natural home in central Vermont. I am very interested in cob but am confused as to whether it is a good choice for the climate of central Vermont. What do you suggest?

A: Like other earthen wall systems, cob does not have a very high insulation value per thickness (less than R=0.5 per inch.). One way to get a higher R-value is to build a very thick wall.
The traditional 3-foot-thick cob walls in Devon may have the equivalent of R=15 or so. The problem is that in a very cold climate such as yours, all that mass will be constantly losing heat to the outside, especially on the north side of the building and other parts that never receive direct sun in the winter. (If the wall gets regular sun on the outside, solar warming will make up for some of the heat loss.)

Generally I would not recommend using cob for exterior walls where winter temperatures stay below freezing during the day. However, there can still be a place for cob in every climate. As interior walls, surrounded by a highly insulating envelope (such as straw bale), a massive material like cob helps to maintain a consistent interior temperature, preventing both overheating and overcooling. An especially efficient place to put your thermal mass is close to your heat source, so build a sculptural cob hearth and mass wall around your wood stove.
That's my suggestion for very cold winter areas: cob for interior walls (and possibly south-facing exterior walls if you get very regular sun through the winter). The only exceptions would be for buildings that don't need to be heated or if you are building a very tiny building, in which case the amount of heat lost through the walls may be negligible anyway.
 
Nathaniel Swasey
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I don't know much about cob, but I'm assuming that if I can work the materials into a mix and put them in place that I would be able to work with the temperatures as long as it's not freezing. Am I wrong to assume this?

From what I understand, the Anglo Saxon nations were building houses of wattle and daub in England and in the Scandinavian countries, which share the same weather I have here. I feel certain that, while it might be uncomfortable, it would be a way to carry a family through a winter. There were historical buildings here that used a type of paper, or a material nearly as thick as paper as their exterior walls and no insulation, yet they lasted the winter.

Also, my ancestors came to this continent in the 1650's and lived in clap board houses when they got here in the winter. Surely cob would have been preferred?

I can't say that I will use this information or not, but I feel that having this knowledge would be empowering if I ever did need it. But I am having a hard time finding the information as to how cold can cob successfully be worked? Most of what I find discourages the work because it's not comfortable.

 
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I live in a climate as cold as Vermont, and our rammed earth houses, which are essentially cob in forms, are good for this climate. Some benefits, some drawbacks, but generally good. I really like how the thermal mass holds heat or "coolth" for weeks, even months as the seasons change. And because it is so thick, it does actually insulate well.

But building with wet earth in freezing weather? I don't think it's a good idea. The outer layers will go through freeze thaw cycles before they dry, making them crumbly. And working with cob or earth tends to be wet chilly work.
 
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I have been using clay/sand mortar for my masonry heater. I would say so far it has worked great for mortar. It is currently around 1* C outside where i have been working. We even have some snow on the ground.

If it was frozen i would probably not be trying to use the clay/sand. In my situation the clay/sand mortar becomes quite dry from the red clay bricks. I am not sure what a cob wall would do.

I am also sure the cob would be really cold to work with your hands. I am using a trowel to put mortar on.

In my opinion if your weather is going to hold above freezing i would say go for it. Below freezing i would say wait til spring.
 
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Because ice is approximately 2% less dense than water, it thus has a larger surface area......  depending how how much h20 is in the cob and how much freezing and thawing you get, i would count on structural integrity a bit disrupted before final hardening and curing so to speak...
 
Nathaniel Swasey
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Thanks, you guys. This is the information I was looking for and I suspected as much. Now I have to figure out the cure times of cob based on temperature.
 
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Hello Nathaniel,
I'm in Vermont and have similar concerns. I know someone who built a rocket heater in an unheated garage and it froze before it cured. Yes, it fell apart. No surprise.

What gives me fits is how extremely long it takes a thick cob wall to cure completely. I think it's more than a year before *all* the moisture is driven out. If you had it up, dry to the touch, load bearing, and roofed over (at least a month's cure, I'd think) then so long as the house were heated from within you'd probably be okay. But if you only got partway through the project before winter locked down, I don't think you'd have much structural integrity to work with by the time spring arrived. You'd be under a brutal time clock. In the North, you'd basically have to finish the whole mudding part of the house between the end of May - the end of August (or maybe September given climate change) and then have the roof on and the stove fired up by mid-Oct at the absolute latest. Three, three and a half months to move all those tons of mud. Ouch.

And also, I do think you wouldn't want a mass house in a cold climate without some heavy duty insulation, and insulating a curvy cob structure can be a challenge. I'm trying to come up with a better perlite plaster solution than I've heard of yet ( https://permies.com/t/170809/Properties-perlite-waterglass-plasters ), and trying to avoid building out a second wall and stuffing the cavity, though that might work for you. It's encouraging to hear from Rebecca with a comfortable rammed earth house in a cold climate, but still, around here the "average" of seasonal temperature variations is ... pretty darn cold.

Like to hear what you come up with
 
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