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stinky clay

 
pollinator
Posts: 158
Location: Western Idaho
48
earthworks greening the desert ungarbage
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I've finished the foundation and the lumber is coming but I've been doing some tests with some of the clays on the property here for a rammed-cob wall system for my cabin I'm building and the clay deposit near the spring gets kinda stinky when it's wet. It seems to be the best however, it is incredibly hard when dry, almost like concrete but it has a slightly boggy smell when it is wet. Anaerobic funk I assume but my question is if this odor is a sign of something that could lead to a structural disadvantage in construction. It is odorless when dry. Also, could I add something while mixing the cob to "disinfect" the cob and get rid of the smell? hydrogen peroxide maybe? has anyone ever built with kinda stinky clay and still had good results?
 
Posts: 539
Location: Abkhazia · Cfa (humid subtropical) - temperate · clay soil
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This is actually what is done to make it stronger: Fermenting it with grass. Smells a lot, but gets really strong.

I would say that you found a good plaster. It should be waterproof.
 
Posts: 793
Location: In the woods, West Coast USA
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The clay will dry out and not smell.  If you are concerned about it, you can partially dry it out in a thin-but-wide section (meaning dig it out, put it on top of dry soil) for a while under a tarp until it gets to that point where you can make it fall apart with a shovel, at which point it should smell better.

If it is smelling anaerobic  hopefully that's not too close to a foundation, even for a shed.  There are often several facets to a spring and large amounts of ground water close to the surface in the vicinity in the winter, so even if you are 25 feet away from the spring, the ground under a building could start to sink under wet clay that smells that way.  The soil may look dry and solid  in the summer, but is very different in the winter.   There are probably berries and trees growing in a line showing how the underground water runs, and it's best to build as far away from that situation as possible.  
 
Cristo Balete
Posts: 793
Location: In the woods, West Coast USA
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Now that I think about it, if there's any chance of a kind of wood mold getting into the framing wood, then it's safer to not use anerobic-smelling clay.

Nobody will want to hear this, but for the last 5 years or so I've been staining all non-treated wood before I use it, particularly the ends, and it's holding up much better than bare wood.  I can get discount gallons of stain at the DIY store when people don't want what they've ordered, usually custom colors.  The store will sell it for less.  Stain penetrates better than paint and helps protect against wood mold.

 
Aaron Tusmith
pollinator
Posts: 158
Location: Western Idaho
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hey thanks, I did end up reading about the fermenting process which I thought was very interesting. Not to worry about the building being close to the spring, the spring is just the source of my clay, good tips though, thank you. So what about the staining? I am shooting for this to be a natural building -as much as possible. Would it be best of I were to treat the wood that will be in contact with the cob? The plan is conventional framing with cob infill between the studs using temporary forms.
 
Cristo Balete
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As much as I love natural things, 30 years down the road of projects in a rural location I've done enough redoing on sheds, a dock, wooden window frames, decks, grapevine poles.  It's inevitable.   I don't hesitate anymore to use treated wood in an exterior application (the dock,  a shed in contact with soil, wooden fence posts) because if the wood is bare it may only last a few years.  I'll probably get more brain tumors from sitting in front of a computer screen :)  The cost of replacing wood is expensive.  It's probably tripled since I first did the projects.  I don't mean to say that treated wood should be used in a building frame, it shouldn't, just when in contact with soil.

A solid-color polyurethane stain will penetrate, and while it isn't perfect, it gives some protection without too much unnatural stuff.  There will also be plenty of cob around it, with straw that absorbs any off-gassing.  I would be more concerned about the off-gassing of synthetic carpets.   There's also a mold additive at the paint store that can be added to paint and stain, then applied.  The shady side of a building (north in the northern hemisphere) will be more vulnerable to moisture/mold/moss.  If you have a shed or a house there now, check the roof and see what's growing on it if it's been there 5+ years.

At some point there's going to be a weak spot where blowing rain gets to the cob, or wet and eventually dripping snow, which means dampness gets to the wood.  Or dampness coming up from the soil will get into the wood, into the interior.   There will be a lot of tweaking, unless the building is in the desert.

Not everyone has termites, but if they are around, they are quick!   If wood stays damp enough it will get moldy.  





 
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