Rethink Your Life!
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Kiko Denzer on Art

[Cob] update on trench issues

Tim Nam tkn317071 at
Tue Aug 19 19:40:30 CDT 2008


I decided to not tie in to the existing drain line, opting instead to tunnel through the existing trench (of strawbale garden wall), to daylight, affording my trench an extra 3" of depth, well below the 12" frost line here in the Willamette Valley.

So the plan is: slope the bottom of the trench to daylight, put in some 3/4" minus on the bottom then the drain pipe with the 4" minus clean, river rock. I think I'll add some smaller concrete chunks and chunks of asphalt which were kindly left here by the previous owner (yes, hint of sarcasm) but I think a good use for it, as rubble that is.

So I'm still wondering, what do yall think about whether to line the trench with a poly lumber tarp? that is, to slow siltation of drain rock and pipe and deter root penetration/heave. My concern is the tarp though used, is still in good shape, and that it won't be porous enough...perhaps landscaping cloth will work better?

And about the issue of concrete and rising damp, I was planning on a mortared urbanite stemwall, do I need to have a vapor barrier between the urbanite-cob junction? 


----- Original Message ----
From: Damon Howell <dhowell at>
To: coblist at
Sent: Tuesday, August 19, 2008 1:37:55 PM
Subject: [Cob] off the concrete subject

Ocean was right in saying it was a silly question about straw in  
concrete. I didn't think of it causing such a stir either, but we may  
talk about what we feel needs attention, and anything to do with  
concrete gets cobbers going every time. But unfortunately, cob has  
it's place, and on the ground isn't it. I have done quite a bit of  
reading on Roman concrete, which is made from lime and volcanic ash,  
mixed extremely dry, then packed into forms. The process was pretty  
much like rammed-earth and it's still there 2,000 years later. Cob  
doesn't really lend it's self to compaction. Just like in concrete,  
cob is stronger the drier the mix. But I've noticed when I mix dry I  
feel like the clay doesn't bond and will not form a solid structure.  
If I pack it, it bonds, it just doesn't seem to stay together as  
well. Can anyone enlighten me on this?


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