We're new to cob and took it upon ourselves to make a modest cob structure this summer- erecting cob walls around a pre-existing covered patio beside a garage. All was going smoothly; we had figured out the perfect ratio of native soil to amendments (clay powder, in our case) based on multiple test bricks and shake tests, and had a solid 18 inch urbanite stem wall over nearly a foot of gravel.
I should clarify, by "we", I mostly mean a couple who have been our wonderful, hardworking, cautious and conscientious WWOOFers for the summer. Over 2 days they built up about 10-12 inches when they began to notice small cracks that hadn't been an issue with any of the test bricks. Being the cautious folks they are, decided to halt consturuction for the time being until they could research further, consult a friend with some cobbing experience, etc. They put tarps over the finished walls, and my family and I spent 11 glorious days in Montana, confident they'd have everything figured out upon our return.
We returned today and our otherwise great work-trade partners haven't been able to gain much insight into how concerning these cracks should be, and in fact hadn't even checked on the cob while we were gone. It appears that there is some mold growing on the visible straw, not a great deal, but its definitely there. So...i have two questions:
1. Are small cracks a dire concern? The walls are not load-bearing, so my suspicion was that it'd be okay. They're definitely solid (i gave them several strong kicks and they didn't give at all)
2. The mold! Ick! Is this a cause for panic? Of course, the year we choose to do a cob project, Portland has an uncharacteristically cool and moist summer (which has wreacked a mildwey havoc on my comfrey), but it sounds like there are some hot (upper 80s-90) days on the horizon. Will a few hot, dry days knock this out and allow us to stay the course? Do we need to start over? Treat it with something antifungal? Help!
mold: this is straw that was sticking out of the half built wall? that will be built in later? and then you'd plaster over the top of that? don't worry about it. don't USE moldy straw, but if it was good straw and a couple weeks exposure had some mold show up, no big deal.
and this is a exterior wall around a patio? will this be enclosing part of your future living space, or just some sort of patio wall thing? if it's just an outdoor furniture feature, really don't worry about it. if it will be a future bedroom or something, just make sure to have that moldy straw deep inside the wall. and try not to let it all get like that.
cracks: little 'hairline' cracks are no big deal. cracks you can put your finger in are a big deal. if you can stand on the dried, cracked sections without them collapsing under your weight, they're fine.
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