[Cob] key in the concrete beam

[dhowell at pickensprogressonline.com]

Anna: "you could set big stones in the concrete as it gets poured"

I've thought this same process. It seems like the best way to me.  
Embed large stones on the top of the concrete while it is still wet  
and let them sink in a little. This provides that rough surface for  
keying but doesn't cause a "low spot" so water can be trapped. It is  
my thoughts that since cob is porous and does transmit water, then  
even if it does dry out fairly quickly, the rust will eventually set  
in on the steel and completely deteriorate it. That causes gaps which  
will probably cave in under pressure and cause severe cracking.  
Stones embedded in wet concrete will not move, and cob built up  
around those stones will not move, so you have a product that will  
not move. Why is there such an infatuation with steel rebar in the  
building industry? I've seen in the past where a concrete bridge was  
torn down and they found that the rebar had completely rusted away.  
So, really this is a good material to use, even in concrete. Think  
about it; concrete absorbs water, but because it isn't porous it the  
water doesn't evaporate. If there is steel in there there will be a  
reaction!
Damon