Cob 4 cob questions

[Raduazo at aol.com]

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 1) For a two-person work crew, what would be the optimal size of mixing 
 machine (in cubic yards) for one days worth of cob.
A. The best mixing machine for cob is a rototiller of 3-5 horsepower.  If you 
want good quality control for the mix try mixing on a parking slab.  
 
 2) Using the tarp/pit method, how long does it take two people to make a 
 given amount of cob (for example, hours to make a batch of? cubic yards of 
 cob)?  Any time estimates using other mixing methods?
A. This depends largely on the quality of the clay.  It is very difficult to 
hydrate and begin mixing very dry and hard clay.
 
 3) On an average six-hour work day, how many cubic yards of cob could a 
 two-person crew place on walls (excluding the time it takes to make the cob)?
A. I do not know there are too many variables.  In a project I worked on in 
BC (Canada) we had a crew of 20 people doing all foot mixing (with tarps).  
We were working on a small house (about 15'X20") and had the walls up to 
about 5-6' level by the end of the week.  You can extrapolate from that, but 
you have different conditions so your extrapolation is of little use.
 
 4) On the average, how much straw is added to a mix (for example, pounds 
 per? gallons of cob)?  
A.  I would guess that 1/3 to 1/5th of the volume is straw.  The walls we 
built were 18 inches thick, but here again I am guessing.

	In experiments that I conducted at a cite in Tacoma Park MD. I found 
that a rototiller just about doubled the amount of cob that you can mix on a 
tarp.  This is because the tiller mixes up sand and clay and tends to form a 
granular mixture which can be quickly hydrated.  We did the final mix on a 
tarp because the builder wanted "quality cob", but I believe that the foot 
mixing could have been eliminated all together and the moving and loading 
could have been done with a dirt fork and wheelbarrows.  Since you are 
working with only two people this might be important.
Ed