I know that what I am about to say is not a very green idea...has anyone ever considered using a waterbased marine grade verathane or acrylic in straw instead of clay slip as a preservative? My reasoning: if it would work, it is a more quantifiable material for building inspectors and codes..also would be easier for first time builders.
To me it be like comparing apples and oranges. Verathane or acrylic are water resistant synthetic or polymer film,, clay is hygroscopic with a large surface area and pore structure internally, straw needs to breath and intake and release vapor through it's tubular shape, and it's binder needs to be hygroscopic. It may yield an interesting mix only lab and field test would reveal. As far as being "more quantifiable material for building inspectors and codes" again, required testing if there is even a test standard for it otherwise ASTM would need to create one, then a International code compliance (ICC) letter, then it make it's way in the 2015 IRC Appendix R "Strawbale" or it's own appendix, then local jurisdictions would need to adopt it.....at that point which is a VERY long haul, it would be "more quantifiable material for building inspectors and codes". Actually, there is a lot of quantifiable data on clay-slip...we know it performs best at 13lbs.ft3 when thoroughly mixed by machinery and has an r-value of 1.7/inch.
John Straube, PHD, has done alot of testing on clay-slip and strawbale search for "Breathable Walls" thread.
I do agree though more needs to be quantified with mass in general and clay so people understand it better. Orlando, FL National Labs ORNL has done some with portland cement concrete to give an idea of clay/lime affect on HVAC loads lowering them in most US climate zones, etc..... Most assign r-values to mass since they do not understand it which is very misleading.