Yes, good video Tom thanks!....My take away's are not any straw will do, it needs to be controlled just like bales are to prevent "microbes". He presents some good data on the "sweet spot" of 50/50 mix of clay to straw to get the "13 -lb/ft3" and R=1.7/inch....Bale code calls for 6.5 density, add the same weight of clay(40% min as lab tested), and water to pass his "cigar test".
Real interesting the role the clay plays in keeping the moisture content of the straw and microbes low, and how the thermo-couples showed heat from them metabolizing and combustion when straw gets wet, they keep it wet. When in a slip clay wall they don't like it, want out so it dries faster than straw alone.
I don't like the 3 month dry times, no fenestration can be installed for drying purposes, but, he did say a high perm plaster that would not keep the wall from breathing or drying could cut that construction time down.....I bet that is what he tested further? In summer and a high Relative Humidly I would think the wall still will not dry that fast, dryer climates faster.
Anyone understand the mixing process and equipment, that is where I got a little lost, and associated cost in it and labor say to bale construction?
Maybe a bit offtopic, but I have a dilemma and I have to make an urgent decision due to a limited offer for straw bales of einkorn wheat.
The question is about the type of straw in terms of grains family plants. As I want to start a light clay and cob walls in late April and currently I have just this one choice of straw type - einkorn wheat (Triticum monococcum) I want to ask you all if you have any knowledge about the appropriateness of einkorn wheat for cob and straw clay building.
The straw itself looks very bright and yellow, but is it strong and in all other aspects good enough for mixing with clay?
Thanks for the help!
posted 5 years ago
Ivan, my understanding is the higher the silica content the better, that is why hemp is so good it is very high (80%+) (it can grow in high sandy silt soil and tall giving it high tensile strength), next is wheat (~60%) that chemically bonds with clay silica, etc, depending on type. I can't imagine it varies alot with family member, or we'd see warning's in our new "international" 2015 bale and clay-slip building code. Only a lab could answer your question fully if you want to pay for it, not that expensive here, and the video recommends it for clay content. If you don't want to take that route or it is cost prohibitive where you live, make up a test panel and see how well it holds together. The cellulose fiber tensile strength holds the clay/lime/etc binder together, the tubular straw drains and evaporates water. Remember the final mix is insulation, non load bearing so it does not have to be "strong"....the great thing about it though compared to other loose batts is when in-filled between timber framing it does provide some shear and racking resistance. Good luck, and follow the video's recommendation for color (which yours is yellow, not green so good) and moisture content/drying, mix ratios.
It was nice to see a chemist put some logic to clay-slip and validate the r=1.7 / inch and mass benefit controversy.
Thank you very much for this valuable information. So based on your logic I shouldexperience no difficulties using einkorn wheat. Actually I plan to use it for both straw-clay and cob, together with oat straw, which in particular is described as suitable for cob in Ianto's book.
Another topic I'm stil not sure about is the "maximum" width of straw-clay wall which is "safe" to build. Safe in terms of moisture. Although I'm planning to build the wall in the hottest part of the year, when usually even night temperatures don't drop under 20 degrees C (and day temps are often above 28-30 C), I was told by some experienced earth builders it's risky to build straw-clay wall wider than 15cm. My wish, however is at least 17 or even 20+ cm. Does anybody have practical experience in such widths? According to the video, it seems to be ok, but still?
Thanks for the help!
Diego Footer on Permaculture Based Homesteads - from the Eat Your Dirt Summit