Conner Choi wrote:Hi there,
I'm building a cob house and I have plans and everything but I'm having alot of trouble finding the right kind of straw this time of year. I've read that rice straw and many other straws are unsuitable for cob construction because they lack the tensile strength that is present in barley, oat, and wheat straws. Can anyone validate this? I have alot of long dry grasses on the property I'm building on, would this be suitable?
Any help is appreciated.
I do not see in strawbale building code that rice is excluded, meaning code provides a "prescriptive path" that has been tested and passed the test of time:
http://thelaststraw.org/wp-content/uploads/IRC_StrawbaleConstructionAppendix_Approved_10.4.13.pdf
AR103.7 Types of straw. Bales shall be composed of straw from wheat, rice, rye, barley, or oat.
AR103.8 Other baled material. The dry stems of other cereal grains shall be acceptable when approved.
by the building official.
It is the highest silica content you want, hemp is very high 80%+. Silica composes 71 percent of the
ash of Equisetum telemantia, 51 percent of the
straw of barley, 67 percent of the straw of wheat, and 46 percent of the straw of oats . The
native grasses and weedy grasses as well as the cereal crops have varying amounts of silica.
If you wanted to spend the money you could have atterburg soil test, or if do you know how to do a jar test to get an idea of how much binder is your soil that will determine how well it bonds to straw or grass? If it is low you can add cements like fly ash, lime, portland cement to stabilize it and made it stronger. You could take a sample you make in PVC pipe about 5-6 inch in diameter to take to a lab for compression testing if a code official wants it to satisfy a building permit. Or, if no building codes just make up a wall and stomp on it a few times you'll get a feel fast for how strong it is and whether it cracks. Test some sealers on the test sample too or any other renders you are planning on.