Check out Hemp Adobe Homes on youtube and their website. He claims it is so good it heals itself if it is cracked because it draws in carbon. Very futuristic stuff yet simple and it sets up in 2 minutes! I don't think you really need the hemp because its the Magnesium Oxide and the Phosphate that does the trick. Portland cement wont bond with cellulose but this will. So you could use straw and wood chips and it would be more insulating, stronger and lighter. In ancient times I guess the manure was a source for it to bond with and it had the phosphate necessary to set up with the MgO. If I had the money I'd experiment myself on ratios of what to put in and such.
Here is a source apparently for Magnesium Oxide
https://www.uswatersystems.com/flomag-magnesium-oxide-media-corsex.html?fee=10&fep=1728&gclid=CNaki5L9oMsCFQ6oaQodTmkMfA
I've heard ashes are used in certain quantities but for what reason I don't know. If anyone finds out the ratios of MgO, straw/woodchips and manure or a different phosphate source please share!!!