Hi Rick,
Whichever method you decide to create straw bales, make sure it will give you bales of the density required by the building code applicable to your area. Several European countries and the U.S (and I think perhaps Australia and New Zealand?) have evolved building codes to guide the construction of structures with straw bale walls so they perform (thermally, structurally) as expected.
In the U.S. the minimum density for straw bales used in a wall assembly must be 6.5 lbs. per cubic foot.
It's an easy calculation if you have a tape measure, a weight scale, and a moisture meter: (1) weigh the bale, (2) measure the bale's volume by multiplying it's three dimensions (height, width, length), (3) average a few moisture readings taken with a hay moisture meter and subtract the % of moisture weight from the bale weight, e.g. a 50 lb. bale with 10% moisture content would have around 5 lbs. of
water in it, meaning the bale has a 45 lb.
dry weight, (4) divide the bale dry weight by it's volume ....and you'll know if the bale meets code-level density requirements.
For example, a three-string bale in N. America might be 23" wide x 15" tall x 48" long. That's 16,560 cubic inches, or 9.58 cubic feet (a cubic foot is 1,728 cubic inches). If it has an 70 lb. dry weight, it's dry weight density is 7.3 lbs. per cubic foot.
While bales that are less dense have almost certainly been used in straw bale buildings since it all started back in the 1890s when baling equipment reached the Great Plains of America (this code is relatively recent, and bale buildings have been around for a long while now), testing shows that meeting the minimum density requirement results in better thermal performance, and if the bales are used structurally, a more stable wall.
Jim Reiland
Many Hands Builders