This technique was developed to reduce the amount of fill with loose straw or straw/clay required when the bent (rounded) sides of the bales are butted together. The purpose is to remove the bulge on the ends of the bales so that the bales are squared up and fit right up tight together.
Prepping the bales before stacking them can help make them nice and square. Do this somewhere away from the house or building for fire safety, to keep the dust away from other workers, and to collect the loose straw that will be created. Start with a large number of bales. Use a couple of other bales to help hold one bale stand up on end. With your chainsaw, cut downward a few inches next to the strings on the end of the bale and move the chainsaw out toward the edge of the bale. The bales may have a little roundness between the strings, so clean that area up, too. Try and keep your chain saw level, and don¹t hit those strings! Step back to eyeball it to see if the bale looks square. Clean up 6 to 10 bales, then set the chainsaw down and flip all the bales over to stand them up on the other end, and do the other side. You may have to lay the bales on edge and, with a little jump, put your knee into the bale or hit it with a sledge hammer if it has a curve to it. You could also lay the bales flat on top of a bench, if you don¹t want to bend over or want to keep the bale stable (another person working with you can help make this work easier, too).
You may occasionally hit a string with your chainsaw, say one out of ten, but it is easy to restring the bale. Just tie another piece of string about 16 inches long to the cut string and make a loop knot on one end. Put the other end through the loop, crank it down (pull it tight) and tie it off. Once square, the bales push together better and will help make the walls more stout with less voids. This means little or no stuffing with loose straw. When the bales are stacked, grab a 4-ft level, a couple of sledge hammers (or other ³bale bangers² as you prefer) and get another person to help. One of you should stand on the inside of the wall and the other one on the outside of the wall. Smack the bales so they don¹t overlap one another too much. Focus on getting one side as plumb as you can (for example, work on getting the inside plumb). Now trim the surface of the bales on both sides of the wall (inside and out) with a chainsaw or weed whacker. Be sure to do the whole wall, top to bottom. That will help to finish cleaning up any overlapping bales and any humps, bumps and lumps. This nice, plumb wall will make your lathing, netting, plastering and troweling process easier, not to mention the money you will save in stucco materials! And these beautiful, straight walls may make your building easier to sell in the future!