External pinning is a simple, inexpensive way to make stronger buildings. This method is widely used to reinforce strawbale and earthbag buildings. External pinning is not always necessary. Structures such as domes or small roundhouses made with soil-filled earthbags usually do not need external pins. This process is mostly used to stabilize long straight walls and insulated earthbags. External pinning is particularly effective at reinforcing lightweight earthbags filled with scoria, pumice and other types of insulation.
Here’s the basic process. Lay lengths of baling twine, nylon cord or poly cord between courses of earthbags or straw bales as you build the wall. Leave about 10” or so of twine hanging on each side. Place the twine where you want the pins. Spacing of pins will vary depending on the design – 18”-24” apart is common. You can use rebar, saplings or bamboo pins. ‘Opposing pins’ means the pins are placed on opposite sides of the wall and tied tightly together. Work with a partner to install the pins. Tie one side, pull the twine tight and tie the other side. Done correctly with lots of force, the pins will be partially embedded in the wall.