How strong are the rammed earth walls?
Traditionally, rammed earth walls used clay as the only glue holding the compacted soil together. But today, rammed earth construction uses some cement along with the dirt. The ratio of cement to earth depends on several factors, including the clay content of the dirt and the complexity of the building. We find that 10% cement makes for a strong earth wall. Like cement, rammed earth walls get stronger as they age. We have done compression tests on our rammed earth and achieved as high as 2880 psi but average 1,000 to 1,500 psi. This compares to cob (clay and straw) at 300 psi and adobe (clay brick) at 500 psi. Solid concrete has a psi of 2,500.
