ICC Requirements are Compression (Minimum #300 PSI)
& Modulus of Rupture (#50 Minimum PSI)
Adobe Certification from our testing lab guarantees documentation for Building Code officials. We have used Southern Arizona Testing Laboratories for ten years. We test our compression with a wet compression using an ASTM complete submersion test. We think it's a tougher test on the adobe because the sample has to remain submerged for 24 hrs until the crush.
To Compare and contrast the two methods of stabilization, let's look at the test required by building and safety officials in Arizona. Cement likes water and tends to absorb it and gain strength. Asphalt sheds water, preventing absorption, which causes the block to deteriorate. For this reason, two different tests are needed to adequately test the very different effects of the two stabilizers on the un-burnt, sun dried clay bricks. Bricks need to be waterproof if you want to leave them exposed. Even when plastering, it’s comforting to know that if water gets under the plaster, your walls will remain stable.
When testing a cement stabilized adobe, it is fully dried in an oven, the a 3.5” cube is soaked under water for 24 hours and immediately crushed to determine the stabilization and compression test results. Asphalt stabilized adobe is tested for stabilization by setting an oven dried 3.5” cube on a wet sponge for seven days. The cube is then weighed and must gain less than 2.5% of its dry weight to be a legally stabilized adobe. Compression testing on asphalt stabilized brick is done on a dry block.
A modulus of rupture test is also required. Both types of adobes are tested the same way. The lab snaps the block in the middle to test tensile strength. UBC codes require 300 PSI compression and 50# modulus of rupture for unfired adobe. San Tan Adobe guarantee’s IBC minimum requirements and is usually #500+ compression and #75+ modulus of rupture. An investment in stabilized adobe architecture should be maintenance free, and not require and expensive sealant job every year. Cement stabilized adobe requires no sealant, looks great, and will not erode, even in a parapet exposed wall.
The San Tan Adobe Company