With the summer (monsoon) season here in Southern Arizona, my cob structure is subject to short burst of heavy rains. The walls have been holding up surprisingly well over the years of construction but ultimately will need some type of water-resistant coating.
The traditional method has been a lime-plaster mix, but I went with a concrete-based stucco mix just for the The North and South parapet wall sections above the smaller sub-roofs. The rains came early and resulted in the shedding of straw and clay, creating a situation where drains could get clogged. I decided on a robust long-term stucco solution.
Wire mesh was applied and secured with 4-inch deck screws into the cob along with large washers to hold the mesh in place (See photo below showing the North parapet wall).
The photo below shows the South parapet wall with the wire mesh and a traditional stucco mix being applied. This stucco mix is concrete based which is traditionally frowned-upon because adobe wall should be able to breathe. However, I wanted a maintenance-free solution for these sections above the sub-roofs, so I went with the traditional stucco mix.
The photo below is the finished North wall still drying following the application of the stucco. The color was achieved by mixing-in 'concrete-color' available at Home Depot. I added two colors 'adobe' and 'clay'. I didn't measure or pre-test the mix of the two colors. I just took a shot and like the resulting shade.
I still need to add a 'top-cap' to the entire parapet wall, but the strong monsoon season has made work unpredictable and the heat/humidity, exhausting. I'll wait until early fall to apply the top cap.
In the meantime there are other projects to work on here at the cob studio.