The base cob wall for the west circular room will support the dome structure. Since the supporting wall is 2-feet thick, compared to the dome structure that will be between 12-14" thick, I needed to consider rain run-off as part of the design. The cross-section drawing below shows a triangular-shaped concrete pad (aka concrete pour-off) at the base of the dome that will allow water flow down the dome and off the wall. This will insure the long-term durability of the wall with minimum future maintenance.
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The photo below shows how the 'pour-off" was formed using the same Masonite strips anchored with 4"-deck screws and 1"x 2" wood strips (other examples can be found in this blog). The Masonite form extends 2" up from the top of the outer cob wall. The other side is 5" in height formed by using cob. 1/2"-diameter rebar in the trench, anchored by vertical rebar in the base wall can be seen in the photo (and the illustration above).
The next photo shows the trench poured with concrete. I added a brown concrete coloring to tone-down the typical concrete color look.
This next photo shows the completed work which covers about half the circumference of the circular base wall. The reason why the the pour-off doesn't go all the way around has to do with how the roofs for the remaining two rooms are to be built and will be covered later. Note: The black tar paper shown on the left, held down by tile fragments is temporary to protect the top of the wall from the summer monsoon rains.
The final picture is an overview of the west side of the building looking east.