May 03, 2020

Some Exterior Finishing Work

In my last post I covered the concrete bond beam that will support the beams and roof structure for the large room.  

In this post I want to show how I finished a section of wall along the south side of the studio that is common with the large room and a smaller room that extends out to the south. 

In the photograph below, the foreground is the roof of the smaller south room.  The 'cob' wall that is common with both rooms is capped by the bond beam that will support the aforementioned large room roof.

What I needed to figure-out was how to seal the exterior cob wall so rain would not deteriorate the wall and allow rain to infiltrate and undermine the rolled-roofing that extended up the wall creating a parapet (a 'flashing-type' solution).

The obvious solution for an exterior adobe wall would be traditional lime plaster.  However, for this small section and knowing from experience that south-facing abode walls with lime plaster need periodic maintenance due to thermal-expansion.  The daily hot-cold cycle of the desert here in Arivaca ranges  between 40-45 degrees F.; thus this expansion and contraction eventually results in the lime plaster separating from the adobe wall.  

There are mitigation solutions such as roof overhangs and ''chicken-wiring" the wall prior to plastering, but that's not how I wanted to approach this small section.


When pouring the bond beam I provided for a 2"overhang over the exterior of the cob wall.

In the photo below I used 1/4" cement board secured to the cob wall with 4" deck screws and large washers.  The cement board acted as 'flashing' as it is under the lip of the bond beam and then extends down over the top of the rolled-roofing so that it will shed water onto the roof below.  The cement board also acts as a substrate from which the applied cement mortar provides for a more robust finish.

I applied this same finish method to another part of the structure - again, in another small section where i was looking for a more 'maintenance-free' solution.  This time however, I added tiles made by a local potter to add an artistic touch (photo below).


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