Progress,  page 104
Next I wrapped the damper mechanism in more heavy rock wool.  I needed to build a strong
concrete beam across the damper to hold up the rest of the fireplace and all the rock facing yet
to come, and I felt it was important to again allow for thermal expansion differences.
I know this looks weird, but the opening I had allowed through the roof for the chimney was
offset from the eventual fireplace location by a couple of feet (poor foresight on my part) and I
needed an angled structure to start the chimney section.  Those seven triangular pieces are 4
inch thick concrete pavers 24 inches on a side that I cut on a diagonal.      Heavy suckers ...
Here's the form for the reinforced concrete mantel beam that spans the damper assembly.