I found this piece of cardboard in a box.  It was used for
some kind of packing.
Right!  I had the same idea!
Plaster was next to impossible to install in this location
and I wanted the wall curved like the terrain.
Real Road Concrete was my answer.
I traced the cardboard's outline onto a sheet of
concrete I had previously cast.  Then I cut out the
shape of the retaining wall.
I also cut out a solid piece of concrete to go
behind the arched piece, and there's a small piece
for the side of the wall. I just glued them all
together with testor's model cement.  It works
great for quickly bonding Real Road together.
continued...