Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>
Brittleness may be a factor if you move, remove the
toroid a lot. If it's always on top of your coil, it
may be less of an issue. Another thing to consider is
that aluminum expands and contracts due to temp. My
garage may see as high as 90 and as low as 32. If
plaster of paris (or other brittle fillers) expands
and contracts less than aluminum, it may loosen up
over time. If you just want smoothness, and are less
concerned with durability, why not just use roll upon
roll of masking or duct tape?