LOWELL BAKER on fri 25 oct 96
to answer your question honestly I havn't used either method of
insulating the arch; however...
If you choose to use fiber you should be cautious of a few things.
Primarily, don't compress the fiber any more than you must. It seems
the function of the castable is to hold the fiber in place and keep
it dry. It would also serve to keep the fiber particles from flying
around in the air you breathe.
I would recommend an aluminum foil layer between the fiber and
castable. This will serve to reflect the heat and keep the fiber dry
and also prevent the castable from soaking the fiber while you are
applying that layer.
Now to the If it were me side: Understanding that I am cheap by
nature, I would simply cover the brick with foil and then stack on
about three to five inches of the second (cheaper) castable. By the
time the heat gets through the first layer of brick it is not hot
enough the bother even that formula. You might put it down in
several layers which will serve to prevent cracking in direct lines
to the brick. You might even put down a few layers and then fire the
kiln then after a few firings add another layer.
As I write this I believe that even fiber glass insulation would
serve your purposes. The ceramic fiber is designed for hot face uses
and seems like over kill (let's don't start that line again). You
are not going to effect the fiber glass at the 1400-1500 degrees that
you might get at the outside of the single layer of arch brick.
It remains your call. I believe that any of the above or either of
your answers will work.
W. Lowell Baker
The University of Alabama
which can only be held partially responsible for my comments.
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