Craig Smith's method of sealing porous rubber cloth calls for the
use of acetone.  One should always have good ventilation when using
this very handy solvent because it is considered somewhat hazardous.
In the book, "Panic in the Pantry", the author strongly cautions
against using it.  The book covers the many materials commonly used
in industry, paints, etc.  When I worked in Tektronix's metallurgical
laboratory, we received a directive to cease using it even though we
had special ventilation booths.

Bill Chapman