I personally haven't used the Ceramit... but I have read so many
dang books on nearly every jewelry technique and I remember
reading that the humidity can have an impact on how resins like
Ceramit set up.
I haven’t tried Ceramit, but if humidity is an issue buy a good
dehumidifier. I live in SC, and run an industrial unit constantly in
my studio to try and keep the humidity in a reasonable range. I got
mine at Grainger, an industrial supply chain. This might help, and
will certainly help your metal tools!
Beth in SC where it is actually NOT terribly humid today for a
change! It has been like soup around here all week.