That is one of the problems with slate calls, the slate is like a spung and will change from day to day. One thing you can do is keep your slate calls in a ziplock bag it'll help keep them dry and when your not playing it turn it over slate down and set it on the bag. You can also heat the slate up with a lighter and dry it out a little, just be carefull that you don't over heat it and pop the glue loose. Also make sure your striker stays clean if it won't grab the slate it won't play for beans.
Dodge County NWTF Chapter
WI. Youth Turkey Mentor