There is only one answer for climate changes ----BONDO------
In 10 years i have never had to fix a popped slate seam with bondo.
Even though i like water putty in climate changes i have gone back to many times to fix popped seam or the putty raised up.
Slate absorbs water and swellswhen wet when it dries out it shrinks, so if your constantly changing conditions best of luck bondo never fails.
Do alittle research and look up realkingcobra posts you will learn alot from hes answer and quiz's