I just came across this guide:
https://barbonenet.wordpress.com/2017/02/08/how-to-make-the-compound-crackfree/
I know that his intentions are good and he wants to help our community but you should never ever "cook" your TIM unless you know exactly what is inside.
Depending on the TIM you have different types of polymers as matrix materials and the gases can be toxic if vaporized.
edit: Also: there is no water inside polymer TIMs.