My chimney crown has a couple of 1/4" cracks from the tile to the outside edge. Should I fill these before applying ChimneyRx Brushable Crown Repair? What type product should I use?

A high grade silicone caulk is typically used to seal minor cracks and voids prior to using the ChimneyRx Brushable Crown Repair. The ChimneyRx Crack & Joint Sealant would be used to seal mortar joints on any vertical surfaces which are outside the scope of the chimney crown.