Century Boats and Fuel Tank issues

[Darrell Fico]

I have a 2000 Century CC 2600 that has developed a leak in the fuel tank. I'm attempting to seperate the hull from the deck in order to repair or replace the tank. The problem I've run into is that the seal between the two parts is mostly silicone caulking. Except for the transom. At this point, it seems a material is used that is very hard. Like cement with a granulated filler. Does anyone know what this material is and how to loosen it? I only want to cut the gelcoat as a last resort.