Lead or iron cast keels come out of the mold looking pretty ugly. They are all faired before installation. If polyester based fairing compound is used, it will shrink and crack, sometime pieces will fall off.
The basic process is to clean to shiny metal, coat with neat epoxy and then fair using an epoxy based fairing compound. Epoxy has better adhesion properties than polyester and is less prone to shrinking.
A magnet will tell you if it cast iron or lead.