caulker

/ˈkɔkər/
noun
  1. A person who fills seams or cracks in a ship or building with waterproof material.
    • The old caulker showed the apprentice how to seal the deck seams properly.
    • The caulker carefully pressed oakum into the gaps between the wooden planks.
    • My grandfather worked as a caulker in the shipyard for forty years.