If the chimney cap is absent or badly deteriorated, a new concrete cast crown maybe in order. The process begins by removing the old cement cap. Forms are used to cast the new concrete in place. This allows for a 3' overhang with a built in drip edge, to encourage moisture to fall from the structure verse running down the side. New concrete cast crowns are 4' thick with a sloping top for drainage. Concrete Cast Crowns have a 40 year warranty from the date of installation.