Repair or Replace a Damaged Chimney Crown
The chimney crown (also referred to as the chimney wash) is the top element of a masonry chimney. It covers and seals the top of the chimney from the flue liner to the chimney edge. The crown should provide a downward slope that will direct the water from the flue to the edge of the crown. The overhanging drip edge, by directing the run-off from the crown away from the chimney, helps prevent erosion of the brick and mortar in the chimney’s vertical surfaces. 
Most masonry chimneys are built with an inadequate crown constructed from common mortar mix that will crack, chip, or deteriorate from weather exposure. A proper chimney crown should be constructed of a Portland cement-based mixture and cast or formed so it provides an overhang projecting beyond all sides of the chimney by a minimum of two inches. The flue liner tile should also project above the crown a minimum of two inches.