The chimney crown is the concrete slab that blocks any direct water infiltration in the mortar joins. When the crown has several cracks, the last feet of your chimney will get weakened very quickly. In this specific case, the crown wasn’t built with reinforced concrete and wasn’t longer than the chimney’s lenght. These are the reasons why, despite the impressive thickness of the original crown, it got cracked and had generated significant damage between the joints of the stones. Strict standards regulate the type of crown to ask , it is important to follow them to prevent costly repairs. The thickness and the reinforcement of the crown, the flow of water as well as the expansion of the flue must all be taken into consideration when designing your crown!