A Leak in a Chimney Crown

Crown Location

• The crown on a chimney sits at the top of the chimney, around the chimney’s opening. The crown is made of mortar and slopes up from the top bricks on the chimney before it ends at the chimney’s opening. You may not be able to see the crown very well from the ground, but if you climb onto the roof, you should be able to see the crown clearly. Because of its location, you may not notice damage on the crown very easily.

Crack Formation

• Cracks can form in a chimney’s crown after periods of high moisture, which introduces moisture into the crown’s masonry. As the temperatures outside drop below the freezing point, the moisture in the masonry expands suddenly. This sudden expansion causes the chimney crown to crack because it does not have seams that allow for expansion and contraction. As more moisture finds its way into a crack and freezes, the cracks grow over time.

Leak Damage

• Water that leaks through the cracks in the chimney’s crown flows through the chimney’s flue and into the chimney’s shaft. The water can promote mold growth inside the chimney because it raises the humidity level inside the chimney. The mold growth collects on the mortar between the bricks, weakening the mortar to the point that it breaks apart. Without mortar to hold them in place, the bricks in the chimney begin falling out of place, possibly damaging the roof, any objects sitting at the side of the house or injuring anyone near the house when the bricks fall.

Crown Repair

• Once the crown on your chimney cracks, you do not necessarily need to remove it and install a new crown. Instead, you may patch the crown with fresh mortar, sealing the cracks. This solution, though, just means the crown will crack again later as it did before. If you want a longer-term solution that protects against cracks in the crown, you may hire a chimney sweep service to apply a seal to the cap that resists high heat and seals the crown’s mortar against moisture.